Re: [PATCH 2/2] fbcon: Defer console takeover for splash screens to first switch
On 27/2/24 21:47, Hans de Goede wrote: > Hi, > > On 2/27/24 02:06, Daniel van Vugt wrote: >> On 27/2/24 02:23, Hans de Goede wrote: >>> Hi All, >>> >>> On 2/2/24 09:53, Daniel van Vugt wrote: >>>> Until now, deferred console takeover only meant defer until there is >>>> output. But that risks stepping on the toes of userspace splash screens, >>>> as console messages may appear before the splash screen. So check for the >>>> "splash" parameter (as used by Plymouth) and if present then extend the >>>> deferral until the first switch. >>> >>> Daniel, thank you for your patch but I do not believe that this >>> is the right solution. Deferring fbcon takeover further then >>> after the first text is output means that any errors about e.g. >>> a corrupt initrd or the kernel erroring out / crashing will not >>> be visible. >> >> That's not really correct. If a boot failure has occurred after the splash >> then >> pressing escape shows the log. > > Hmm, I guess this is with the latest plymouth which has a builtin terminal > emulator for kernels without VT support ? Pressing ESC does not to a VC > switch and AFAICT that is what you are triggering on to allow fbcon takeover > after this patches. > >> If a boot failure has occurred before the splash >> then it can be debugged visually by rebooting without the "splash" parameter. > > Which requires the user to know this and requires the user to know how to > edit kernel cmdline parameters in e.g. grub. This is not a good user > experience. We want inexperienced users to just be able to point > a phone camera at the screen and take a picture of the errors. As the person who contributes most to Ubuntu bug triage I have a pretty good idea of what users experience. And when they do experience boot failures it's either with a blank screen already (because userspace, not the kernel's fault), or they report an error message to us that's not relevant to the real failure. In both cases our users understand (or learn quickly) the ease with which they can reboot either to recovery mode, or a previous kernel. We then direct them to collect the full log of the failed boot. Because even if they were booting with a full text console, most of those bugs don't reveal themselves on the console. If they did then they'd be visible in the system journal along with everything else. What is not a "good user experience" is the boot messages people are shown on every boot. > > >>> When the kernel e.g. oopses or panics because of not finding >>> its rootfs (I tested the latter option when writing the original >>> deferred fbcon takeover code) then fbcon must takeover and >>> print the messages from the dying kernel so that the user has >>> some notion of what is going wrong. >> >> Indeed, just reboot without the "splash" parameter to do that. > > Again not something beginning Linux users will be able to do, > what happened to "Ubuntu: Linux for Human Beings" ? It is more user-friendly than it sounds. Just reboot, trigger the grub menu and select recovery mode or an older kernel (which is always available). I think some boot failures also take you to the grub menu automatically next time? > >>> And since your patch seems to delay switching till the first >>> vc-switch this means that e.g. even after say gdm refusing >>> to start because of issues there still will be no text >>> output. This makes debugging various issues much harder. >> >> I've debugged many gdm failures and it is never useful to use the console for >> those. Reboot and get the system journal instead. > > But users will not see any errors now, meaning they don't > even know where to begin with troubleshooting ... Indeed. I deal with those users every day and they log their bugs against the wrong components, understandably. We then work with them to triage and reassign the issue to the right place. > >>> Moreover Fedora has been doing flickerfree boot for many >>> years without needing this. >> >> I believe Fedora has a mostly working solution, but not totally reliable, as >> mentioned in the commit message: >> >> "even systems whose splash exists in initrd may not be not immune because >> they >> still rely on racing against all possible kernel messages that might >> trigger the fbcon takeover" > > Only very serious kernel errors like oopses or panics will > trigger the takeover and that is *exactly* what we want. > > There is a race where plymouth may hide such vary serious > messages, if
Re: [PATCH 2/2] fbcon: Defer console takeover for splash screens to first switch
On 27/2/24 02:23, Hans de Goede wrote: > Hi All, > > On 2/2/24 09:53, Daniel van Vugt wrote: >> Until now, deferred console takeover only meant defer until there is >> output. But that risks stepping on the toes of userspace splash screens, >> as console messages may appear before the splash screen. So check for the >> "splash" parameter (as used by Plymouth) and if present then extend the >> deferral until the first switch. > > Daniel, thank you for your patch but I do not believe that this > is the right solution. Deferring fbcon takeover further then > after the first text is output means that any errors about e.g. > a corrupt initrd or the kernel erroring out / crashing will not > be visible. That's not really correct. If a boot failure has occurred after the splash then pressing escape shows the log. If a boot failure has occurred before the splash then it can be debugged visually by rebooting without the "splash" parameter. > > When the kernel e.g. oopses or panics because of not finding > its rootfs (I tested the latter option when writing the original > deferred fbcon takeover code) then fbcon must takeover and > print the messages from the dying kernel so that the user has > some notion of