Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Hi,

I finally found the time to rework the patches, but there are a few
things I want to discuss:

> > This breaks tools like clear_console that rely on flushing the
> > scrollback history by switching back and forth between consoles
> > which is why this feature is disabled by default.
> > Use the escape sequence \e[3J instead for flushing the buffer.
> 
> Have never heard of such tool as clear_console. Why mention it at all,
> where is it used, which are practical configurations which are broken in
> this way?
clear_console(1) is part of Debian's bash package and (I think) a
inofficial 'downstream' patch developed by Ubuntu [1]. There has been
security concerns (which is also why I disabled this feature by
default).
However, if there might be security issues, I would strongly suggest to
keep this part in the documentation - it does no harm anyway, does it?

> Does this break clear(1)?
No, my tests with clear(1) worked fine.

> > - Enter the amount of System RAM to allocate for the scrollback
> > -buffer.  Each 64KB will give you approximately 16 80x25
> > -screenfuls of scrollback buffer
> > + Enter the amount of System RAM to allocate for scrollback
> > + buffers of VGA consoles. Each 64KB will give you approximately
> > + 16 80x25 screenfuls of scrollback buffer.
> 
> Indentation amended, I don't know which way it should be, please
> double-check or mimic old indentation to stay on safe side.
Double-checked! That's at least how I read the docs.

> > +static struct vgacon_scrollback_info *vgacon_scrollback_cur;
> 
> Could you use name vgacon_scrollback instead of new
> vgacon_scrollback_cur? It doesn't change anything conceptually, but is a
> bit shorter and seems to mean current scrollback context anyway, right?
> 
> I think I see nothing to comment on below.
There is a already an array called 'vgacon_scrollbacks[N]', so I would
not like to have two variables named 'vgacon_scrollback' and
'vgacon_scrollbacks'. Either {'vgacon_scrollback_cur' and
'vgacon_scrollbacks'} or {'vgacon_scrollback' and
'vgacon_scrollback_list'}.
You can make a suggestion, if you like.

All other point you mentioned where fixed as you suggested.

Thanks again for your help, Andrey!

Best,

Manuel

[1]
http://manpages.ubuntu.com/manpages/xenial/en/man1/clear_console.1.html

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Hi,

I finally found the time to rework the patches, but there are a few
things I want to discuss:

> > This breaks tools like clear_console that rely on flushing the
> > scrollback history by switching back and forth between consoles
> > which is why this feature is disabled by default.
> > Use the escape sequence \e[3J instead for flushing the buffer.
> 
> Have never heard of such tool as clear_console. Why mention it at all,
> where is it used, which are practical configurations which are broken in
> this way?
clear_console(1) is part of Debian's bash package and (I think) a
inofficial 'downstream' patch developed by Ubuntu [1]. There has been
security concerns (which is also why I disabled this feature by
default).
However, if there might be security issues, I would strongly suggest to
keep this part in the documentation - it does no harm anyway, does it?

> Does this break clear(1)?
No, my tests with clear(1) worked fine.

> > - Enter the amount of System RAM to allocate for the scrollback
> > -buffer.  Each 64KB will give you approximately 16 80x25
> > -screenfuls of scrollback buffer
> > + Enter the amount of System RAM to allocate for scrollback
> > + buffers of VGA consoles. Each 64KB will give you approximately
> > + 16 80x25 screenfuls of scrollback buffer.
> 
> Indentation amended, I don't know which way it should be, please
> double-check or mimic old indentation to stay on safe side.
Double-checked! That's at least how I read the docs.

> > +static struct vgacon_scrollback_info *vgacon_scrollback_cur;
> 
> Could you use name vgacon_scrollback instead of new
> vgacon_scrollback_cur? It doesn't change anything conceptually, but is a
> bit shorter and seems to mean current scrollback context anyway, right?
> 
> I think I see nothing to comment on below.
There is a already an array called 'vgacon_scrollbacks[N]', so I would
not like to have two variables named 'vgacon_scrollback' and
'vgacon_scrollbacks'. Either {'vgacon_scrollback_cur' and
'vgacon_scrollbacks'} or {'vgacon_scrollback' and
'vgacon_scrollback_list'}.
You can make a suggestion, if you like.

