On 02/16/2015 08:04 AM, Peter Hurley wrote:
> On 02/05/2015 02:11 PM, Nan Li wrote:
>> This will greatly enhance the usefulness of QEMU virtual serial ports,
>> because the Linux kernel interprets a break on the serial console as a
>> SysRq, but there is currently no way to pass this signal over a
>> pseudo-terminal. This patch will work for transmitting BREAK from master to
>> slave through pseudo-terminal.
>
> pty is an IPC mechanism, not a virtualization driver.
>
> Those programs that know they're consuming from a slave pty may not
> have bothered to set termios for BREAKs, and may not be prepared
> for NULLs in the input stream.
I'm not even seeing how this works as advertised.
In QEMU, the *master* end is the source/sink for the guest VM, while the
*slave* pty is sink/source for the host. Like this:
Host <--> slave pty <===> master pty <--> qemu <==> emulated serial port
So this patch enables the guest VM to transmit BREAK to the host.
Why is that useful?
Regards,
Peter Hurley
>> Signed-off-by: Nan Li <n...@suse.com>
>> ---
>> drivers/tty/pty.c | 19 +++++++++++++++++++
>> 1 file changed, 19 insertions(+)
>>
>> diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
>> index e72ee62..ac8893a 100644
>> --- a/drivers/tty/pty.c
>> +++ b/drivers/tty/pty.c
>> @@ -31,6 +31,7 @@
>> static struct tty_driver *ptm_driver;
>> static struct tty_driver *pts_driver;
>> static DEFINE_MUTEX(devpts_mutex);
>> +#define BREAK_STRING '\0'
>> #endif
>>
>> static void pty_close(struct tty_struct *tty, struct file *filp)
>> @@ -674,6 +675,23 @@ static void pty_unix98_shutdown(struct tty_struct *tty)
>> devpts_kill_index(tty->driver_data, tty->index);
>> }
>>
>> +static int pty_unix98_break_ctl(struct tty_struct *tty, int break_state)
>> +{
>> + int c;
>> + struct tty_struct *to = tty->link;
>> +
>> + if (break_state) {
>> + /* Stuff the break data into the input queue of the other end */
>> + c = tty_insert_flip_char(to->port, BREAK_STRING, TTY_BREAK);
>> + /* And shovel */
>> + if (c)
>> + tty_flip_buffer_push(to->port);
>> + else
>> + return -ENOMEM;
>> + }
>> + return 0;
>> +}
>> +
>> static const struct tty_operations ptm_unix98_ops = {
>> .lookup = ptm_unix98_lookup,
>> .install = pty_unix98_install,
>> @@ -686,6 +704,7 @@ static const struct tty_operations ptm_unix98_ops = {
>> .chars_in_buffer = pty_chars_in_buffer,
>> .unthrottle = pty_unthrottle,
>> .ioctl = pty_unix98_ioctl,
>> + .break_ctl = pty_unix98_break_ctl,
>> .resize = pty_resize,
>> .shutdown = pty_unix98_shutdown,
>> .cleanup = pty_cleanup
>>
>
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