what is going wrong. Indeed, just reboot without the "splash" parameter to do that. > > And since your patch seems to delay switching till the first > vc-switch this means that e.g. even after say gdm refusing > to start because of issues there still will be no text > output. This makes debugging various issues much harder. I've debugged many gdm failures and it is never useful to use the console for those. Reboot and get the system journal instead. > > Moreover Fedora has been doing flickerfree boot for many > years without needing this. I believe Fedora has a mostly working solution, but not totally reliable, as mentioned in the commit message: "even systems whose splash exists in initrd may not be not immune because they still rely on racing against all possible kernel messages that might trigger the fbcon takeover" > > The kernel itself will be quiet as long as you set > CONFIG_CONSOLE_LOGLEVEL_QUIET=3 Ubuntu atm has set this > to 4 which means any kernel pr_err() or dev_err() > messages will get through and since there are quite > a few false positives of those Ubuntu really needs > to set CONFIG_CONSOLE_LOGLEVEL_QUIET=3 to fix part of: > https://bugs.launchpad.net/bugs/1970069 Incorrect. In my testing some laptops needed log level as low as 2 to go quiet. And the Ubuntu kernel team is never going to fix all those for non-sponsored devices. > > After that it is "just" a matter of not making userspace > output anything unless it has errors to report. > > systemd already is quiet by default (only logging > errors) when quiet is on the kernel commandline. Unfortunately not true for Ubuntu. We carry a noisy systemd patch which I'm told we can't remove in the short term: https://bugs.launchpad.net/ubuntu/+source/plymouth/+bug/1970069/comments/39 > > So any remaining issues are Ubuntu specific boot > process bits and Ubuntu really should be able to > make those by silent unless they have important > info (errors or other unexpected things) to report. > > Given that this will make debugging boot issues > much harder and that there are other IMHO better > alternatives I'm nacking this patch: NACK. > > FWIW I believe that I'm actually saving Ubuntu > from shooting themselves in the foot here, > hiding all sort of boot errors (like the initrd > not finding /) until the user does a magic > alt+f2 followed by alt+f1 incantation really is > not doing yourself any favors wrt debugging any > sort of boot failures. > > Regards, > > Hans Thanks for your input, but I respectfully disagree and did consider these points already. - Daniel > > > > > >> Closes: https://bugs.launchpad.net/bugs/1970069 >> Cc: Mario Limonciello >> Signed-off-by: Daniel van Vugt >> --- >> drivers/video/fbdev/core/fbcon.c | 32 +--- >> 1 file changed, 29 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/video/fbdev/core/fbcon.c >> b/drivers/video/fbdev/core/fbcon.c >> index 63af6ab034..5b9f7635f7 100644 >> --- a/drivers/video/fbdev/core/fbcon.c >> +++ b/drivers/video/fbdev/core/fbcon.c >> @@ -76,6 +76,7 @@ >> #include /* For counting font checksums */ >> #include >> #include >> +#include >> >> #include "fbcon.h" >> #include "fb_internal.h" >> @@ -146,6 +147,7 @@ static inline void fbcon_map_override(void) >> >> #ifdef CONFIG_FRAMEB
[PATCH v4 2/2] fbcon: Defer console takeover for splash screens to first switch
Until now, deferred console takeover only meant defer until there is
output. But that risks stepping on the toes of userspace splash screens
as console messages may appear before the splash screen.
This becomes more likely the later the splash screen starts, but even
systems whose splash exists in initrd may not be not immune because they
still rely on racing against all possible kernel messages that might
trigger the fbcon takeover. And those kernel messages are hardware
dependent so what boots silently on one machine may not be so quiet on
the next. We also want to shield users from seeing warnings about their
hardware/firmware that they don't always have the power to fix themselves,
and may not be deemed worthy of fixing by the vendor.
So now we check the command line for the expectation of userspace splash
(CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION) and if present
then defer fbcon's takeover until the first console switch. In the case
of Plymouth, its value would typically be "splash". This keeps the boot
experience clean and silent so long as the command line requests so.
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello
Signed-off-by: Daniel van Vugt
---
v2: Added Kconfig option instead of hard coding "splash".
v3: Default to disabled, not "splash". If enabled then take over on
switch rather than on first output after switch.
v4: Elaborate more in the commit message about races and Kconfig. Also
move these revision comments below the line marker.
---
drivers/video/console/Kconfig| 12 +
drivers/video/fbdev/core/fbcon.c | 44 +---
2 files changed, 52 insertions(+), 4 deletions(-)
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index bc31db6ef7..2f9435335f 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -138,6 +138,18 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
by the firmware in place, rather then replacing the contents with a
black screen as soon as fbcon loads.
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ string "Command line parameter to defer takeover to first switch"
+ depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+ default ""
+ help
+ If enabled this defers further the framebuffer console taking over
+ until the first console switch has occurred. And even then only if
+ the specified parameter is found on the command line. This ensures
+ fbcon does not interrupt userspace splash screens such as Plymouth
+ which may be yet to start rendering at the time of the first console
+ output.