All other point you mentioned where fixed as you suggested.

Thanks again for your help, Andrey!

Best,

Manuel

[1]
http://manpages.ubuntu.com/manpages/xenial/en/man1/clear_console.1.html

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Andrey Utkin]

On Mon, Sep 19, 2016 at 12:06:57AM +0200, Manuel Schölling wrote:
> Add a scrollback buffers for each VGA console. The benefit is that
> the scrollback history is not flushed when switching between consoles
> but is persistent.
> The buffers are allocated on demand when a new console is opened.

Hi,

I have noticed your message on #kernelnewbies IRC channel.

Thanks for the patch. This is definitely very useful, especially when
you boot into rescue system and use raw console and not a fancy
X11-based terminal app.

> 
> It always annoys me when I switch back to a console and I can just
> read half of an error backtrace. This should fix issues like these.

Personal feelings don't belong to commit messages. Previous paragraph is
enough to express the purpose.

> 
> This breaks tools like clear_console that rely on flushing the
> scrollback history by switching back and forth between consoles
> which is why this feature is disabled by default.
> Use the escape sequence \e[3J instead for flushing the buffer.

Have never heard of such tool as clear_console. Why mention it at all,
where is it used, which are practical configurations which are broken in
this way?

Does this break clear(1)?

> 
> Signed-off-by: Manuel Schölling 
> ---
> Changes in v3:
>   - Add config option for this feature
>   - Fallback to old scrollback buffer if kcalloc() fails
>   - Remove ioctl() call again and add documentation about existing
> escape sequence to flush the scrollback buffer
> Changes in v2:
>   - Add ioctl() call to flush scrollback buffer
>   - (Patch v2 was not labeled as such, sorry)
> ---
>  drivers/video/console/Kconfig  |  23 +-
>  drivers/video/console/vgacon.c | 160 
> +++--
>  2 files changed, 128 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index 38da6e2..67e52f0 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
> range 1 1024
> default "64"
> help
> - Enter the amount of System RAM to allocate for the scrollback
> -  buffer.  Each 64KB will give you approximately 16 80x25
> -  screenfuls of scrollback buffer
> +   Enter the amount of System RAM to allocate for scrollback
> +   buffers of VGA consoles. Each 64KB will give you approximately
> +   16 80x25 screenfuls of scrollback buffer.

Indentation amended, I don't know which way it should be, please
double-check or mimic old indentation to stay on safe side.

> +
> +config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE

Feels like bad naming. What about VGACON_SOFT_SCROLLBACK_PERSISTENT?

> + bool "Persistent Scrollback History for each console"
> + depends on VGACON_SOFT_SCROLLBACK
> + default n
> + help
> +   Say Y here if for each VGA console a scrollback buffer should
> +   be allocated. The scrollback history will persist when switching

Unnatural order of sentence IMHO, however I'm not native English.

> +   between consoles. If you say N here, scrollback is only supported
> +   for the active VGA console and scrollback history will be flushed
> +   when switching between consoles.

I think you may put less text here. You can skip details like "buffer
... allocated", just explain the difference in behaviour.

> +
> +   This breaks legacy versions of tools like clear_console which
> +   might cause security issues.
> +   Use the escape sequence \e[3J instead if this feature is activated.

See above. I'd drop this paragraph if clear(1) is not broken.

> +
> +   If you use a RAM-constrained system, say N here.

Which exactly cases to consider? I can't think of any practical one. You
may want to help user to figure out if he should consider this by
explaining that VGACON_SOFT_SCROLLBACK_SIZE is taken for each created
tty device (right?). Or drop this line :)

>  
>  config MDA_CONSOLE
>   depends on !M68K && !PARISC && ISA
> diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> index 1157661..e70e8fe 100644
> --- a/drivers/video/console/vgacon.c
> +++ b/drivers/video/console/vgacon.c
> @@ -1,5 +1,5 @@
>  /*
> - *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
> + *  linux/drivers/video/console/vgacon.c -- Low level VGA based console 
> driver

Cosmetic changes in separate patch please.

