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    Subject[PATCH v4 18/32] tty: Add ldisc hangup debug messages
    Date
    Expected typical debug log:
    [ 582.721965] tty_open: opening pts3...
    [ 582.721970] tty_open: opening pts3...
    [ 582.721977] tty_release: pts3 (tty count=3)...
    [ 582.721980] tty_release: ptm3 (tty count=1)...
    [ 582.722015] pts3 vhangup...
    [ 582.722020] tty_ldisc_hangup: pts3: closing ldisc: ffff88007a920540
    [ 582.724128] tty_release: pts3 (tty count=2)...
    [ 582.724217] tty_ldisc_hangup: pts3: re-opened ldisc: ffff88007a920580
    [ 582.724221] tty_release: ptm3: final close
    [ 582.724234] tty_ldisc_release: ptm3: closing ldisc: ffff88007a920a80
    [ 582.724238] tty_ldisc_release: ptm3: ldisc closed
    [ 582.724241] tty_release: ptm3: freeing structure...
    [ 582.724741] tty_open: opening pts3...

    Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
    ---
    drivers/tty/tty_ldisc.c | 19 +++++++++++++++++++
    1 file changed, 19 insertions(+)

    diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
    index 0030d55..328ff5b 100644
    --- a/drivers/tty/tty_ldisc.c
    +++ b/drivers/tty/tty_ldisc.c
    @@ -20,6 +20,17 @@
    #include <linux/uaccess.h>
    #include <linux/ratelimit.h>

    +#undef LDISC_DEBUG_HANGUP
    +
    +#ifdef LDISC_DEBUG_HANGUP
    +#define tty_ldisc_debug(tty, f, args...) ({ \
    + char __b[64]; \
    + printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
    +})
    +#else
    +#define tty_ldisc_debug(tty, f, args...)
    +#endif
    +
    /*
    * This guards the refcounted line discipline lists. The lock
    * must be taken with irqs off because there are hangup path
    @@ -822,6 +833,8 @@ void tty_ldisc_hangup(struct tty_struct *tty)
    int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
    int err = 0;

    + tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
    +
    /*
    * FIXME! What are the locking issues here? This may me overdoing
    * things... This question is especially important now that we've
    @@ -878,6 +891,8 @@ void tty_ldisc_hangup(struct tty_struct *tty)
    mutex_unlock(&tty->ldisc_mutex);
    if (reset)
    tty_reset_termios(tty);
    +
    + tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc);
    }

    /**
    @@ -944,6 +959,8 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
    * it does not race with the set_ldisc code path.
    */

    + tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
    +
    tty_ldisc_halt(tty, o_tty, MAX_SCHEDULE_TIMEOUT);

    tty_lock_pair(tty, o_tty);
    @@ -955,6 +972,8 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
    tty_unlock_pair(tty, o_tty);
    /* And the memory resources remaining (buffers, termios) will be
    disposed of when the kref hits zero */
    +
    + tty_ldisc_debug(tty, "ldisc closed\n");
    }

    /**
    --
    1.8.1.2


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