+
config STI_CONSOLE
bool "STI text console"
depends on PARISC && HAS_IOMEM
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 1183e7a871..e5d841ab03 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -76,6 +76,7 @@
#include /* For counting font checksums */
#include
#include
+#include
#include "fbcon.h"
#include "fb_internal.h"
@@ -3348,7 +3349,7 @@ static int fbcon_output_notifier(struct notifier_block
*nb,
{
WARN_CONSOLE_UNLOCKED();
- pr_info("fbcon: Taking over console\n");
+ pr_info("fbcon: Taking over console for output\n");
dummycon_unregister_output_notifier(_output_nb);
@@ -3357,6 +3358,27 @@ static int fbcon_output_notifier(struct notifier_block
*nb,
return NOTIFY_OK;
}
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+static int initial_console;
+static struct notifier_block fbcon_switch_nb;
+
+static int fbcon_switch_notifier(struct notifier_block *nb,
+unsigned long action, void *data)
+{
+ struct vc_data *vc = data;
+
+ WARN_CONSOLE_UNLOCKED();
+
+ if (vc->vc_num != initial_console) {
+ pr_info("fbcon: Taking over console for switch\n");
+ dummycon_unregister_switch_notifier(_switch_nb);
+ schedule_work(_deferred_takeover_work);
+ }
+
+ return NOTIFY_OK;
+}
+#endif
#endif
static void fbcon_start(void)
@@ -3368,8 +3390,18 @@ static void fbcon_start(void)
deferred_takeover = false;
if (deferred_takeover) {
- fbcon_output_nb.notifier_call = fbcon_output_notifier;
- dummycon_register_output_notifier(_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ if (cmdline_find_option_bool(boot_command_line,
+ CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
+ initial_console = fg_console;
+ fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
+ dummycon_register_switch_not
[PATCH v4 1/2] dummycon: Add dummycon_(un)register_switch_notifier
To detect switch attempts before a real console exists. This will be
used for the same purpose as dummycon_(un)register_output_notifier,
for fbcon to detect a more polite time to take over.
Signed-off-by: Daniel van Vugt
---
drivers/video/console/dummycon.c | 35 +++-
include/linux/console.h | 2 ++
2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 14af5d9e13..55e9b600ce 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -83,6 +83,32 @@ static int dummycon_blank(struct vc_data *vc, int blank, int
mode_switch)
/* Redraw, so that we get putc(s) for output done while blanked */
return 1;
}
+
+/* This is protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_switch_nh);
+
+void dummycon_register_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_register(_switch_nh, nb);
+}
+
+void dummycon_unregister_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_unregister(_switch_nh, nb);
+}
+
+static int dummycon_switch(struct vc_data *vc)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_call_chain(_switch_nh, 0, vc);
+
+ return 0;
+}
#else
static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
@@ -91,6 +117,10 @@ static int dummycon_blank(struct vc_data *vc, int blank,
int mode_switch)
{
return 0;
}
+static int dummycon_switch(struct vc_data *vc)
+{
+ return 0;
+}
#endif
static const char *dummycon_startup(void)
@@ -120,11 +150,6 @@ static bool dummycon_scroll(struct vc_data *vc, unsigned
int top,
return false;
}
-static int dummycon_switch(struct vc_data *vc)
-{
- return 0;
-}
-
/*
* The console `switch' structure for the dummy console
*
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8..8fd70ae623 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -531,5 +531,7 @@ extern void console_init(void);
/* For deferred console takeover */
void dummycon_register_output_notifier(struct notifier_block *nb);
void dummycon_unregister_output_notifier(struct notifier_block *nb);
+void dummycon_register_switch_notifier(struct notifier_block *nb);
+void dummycon_unregister_switch_notifier(struct notifier_block *nb);
#endif /* _LINUX_CONSOLE_H */
--
2.43.0
[PATCH v3 2/2] fbcon: Defer console takeover for splash screens to first switch
Until now, deferred console takeover only meant defer until there is
output. But that risks stepping on the toes of userspace splash screens,
as console messages may appear before the splash screen. So check the
command line for the expectation of userspace splash and if present then
extend the deferral until the first switch.
v2: Added Kconfig option instead of hard coding "splash".
v3: Default to disabled, not "splash". If enabled then take over on
switch rather than on first output after switch.
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello
Signed-off-by: Daniel van Vugt
---
drivers/video/console/Kconfig| 12 +
drivers/video/fbdev/core/fbcon.c | 44 +---
2 files changed, 52 insertions(+), 4 deletions(-)
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index bc31db6ef7..2f9435335f 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -138,6 +138,18 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
by the firmware in place, rather then replacing the contents with a
black screen as soon as fbcon loads.
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ string "Command line parameter to defer takeover to first switch"
+ depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+ default ""
+ help
+ If enabled this defers further the framebuffer console taking over
+ until the first console switch has occurred. And even then only if
+ the specified parameter is found on the command line. This ensures
+ fbcon does not interrupt userspace splash screens such as Plymouth
+ which may be yet to start rendering at the time of the first console
+ output.