>   *
>   *   Created 28 Sep 1997 by Geert Uytterhoeven
>   *
> @@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
>  
>  #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
>  /* software scrollback */
> -static void *vgacon_scrollback;
> -static int vgacon_scrollback_tail;
> -static int vgacon_scrollback_size;
> -static int vgacon_scrollback_rows;
> -static int vgacon_scrollback_cnt;
> -static int vgacon_scrollback_cur;
> -static int vgacon_scrollback_save;
> -static int 

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Andrey Utkin]

On Mon, Sep 19, 2016 at 12:06:57AM +0200, Manuel Schölling wrote:
> Add a scrollback buffers for each VGA console. The benefit is that
> the scrollback history is not flushed when switching between consoles
> but is persistent.
> The buffers are allocated on demand when a new console is opened.

Hi,

I have noticed your message on #kernelnewbies IRC channel.

Thanks for the patch. This is definitely very useful, especially when
you boot into rescue system and use raw console and not a fancy
X11-based terminal app.

> 
> It always annoys me when I switch back to a console and I can just
> read half of an error backtrace. This should fix issues like these.

Personal feelings don't belong to commit messages. Previous paragraph is
enough to express the purpose.

> 
> This breaks tools like clear_console that rely on flushing the
> scrollback history by switching back and forth between consoles
> which is why this feature is disabled by default.
> Use the escape sequence \e[3J instead for flushing the buffer.

Have never heard of such tool as clear_console. Why mention it at all,
where is it used, which are practical configurations which are broken in
this way?

Does this break clear(1)?

> 
> Signed-off-by: Manuel Schölling 
> ---
> Changes in v3:
>   - Add config option for this feature
>   - Fallback to old scrollback buffer if kcalloc() fails
>   - Remove ioctl() call again and add documentation about existing
> escape sequence to flush the scrollback buffer
> Changes in v2:
>   - Add ioctl() call to flush scrollback buffer
>   - (Patch v2 was not labeled as such, sorry)
> ---
>  drivers/video/console/Kconfig  |  23 +-
>  drivers/video/console/vgacon.c | 160 
> +++--
>  2 files changed, 128 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index 38da6e2..67e52f0 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
> range 1 1024
> default "64"
> help
> - Enter the amount of System RAM to allocate for the scrollback
> -  buffer.  Each 64KB will give you approximately 16 80x25
> -  screenfuls of scrollback buffer
> +   Enter the amount of System RAM to allocate for scrollback
> +   buffers of VGA consoles. Each 64KB will give you approximately
> +   16 80x25 screenfuls of scrollback buffer.

Indentation amended, I don't know which way it should be, please
double-check or mimic old indentation to stay on safe side.

> +
> +config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE

Feels like bad naming. What about VGACON_SOFT_SCROLLBACK_PERSISTENT?

> + bool "Persistent Scrollback History for each console"
> + depends on VGACON_SOFT_SCROLLBACK
> + default n
> + help
> +   Say Y here if for each VGA console a scrollback buffer should
> +   be allocated. The scrollback history will persist when switching

Unnatural order of sentence IMHO, however I'm not native English.

> +   between consoles. If you say N here, scrollback is only supported
> +   for the active VGA console and scrollback history will be flushed
> +   when switching between consoles.

I think you may put less text here. You can skip details like "buffer
... allocated", just explain the difference in behaviour.

> +
> +   This breaks legacy versions of tools like clear_console which
> +   might cause security issues.
> +   Use the escape sequence \e[3J instead if this feature is activated.

See above. I'd drop this paragraph if clear(1) is not broken.

> +
> +   If you use a RAM-constrained system, say N here.

