On Tue, 17 Feb 2015 14:03:58 -0500 Peter Hurley <pe...@hurleysoftware.com> wrote:
> 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: Yes, you're totally right. This patch implements break handling on the "wrong" side of the pty pair. I think you have already pointed this out in one of the previous mails, and we're waiting for a patch that implements it on the slave side. Regards, Petr Tesarik > 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 > >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/