+
config STI_CONSOLE
bool "STI text console"
depends on PARISC && HAS_IOMEM
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 1183e7a871..e5d841ab03 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -76,6 +76,7 @@
#include /* For counting font checksums */
#include
#include
+#include
#include "fbcon.h"
#include "fb_internal.h"
@@ -3348,7 +3349,7 @@ static int fbcon_output_notifier(struct notifier_block
*nb,
{
WARN_CONSOLE_UNLOCKED();
- pr_info("fbcon: Taking over console\n");
+ pr_info("fbcon: Taking over console for output\n");
dummycon_unregister_output_notifier(_output_nb);
@@ -3357,6 +3358,27 @@ static int fbcon_output_notifier(struct notifier_block
*nb,
return NOTIFY_OK;
}
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+static int initial_console;
+static struct notifier_block fbcon_switch_nb;
+
+static int fbcon_switch_notifier(struct notifier_block *nb,
+unsigned long action, void *data)
+{
+ struct vc_data *vc = data;
+
+ WARN_CONSOLE_UNLOCKED();
+
+ if (vc->vc_num != initial_console) {
+ pr_info("fbcon: Taking over console for switch\n");
+ dummycon_unregister_switch_notifier(_switch_nb);
+ schedule_work(_deferred_takeover_work);
+ }
+
+ return NOTIFY_OK;
+}
+#endif
#endif
static void fbcon_start(void)
@@ -3368,8 +3390,18 @@ static void fbcon_start(void)
deferred_takeover = false;
if (deferred_takeover) {
- fbcon_output_nb.notifier_call = fbcon_output_notifier;
- dummycon_register_output_notifier(_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ if (cmdline_find_option_bool(boot_command_line,
+ CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
+ initial_console = fg_console;
+ fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
+ dummycon_register_switch_notifier(_switch_nb);
+ } else
+#endif
+ {
+ fbcon_output_nb.notifier_call = fbcon_output_notifier;
+ dummycon_register_output_notifier(_output_nb);
+ }
return;
}
#endif
@@ -3416,8 +3448,12 @@ void __exit fb_console_exit(void)
{
#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
console_lock();
- if (deferred_takeover)
+ if (deferred_takeover) {
dummycon_unregister_output_notifier(_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ dummycon_unregister_switch_notifier(_switch_nb);
+#endif
+ }
console_unlock();
cancel_work_sync(_deferred_takeover_work);
--
2.43.0
[PATCH v3 1/2] dummycon: Add dummycon_(un)register_switch_notifier
To detect switch attempts before a real console exists. This will be
used for the same purpose as dummycon_(un)register_output_notifier,
for fbcon to detect a more polite time to take over.
Signed-off-by: Daniel van Vugt
---
drivers/video/console/dummycon.c | 35 +++-
include/linux/console.h | 2 ++
2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 14af5d9e13..55e9b600ce 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -83,6 +83,32 @@ static int dummycon_blank(struct vc_data *vc, int blank, int
mode_switch)
/* Redraw, so that we get putc(s) for output done while blanked */
return 1;
}
+
+/* This is protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_switch_nh);
+
+void dummycon_register_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_register(_switch_nh, nb);
+}
+
+void dummycon_unregister_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_unregister(_switch_nh, nb);
+}
+
+static int dummycon_switch(struct vc_data *vc)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_call_chain(_switch_nh, 0, vc);
+
+ return 0;
+}
#else
static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
@@ -91,6 +117,10 @@ static int dummycon_blank(struct vc_data *vc, int blank,
int mode_switch)
{
return 0;
}
+static int dummycon_switch(struct vc_data *vc)
+{
+ return 0;
+}
#endif
static const char *dummycon_startup(void)
@@ -120,11 +150,6 @@ static bool dummycon_scroll(struct vc_data *vc, unsigned
int top,
return false;
}
-static int dummycon_switch(struct vc_data *vc)
-{
- return 0;
-}
-
/*
* The console `switch' structure for the dummy console
*
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8..8fd70ae623 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -531,5 +531,7 @@ extern void console_init(void);
/* For deferred console takeover */
void dummycon_register_output_notifier(struct notifier_block *nb);
void dummycon_unregister_output_notifier(struct notifier_block *nb);
+void dummycon_register_switch_notifier(struct notifier_block *nb);
+void dummycon_unregister_switch_notifier(struct notifier_block *nb);
#endif /* _LINUX_CONSOLE_H */
--
2.43.0
Re: [PATCH v2 2/2] fbcon: Defer console takeover for splash screens to first switch
On 9/2/24 18:58, Daniel Vetter wrote: > On Thu, Feb 08, 2024 at 09:16:50AM +0800, Daniel van Vugt wrote: >> On 8/2/24 04:21, Mario Limonciello wrote: >>> On 2/7/2024 03:51, Daniel Vetter wrote: >>>> On Wed, Feb 07, 2024 at 10:03:10AM +0800, Daniel van Vugt wrote: >>>>> On 6/2/24 23:41, Mario Limonciello wrote: >>>>>> On 2/6/2024 08:21, Daniel Vetter wrote: >>>>>>> On Tue, Feb 06, 2024 at 06:10:51PM +0800, Daniel van Vugt wrote: >>>>>>>> Until now, deferred console takeover only meant defer until there is >>>>>>>> output. But that risks stepping on the toes of userspace splash >>>>>>>> screens, >>>>>>>> as console messages may appear before the splash screen. So check the >>>>>>>> command line for the expectation of userspace splash and if present >>>>>>>> then >>>>>>>> extend the deferral until after the first switch. >>>>>>>> >>>>>>>> V2: Added