Which exactly cases to consider? I can't think of any practical one. You
may want to help user to figure out if he should consider this by
explaining that VGACON_SOFT_SCROLLBACK_SIZE is taken for each created
tty device (right?). Or drop this line :)

>  
>  config MDA_CONSOLE
>   depends on !M68K && !PARISC && ISA
> diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> index 1157661..e70e8fe 100644
> --- a/drivers/video/console/vgacon.c
> +++ b/drivers/video/console/vgacon.c
> @@ -1,5 +1,5 @@
>  /*
> - *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
> + *  linux/drivers/video/console/vgacon.c -- Low level VGA based console 
> driver

Cosmetic changes in separate patch please.

>   *
>   *   Created 28 Sep 1997 by Geert Uytterhoeven
>   *
> @@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
>  
>  #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
>  /* software scrollback */
> -static void *vgacon_scrollback;
> -static int vgacon_scrollback_tail;
> -static int vgacon_scrollback_size;
> -static int vgacon_scrollback_rows;
> -static int vgacon_scrollback_cnt;
> -static int vgacon_scrollback_cur;
> -static int vgacon_scrollback_save;
> -static int vgacon_scrollback_restore;
> -
> -static void 

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Greg KH]

On Mon, Sep 19, 2016 at 12:06:57AM +0200, Manuel Schölling wrote:
> Add a scrollback buffers for each VGA console. The benefit is that
> the scrollback history is not flushed when switching between consoles
> but is persistent.
> The buffers are allocated on demand when a new console is opened.
> 
> It always annoys me when I switch back to a console and I can just
> read half of an error backtrace. This should fix issues like these.
> 
> This breaks tools like clear_console that rely on flushing the
> scrollback history by switching back and forth between consoles
> which is why this feature is disabled by default.
> Use the escape sequence \e[3J instead for flushing the buffer.
> 
> Signed-off-by: Manuel Schölling 
> ---
> Changes in v3:
>   - Add config option for this feature
>   - Fallback to old scrollback buffer if kcalloc() fails
>   - Remove ioctl() call again and add documentation about existing
> escape sequence to flush the scrollback buffer
> Changes in v2:
>   - Add ioctl() call to flush scrollback buffer
>   - (Patch v2 was not labeled as such, sorry)
> ---
>  drivers/video/console/Kconfig  |  23 +-
>  drivers/video/console/vgacon.c | 160 
> +++--
>  2 files changed, 128 insertions(+), 55 deletions(-)

I need someone else to at least test this, and give an acked-by for
it...

thanks,

greg k-h

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Greg KH]

On Mon, Sep 19, 2016 at 12:06:57AM +0200, Manuel Schölling wrote:
> Add a scrollback buffers for each VGA console. The benefit is that
> the scrollback history is not flushed when switching between consoles
> but is persistent.
> The buffers are allocated on demand when a new console is opened.
> 
> It always annoys me when I switch back to a console and I can just
> read half of an error backtrace. This should fix issues like these.
> 
> This breaks tools like clear_console that rely on flushing the
> scrollback history by switching back and forth between consoles
> which is why this feature is disabled by default.
> Use the escape sequence \e[3J instead for flushing the buffer.
> 
> Signed-off-by: Manuel Schölling 
> ---
> Changes in v3:
>   - Add config option for this feature
>   - Fallback to old scrollback buffer if kcalloc() fails
>   - Remove ioctl() call again and add documentation about existing
> escape sequence to flush the scrollback buffer
> Changes in v2:
>   - Add ioctl() call to flush scrollback buffer
>   - (Patch v2 was not labeled as such, sorry)
> ---
>  drivers/video/console/Kconfig  |  23 +-
>  drivers/video/console/vgacon.c | 160 
> +++--
>  2 files changed, 128 insertions(+), 55 deletions(-)

I need someone else to at least test this, and give an acked-by for
it...

thanks,

greg k-h

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Hi Tomi,

I thought I'd let you, Tomi, (and all the others) know what the patch
does:

There is currently a single scrollback buffer (vgacon_scrollback) that
contains the text of the current console. When you switch the console it
is cleared and re-used for the new console.
My patch simply replaced the single scrollback buffer with an array of
scrollback buffers. One for each console.