Kconfig option instead of hard coding "splash". >>>>>>>> >>>>>>>> Closes: https://bugs.launchpad.net/bugs/1970069 >>>>>>>> Cc: Mario Limonciello >>>>>>>> Signed-off-by: Daniel van Vugt >>>>>>>> --- >>>>>>>> drivers/video/console/Kconfig | 13 +++ >>>>>>>> drivers/video/fbdev/core/fbcon.c | 38 >>>>>>>> ++-- >>>>>>>> 2 files changed, 49 insertions(+), 2 deletions(-) >>>>>>>> >>>>>>>> diff --git a/drivers/video/console/Kconfig >>>>>>>> b/drivers/video/console/Kconfig >>>>>>>> index bc31db6ef7..a6e371bfb4 100644 >>>>>>>> --- a/drivers/video/console/Kconfig >>>>>>>> +++ b/drivers/video/console/Kconfig >>>>>>>> @@ -138,6 +138,19 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>>>> by the firmware in place, rather then replacing the contents >>>>>>>> with a >>>>>>>> black screen as soon as fbcon loads. >>>>>>>> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>>>>>>> + string "Framebuffer Console Deferred Takeover Condition" >>>>>>>> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>>>> + default "splash" >>>>>>>> + help >>>>>>>> + If enabled this defers further the framebuffer console taking >>>>>>>> over >>>>>>>> + until the first console switch has occurred. And even then only >>>>>>>> if >>>>>>>> + text has been output, and only if the specified parameter is >>>>>>>> found >>>>>>>> + on the command line. This ensures fbcon does not interrupt >>>>>>>> userspace >>>>>>>> + splash screens such as Plymouth which may be yet to start >>>>>>>> rendering >>>>>>>> + at the time of the first console output. "splash" is the >>>>>>>> simplest >>>>>>>> + distro-agnostic condition for this that Plymouth checks for. >>>>>>> >>>>>>> Hm this seems a bit strange since a lot of complexity that no one needs, >>>>>>> also my impression is that it's rather distro specific how you want this >>>>>>> to work. So why not just a Kconfig option that lets you choose how much >>>>>>> you want to delay fbcon setup, with the following options: >>>>>>> >>>>>>> - no delay at all >>>>>>> - dely until first output from the console (which then works for distros >>>>>>> which set a log-level to suppress unwanted stuff) >>>>>>> - delay until first vt-switch. In that case I don't think we also need >>>>>>> to >>>>>>> delay for first output, since vt switch usually means you'll get >>>>>>> first >>>>>>> output right away (if it's a vt terminal) or you switch to a >>>>>>> different >&g
Re: [PATCH v2 2/2] fbcon: Defer console takeover for splash screens to first switch
On 8/2/24 04:21, Mario Limonciello wrote: > On 2/7/2024 03:51, Daniel Vetter wrote: >> On Wed, Feb 07, 2024 at 10:03:10AM +0800, Daniel van Vugt wrote: >>> On 6/2/24 23:41, Mario Limonciello wrote: >>>> On 2/6/2024 08:21, Daniel Vetter wrote: >>>>> On Tue, Feb 06, 2024 at 06:10:51PM +0800, Daniel van Vugt wrote: >>>>>> Until now, deferred console takeover only meant defer until there is >>>>>> output. But that risks stepping on the toes of userspace splash screens, >>>>>> as console messages may appear before the splash screen. So check the >>>>>> command line for the expectation of userspace splash and if present then >>>>>> extend the deferral until after the first switch. >>>>>> >>>>>> V2: Added Kconfig option instead of hard coding "splash". >>>>>> >>>>>> Closes: https://bugs.launchpad.net/bugs/1970069 >>>>>> Cc: Mario Limonciello >>>>>> Signed-off-by: Daniel van Vugt >>>>>> --- >>>>>> drivers/video/console/Kconfig | 13 +++ >>>>>> drivers/video/fbdev/core/fbcon.c | 38 ++-- >>>>>> 2 files changed, 49 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/drivers/video/console/Kconfig >>>>>> b/drivers/video/console/Kconfig >>>>>> index bc31db6ef7..a6e371bfb4 100644 >>>>>> --- a/drivers/video/console/Kconfig >>>>>> +++ b/drivers/video/console/Kconfig >>>>>> @@ -138,6 +138,19 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>> by the firmware in place, rather then replacing the contents >>>>>> with a >>>>>> black screen as soon as fbcon loads. >>>>>> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>>>>> + string "Framebuffer Console Deferred Takeover Condition" >>>>>> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>> + default "splash" >>>>>> + help >>>>>> + If enabled this defers further the framebuffer console taking over >>>>>> + until the first console switch has occurred. And even then only if >>>>>> + text has been output, and only if the specified parameter is found >>>>>> + on the command line. This ensures fbcon does not interrupt >>>>>> userspace >>>>>> + splash screens such as Plymouth which may be yet to start >>>>>> rendering >>>>>> + at the time of the first console output. "splash" is the simplest >>>>>> + distro-agnostic condition for this that Plymouth checks for. >>>>> >>>>> Hm this seems a bit strange since a lot of complexity that no one needs, >>>>> also my impression is that it's rather distro specific how you want this >>>>> to work. So why not just a Kconfig option that lets you choose how much >>>>> you want to delay fbcon setup, with the following options: >>>>> >>>>> - no delay at all >>>>> - dely until first output from the console (which then works for distros >>>>> which set a log-level to suppress unwanted stuff) >>>>> - delay until first vt-switch. In that case I don't think we also need to >>>>> delay for first output, since vt switch usually means you'll get first >>>>> output right away (if it's a vt terminal) or you switch to a different >>>>> graphical console (which will keep fbcon fully suppressed on the drm >>>>> side). >>>>> >>> >>> I had similar thoughts, and had prototyped some of this already. But in the >>> end >>> it felt like extra complexity there was no demand for. >> >> For me this one is a bit too complex, since if you enable the vt switch >> delay you also get the output delay on top. That seems one too much and I >> can't come up with a use-case where you actually want that. So just a >> choice of one or the other or none feels cleaner. Remember the output "delay" goes to zero if any putc has occurred prior to registration (see dummycon.c). My current reason for using both is that in theory it prevents fbcon from taking over *earlier* than it did before, in case there was never any output. But I don't think there
Re: [PATCH v2 2/2] fbcon: Defer console takeover for splash screens to first switch
On 6/2/24 23:41, Mario Limonciello wrote: > On 2/6/2024 08:21, Daniel Vetter wrote: >> On Tue, Feb 06, 2024 at 06:10:51PM +0800, Daniel van Vugt wrote: >>> Until now, deferred console takeover only meant defer until there is >>> output. But that risks stepping on the toes of userspace splash screens, >>> as console messages may appear before the splash screen. So check the >>> command line for the expectation of userspace splash and if present then >>> extend the deferral until after the first switch. >>> >>> V2: Added Kconfig option instead of hard coding "splash". >>> >>> Closes: https://bugs.launchpad.net/bugs/1970069 >>> Cc: Mario Limonciello >>> Signed-off-by: Daniel van Vugt >>> --- >>> drivers/video/console/Kconfig | 13 +++ >>> drivers/video/fbdev/core/fbcon.c | 38 ++-- >>> 2 files changed, 49 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig >>> index bc31db6ef7..a6e371bfb4 100644 >>> --- a/drivers/video/console/Kconfig >>> +++ b/drivers/video/console/Kconfig >>> @@ -138,6 +138,19 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>> by the firmware in place, rather then replacing the contents with a >>> black screen as soon as fbcon loads. >>> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>> + string "Framebuffer Console Deferred Takeover Condition" >>> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>> + default "splash" >>> + help >>> + If enabled this defers further the framebuffer console taking over >>> + until the first console switch has occurred. And even then only if >>> + text has been output, and only if the specified parameter is found >>> + on the command line. This ensures fbcon does not interrupt userspace >>> + splash screens such as Plymouth which may be yet to start rendering >>> + at the time of the first console output. "splash" is the simplest >>> + distro-agnostic condition for this that Plymouth checks for. >> >> Hm this seems a bit strange since a lot of complexity that no one needs, >> also my impression is that it's rather distro specific how you want this >> to work. So why not just a Kconfig option that lets you choose how much >> you want to delay fbcon setup, with the following options: >> >> - no delay at all >> - dely until first output from the console (which then works for distros >> which set a log-level to suppress unwanted stuff) >> - delay until first vt-switch. In that case I don't think we also need to >> delay for first output, since vt switch usually means you'll get first >> output right away (if it's a vt terminal) or you switch to a different >> graphical console (which will keep fbcon fully suppressed on the drm >> side). >> I had similar thoughts, and had prototyped some of this already. But in the end it felt like extra complexity there was no demand for. If you would like to specify the preferred Kconfig design then I can implement it. Though I don't think there is an enumeration type. It could also be a runtime enumeration (deferred_takeover) controlled by fbcon=something. > > IIUC there is an "automatic" VT switch that happens with Ubuntu GRUB + Ubuntu > kernels. > > Why? > > Couldn't this also be suppressed by just not doing that? I have not seen any automatic VT switches in debugging but now that you mention it I was probably only debugging on drm-misc-next and not an Ubuntu kernel. - Daniel > >> I think you could even reuse the existing >> CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER for this, and then just >> compile-time select which kind of notifier to register (well plus the >> check for "splash" on the cmdline for the vt switch one I guess). >> >> Thoughts? >> >> Cheers, Sima >> >> >>> + >>> config STI_CONSOLE >>> bool "STI text console" >>> depends on PARISC && HAS_IOMEM >>> diff --git a/drivers/video/fbdev/core/fbcon.c >>> b/drivers/video/fbdev/core/fbcon.c >>> index 63af6ab034..98155d2256 100644 >>> --- a/drivers/video/fbdev/core/fbcon.c >>> +++ b/drivers/video/fbdev/core/fbcon.c >>> @@ -76,6 +76,7 @@ >>> #include /* For counting font checksums */ >>> #include >>> #include >>> +#include >>> #inclu
[PATCH v2 2/2] fbcon: Defer console takeover for splash screens to first switch
Until now, deferred console takeover only meant defer until there is
output. But that risks stepping on the toes of userspace splash screens,
as console messages may appear before the splash screen. So check the
command line for the expectation of userspace splash and if present then
extend the deferral until after the first switch.