A quick shout out to everybody else: Tomi told me today that he is
currently short on time to review this patch, so any Reviewed-by or
Tested-by would be very appreciated.

Bye,

Manuel


On Mo, 2016-09-19 at 00:06 +0200, Manuel Schölling wrote:
> Add a scrollback buffers for each VGA console. The benefit is that
> the scrollback history is not flushed when switching between consoles
> but is persistent.
> The buffers are allocated on demand when a new console is opened.
> 
> It always annoys me when I switch back to a console and I can just
> read half of an error backtrace. This should fix issues like these.
> 
> This breaks tools like clear_console that rely on flushing the
> scrollback history by switching back and forth between consoles
> which is why this feature is disabled by default.
> Use the escape sequence \e[3J instead for flushing the buffer.
> 
> Signed-off-by: Manuel Schölling 
> ---
> Changes in v3:
>   - Add config option for this feature
>   - Fallback to old scrollback buffer if kcalloc() fails
>   - Remove ioctl() call again and add documentation about existing
> escape sequence to flush the scrollback buffer
> Changes in v2:
>   - Add ioctl() call to flush scrollback buffer
>   - (Patch v2 was not labeled as such, sorry)
> ---
>  drivers/video/console/Kconfig  |  23 +-
>  drivers/video/console/vgacon.c | 160 
> +++--
>  2 files changed, 128 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index 38da6e2..67e52f0 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
> range 1 1024
> default "64"
> help
> - Enter the amount of System RAM to allocate for the scrollback
> -  buffer.  Each 64KB will give you approximately 16 80x25
> -  screenfuls of scrollback buffer
> +   Enter the amount of System RAM to allocate for scrollback
> +   buffers of VGA consoles. Each 64KB will give you approximately
> +   16 80x25 screenfuls of scrollback buffer.
> +
> +config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
> + bool "Persistent Scrollback History for each console"
> + depends on VGACON_SOFT_SCROLLBACK
> + default n
> + help
> +   Say Y here if for each VGA console a scrollback buffer should
> +   be allocated. The scrollback history will persist when switching
> +   between consoles. If you say N here, scrollback is only supported
> +   for the active VGA console and scrollback history will be flushed
> +   when switching between consoles.
> +
> +   This breaks legacy versions of tools like clear_console which
> +   might cause security issues.
> +   Use the escape sequence \e[3J instead if this feature is activated.
> +
> +   If you use a RAM-constrained system, say N here.
>  
>  config MDA_CONSOLE
>   depends on !M68K && !PARISC && ISA
> diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> index 1157661..e70e8fe 100644
> --- a/drivers/video/console/vgacon.c
> +++ b/drivers/video/console/vgacon.c
> @@ -1,5 +1,5 @@
>  /*
> - *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
> + *  linux/drivers/video/console/vgacon.c -- Low level VGA based console 
> driver
>   *
>   *   Created 28 Sep 1997 by Geert Uytterhoeven
>   *
> @@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
>  
>  #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
>  /* software scrollback */
> -static void *vgacon_scrollback;
> -static int vgacon_scrollback_tail;
> -static int vgacon_scrollback_size;
> -static int vgacon_scrollback_rows;
> -static int vgacon_scrollback_cnt;
> -static int vgacon_scrollback_cur;
> -static int vgacon_scrollback_save;
> -static int vgacon_scrollback_restore;
> -
> -static void vgacon_scrollback_init(int pitch)
> +struct vgacon_scrollback_info {
> + void *data;
> + int tail;
> + int size;
> + int rows;
> + int cnt;
> + int cur;
> + int save;
> + int restore;
> +};
> +static struct vgacon_scrollback_info *vgacon_scrollback_cur;
> +#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
> +static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
> +#else
> +static struct vgacon_scrollback_info vgacon_scrollbacks[1];
> +#endif
> +
> +static void vgacon_scrollback_reset(size_t reset_size)
>  {
> - int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
> -
> - if (vgacon_scrollback) {
> -  

Re: [PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Hi Tomi,

I thought I'd let you, Tomi, (and all the others) know what the patch
does:

There is currently a single scrollback buffer (vgacon_scrollback) that
contains the text of the current console. When you switch the console it
is cleared and re-used for the new console.
My patch simply replaced the single scrollback buffer with an array of
scrollback buffers. One for each console.