V2: Added Kconfig option instead of hard coding "splash".
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello
Signed-off-by: Daniel van Vugt
---
drivers/video/console/Kconfig| 13 +++
drivers/video/fbdev/core/fbcon.c | 38 ++--
2 files changed, 49 insertions(+), 2 deletions(-)
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index bc31db6ef7..a6e371bfb4 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -138,6 +138,19 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
by the firmware in place, rather then replacing the contents with a
black screen as soon as fbcon loads.
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ string "Framebuffer Console Deferred Takeover Condition"
+ depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+ default "splash"
+ help
+ If enabled this defers further the framebuffer console taking over
+ until the first console switch has occurred. And even then only if
+ text has been output, and only if the specified parameter is found
+ on the command line. This ensures fbcon does not interrupt userspace
+ splash screens such as Plymouth which may be yet to start rendering
+ at the time of the first console output. "splash" is the simplest
+ distro-agnostic condition for this that Plymouth checks for.
+
config STI_CONSOLE
bool "STI text console"
depends on PARISC && HAS_IOMEM
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 63af6ab034..98155d2256 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -76,6 +76,7 @@
#include /* For counting font checksums */
#include
#include
+#include
#include "fbcon.h"
#include "fb_internal.h"
@@ -3358,6 +3359,26 @@ static int fbcon_output_notifier(struct notifier_block
*nb,
return NOTIFY_OK;
}
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+static int initial_console;
+static struct notifier_block fbcon_switch_nb;
+
+static int fbcon_switch_notifier(struct notifier_block *nb,
+unsigned long action, void *data)
+{
+ struct vc_data *vc = data;
+
+ WARN_CONSOLE_UNLOCKED();
+
+ if (vc->vc_num != initial_console) {
+ dummycon_unregister_switch_notifier(_switch_nb);
+ dummycon_register_output_notifier(_output_nb);
+ }
+
+ return NOTIFY_OK;
+}
+#endif
#endif
static void fbcon_start(void)
@@ -3370,7 +3391,16 @@ static void fbcon_start(void)
if (deferred_takeover) {
fbcon_output_nb.notifier_call = fbcon_output_notifier;
- dummycon_register_output_notifier(_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ if (cmdline_find_option_bool(boot_command_line,
+ CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
+ initial_console = fg_console;
+ fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
+ dummycon_register_switch_notifier(_switch_nb);
+ } else
+#endif
+ dummycon_register_output_notifier(_output_nb);
+
return;
}
#endif
@@ -3417,8 +3447,12 @@ void __exit fb_console_exit(void)
{
#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
console_lock();
- if (deferred_takeover)
+ if (deferred_takeover) {
dummycon_unregister_output_notifier(_output_nb);
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
+ dummycon_unregister_switch_notifier(_switch_nb);
+#endif
+ }
console_unlock();
cancel_work_sync(_deferred_takeover_work);
--
2.43.0
[PATCH v2 1/2] dummycon: Add dummycon_(un)register_switch_notifier
To detect switch attempts before a real console exists. This will be
used for the same purpose as dummycon_(un)register_output_notifier,
for fbcon to detect a more polite time to take over.
Signed-off-by: Daniel van Vugt
---
drivers/video/console/dummycon.c | 35 +++-
include/linux/console.h | 2 ++
2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 14af5d9e13..55e9b600ce 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -83,6 +83,32 @@ static int dummycon_blank(struct vc_data *vc, int blank, int
mode_switch)
/* Redraw, so that we get putc(s) for output done while blanked */
return 1;
}
+
+/* This is protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_switch_nh);
+
+void dummycon_register_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_register(_switch_nh, nb);
+}
+
+void dummycon_unregister_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_unregister(_switch_nh, nb);
+}
+
+static int dummycon_switch(struct vc_data *vc)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_call_chain(_switch_nh, 0, vc);
+
+ return 0;
+}
#else
static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
@@ -91,6 +117,10 @@ static int dummycon_blank(struct vc_data *vc, int blank,
int mode_switch)
{
return 0;
}
+static int dummycon_switch(struct vc_data *vc)
+{
+ return 0;
+}
#endif
static const char *dummycon_startup(void)
@@ -120,11 +150,6 @@ static bool dummycon_scroll(struct vc_data *vc, unsigned
int top,
return false;
}
-static int dummycon_switch(struct vc_data *vc)
-{
- return 0;
-}
-
/*
* The console `switch' structure for the dummy console
*
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8..8fd70ae623 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -531,5 +531,7 @@ extern void console_init(void);
/* For deferred console takeover */
void dummycon_register_output_notifier(struct notifier_block *nb);
void dummycon_unregister_output_notifier(struct notifier_block *nb);
+void dummycon_register_switch_notifier(struct notifier_block *nb);
+void dummycon_unregister_switch_notifier(struct notifier_block *nb);
#endif /* _LINUX_CONSOLE_H */
--
2.43.0
[PATCH 1/2] dummycon: Add dummycon_(un)register_switch_notifier
To detect switch attempts before a real console exists. This will be
used for the same purpose as dummycon_(un)register_output_notifier,
for fbcon to detect a more polite time to take over.
Signed-off-by: Daniel van Vugt
---
drivers/video/console/dummycon.c | 35 +++-
include/linux/console.h | 2 ++
2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 14af5d9e13..55e9b600ce 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -83,6 +83,32 @@ static int dummycon_blank(struct vc_data *vc, int blank, int
mode_switch)
/* Redraw, so that we get putc(s) for output done while blanked */
return 1;
}
+
+/* This is protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_switch_nh);
+
+void dummycon_register_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_register(_switch_nh, nb);
+}
+
+void dummycon_unregister_switch_notifier(struct notifier_block *nb)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_chain_unregister(_switch_nh, nb);
+}
+
+static int dummycon_switch(struct vc_data *vc)
+{
+ WARN_CONSOLE_UNLOCKED();
+
+ raw_notifier_call_chain(_switch_nh, 0, vc);
+
+ return 0;
+}
#else
static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
@@ -91,6 +117,10 @@ static int dummycon_blank(struct vc_data *vc, int blank,
int mode_switch)
{
return 0;
}
+static int dummycon_switch(struct vc_data *vc)
+{
+ return 0;
+}
#endif
static const char *dummycon_startup(void)
@@ -120,11 +150,6 @@ static bool dummycon_scroll(struct vc_data *vc, unsigned
int top,
return false;
}
-static int dummycon_switch(struct vc_data *vc)
-{
- return 0;
-}
-
/*
* The console `switch' structure for the dummy console
*
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8..8fd70ae623 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -531,5 +531,7 @@ extern void console_init(void);
/* For deferred console takeover */
void dummycon_register_output_notifier(struct notifier_block *nb);
void dummycon_unregister_output_notifier(struct notifier_block *nb);
+void dummycon_register_switch_notifier(struct notifier_block *nb);
+void dummycon_unregister_switch_notifier(struct notifier_block *nb);
#endif /* _LINUX_CONSOLE_H */
--
2.43.0
[PATCH 2/2] fbcon: Defer console takeover for splash screens to first switch
Until now, deferred console takeover only meant defer until there is
output. But that risks stepping on the toes of userspace splash screens,
as console messages may appear before the splash screen. So check for the
"splash" parameter (as used by Plymouth) and if present then extend the
deferral until the first switch.
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello
Signed-off-by: Daniel van Vugt
---
drivers/video/fbdev/core/fbcon.c | 32 +---
1 file changed, 29 insertions(+), 3 deletions(-)
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 63af6ab034..5b9f7635f7 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -76,6 +76,7 @@
#include /* For counting font checksums */
#include
#include
+#include
#include "fbcon.h"
#include "fb_internal.h"
@@ -146,6 +147,7 @@ static inline void fbcon_map_override(void)
#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
static bool deferred_takeover = true;
+static int initial_console = -1;
#else
#define deferred_takeover false
#endif
@@ -3341,7 +3343,7 @@ static void fbcon_register_existing_fbs(struct
work_struct *work)
console_unlock();
}
-static struct notifier_block fbcon_output_nb;
+static struct notifier_block fbcon_output_nb, fbcon_switch_nb;
static DECLARE_WORK(fbcon_deferred_takeover_work, fbcon_register_existing_fbs);
static int fbcon_output_notifier(struct notifier_block *nb,
@@ -3358,6 +3360,21 @@ static int fbcon_output_notifier(struct notifier_block
*nb,
return NOTIFY_OK;
}
+
+static int fbcon_switch_notifier(struct notifier_block *nb,
+unsigned long action, void *data)
+{
+ struct vc_data *vc = data;
+
+ WARN_CONSOLE_UNLOCKED();
+
+ if (vc->vc_num != initial_console) {
+ dummycon_unregister_switch_notifier(_switch_nb);
+ dummycon_register_output_notifier(_output_nb);
+ }
+
+ return NOTIFY_OK;
+}
#endif
static void fbcon_start(void)
@@ -3370,7 +3387,14 @@ static void fbcon_start(void)
if (deferred_takeover) {
fbcon_output_nb.notifier_call = fbcon_output_notifier;
- dummycon_register_output_notifier(_output_nb);
+ fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
+ initial_console = fg_console;
+
+ if (cmdline_find_option_bool(boot_command_line, "splash"))
+ dummycon_register_switch_notifier(_switch_nb);
+ else
+ dummycon_register_output_notifier(_output_nb);
+
return;
}
#endif
@@ -3417,8 +3441,10 @@ void __exit fb_console_exit(void)
{
#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
console_lock();
- if (deferred_takeover)
+ if (deferred_takeover) {
dummycon_unregister_output_notifier(_output_nb);
+ dummycon_unregister_switch_notifier(_switch_nb);
+ }
console_unlock();
cancel_work_sync(_deferred_takeover_work);
--
2.43.0