A quick shout out to everybody else: Tomi told me today that he is
currently short on time to review this patch, so any Reviewed-by or
Tested-by would be very appreciated.

Bye,

Manuel


On Mo, 2016-09-19 at 00:06 +0200, Manuel Schölling wrote:
> Add a scrollback buffers for each VGA console. The benefit is that
> the scrollback history is not flushed when switching between consoles
> but is persistent.
> The buffers are allocated on demand when a new console is opened.
> 
> It always annoys me when I switch back to a console and I can just
> read half of an error backtrace. This should fix issues like these.
> 
> This breaks tools like clear_console that rely on flushing the
> scrollback history by switching back and forth between consoles
> which is why this feature is disabled by default.
> Use the escape sequence \e[3J instead for flushing the buffer.
> 
> Signed-off-by: Manuel Schölling 
> ---
> Changes in v3:
>   - Add config option for this feature
>   - Fallback to old scrollback buffer if kcalloc() fails
>   - Remove ioctl() call again and add documentation about existing
> escape sequence to flush the scrollback buffer
> Changes in v2:
>   - Add ioctl() call to flush scrollback buffer
>   - (Patch v2 was not labeled as such, sorry)
> ---
>  drivers/video/console/Kconfig  |  23 +-
>  drivers/video/console/vgacon.c | 160 
> +++--
>  2 files changed, 128 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index 38da6e2..67e52f0 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
> range 1 1024
> default "64"
> help
> - Enter the amount of System RAM to allocate for the scrollback
> -  buffer.  Each 64KB will give you approximately 16 80x25
> -  screenfuls of scrollback buffer
> +   Enter the amount of System RAM to allocate for scrollback
> +   buffers of VGA consoles. Each 64KB will give you approximately
> +   16 80x25 screenfuls of scrollback buffer.
> +
> +config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
> + bool "Persistent Scrollback History for each console"
> + depends on VGACON_SOFT_SCROLLBACK
> + default n
> + help
> +   Say Y here if for each VGA console a scrollback buffer should
> +   be allocated. The scrollback history will persist when switching
> +   between consoles. If you say N here, scrollback is only supported
> +   for the active VGA console and scrollback history will be flushed
> +   when switching between consoles.
> +
> +   This breaks legacy versions of tools like clear_console which
> +   might cause security issues.
> +   Use the escape sequence \e[3J instead if this feature is activated.
> +
> +   If you use a RAM-constrained system, say N here.
>  
>  config MDA_CONSOLE
>   depends on !M68K && !PARISC && ISA
> diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> index 1157661..e70e8fe 100644
> --- a/drivers/video/console/vgacon.c
> +++ b/drivers/video/console/vgacon.c
> @@ -1,5 +1,5 @@
>  /*
> - *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
> + *  linux/drivers/video/console/vgacon.c -- Low level VGA based console 
> driver
>   *
>   *   Created 28 Sep 1997 by Geert Uytterhoeven
>   *
> @@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
>  
>  #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
>  /* software scrollback */
> -static void *vgacon_scrollback;
> -static int vgacon_scrollback_tail;
> -static int vgacon_scrollback_size;
> -static int vgacon_scrollback_rows;
> -static int vgacon_scrollback_cnt;
> -static int vgacon_scrollback_cur;
> -static int vgacon_scrollback_save;
> -static int vgacon_scrollback_restore;
> -
> -static void vgacon_scrollback_init(int pitch)
> +struct vgacon_scrollback_info {
> + void *data;
> + int tail;
> + int size;
> + int rows;
> + int cnt;
> + int cur;
> + int save;
> + int restore;
> +};
> +static struct vgacon_scrollback_info *vgacon_scrollback_cur;
> +#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
> +static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
> +#else
> +static struct vgacon_scrollback_info vgacon_scrollbacks[1];
> +#endif
> +
> +static void vgacon_scrollback_reset(size_t reset_size)
>  {
> - int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
> -
> - if (vgacon_scrollback) {
> - 

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) 

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) {
+   

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) 

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) {
+   

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) 

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) {
+   

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) 

[PATCH v3] console: Add persistent scrollback buffers for all VGA consoles

[Manuel Schölling]

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

It always annoys me when I switch back to a console and I can just
read half of an error backtrace. This should fix issues like these.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling 
---
Changes in v3:
  - Add config option for this feature
  - Fallback to old scrollback buffer if kcalloc() fails
  - Remove ioctl() call again and add documentation about existing
escape sequence to flush the scrollback buffer
Changes in v2:
  - Add ioctl() call to flush scrollback buffer
  - (Patch v2 was not labeled as such, sorry)
---
 drivers/video/console/Kconfig  |  23 +-
 drivers/video/console/vgacon.c | 160 +++--
 2 files changed, 128 insertions(+), 55 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..67e52f0 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,26 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
-buffer.  Each 64KB will give you approximately 16 80x25
-screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+   bool "Persistent Scrollback History for each console"
+   depends on VGACON_SOFT_SCROLLBACK
+   default n
+   help
+ Say Y here if for each VGA console a scrollback buffer should
+ be allocated. The scrollback history will persist when switching
+ between consoles. If you say N here, scrollback is only supported
+ for the active VGA console and scrollback history will be flushed
+ when switching between consoles.
+
+ This breaks legacy versions of tools like clear_console which
+ might cause security issues.
+ Use the escape sequence \e[3J instead if this feature is activated.
+
+ If you use a RAM-constrained system, say N here.
 
 config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 1157661..e70e8fe 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1,5 +1,5 @@
 /*
- *  linux/drivers/video/vgacon.c -- Low level VGA based console driver
+ *  linux/drivers/video/console/vgacon.c -- Low level VGA based console driver
  *
  * Created 28 Sep 1997 by Geert Uytterhoeven
  *
@@ -181,70 +181,125 @@ static inline void vga_set_mem_top(struct vc_data *c)
 
 #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
 /* software scrollback */
-static void *vgacon_scrollback;
-static int vgacon_scrollback_tail;
-static int vgacon_scrollback_size;
-static int vgacon_scrollback_rows;
-static int vgacon_scrollback_cnt;
-static int vgacon_scrollback_cur;
-static int vgacon_scrollback_save;
-static int vgacon_scrollback_restore;
-
-static void vgacon_scrollback_init(int pitch)
+struct vgacon_scrollback_info {
+   void *data;
+   int tail;
+   int size;
+   int rows;
+   int cnt;
+   int cur;
+   int save;
+   int restore;
+};
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_FOR_EACH_CONSOLE
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif
+
+static void vgacon_scrollback_reset(size_t reset_size)
 {
-   int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
-   if (vgacon_scrollback) {
-   vgacon_scrollback_cnt  = 0;
-   vgacon_scrollback_tail = 0;
-   vgacon_scrollback_cur  = 0;
-   vgacon_scrollback_rows = rows - 1;
-   vgacon_scrollback_size = rows * pitch;
+   if (vgacon_scrollback_cur->data && reset_size > 0)
+   memset(vgacon_scrollback_cur->data, 0, reset_size);
+
+   vgacon_scrollback_cur->cnt  = 0;
+   vgacon_scrollback_cur->tail = 0;
+   vgacon_scrollback_cur->cur  = 0;
+}
+
+static void vgacon_scrollback_init(int vc_num)
+{
+   int pitch = vga_video_num_columns * 2;
+   size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+   int rows = size/pitch;
+   void *data;
+
+   data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024, GFP_NOWAIT);
+   if (data) {
+