linux.git/drivers/char/pty.c, branch v2.6.31

pty: don't limit the writes to 'pty_space()' inside 'pty_write()'

2009-09-05T20:27:10+00:00

The whole write-room thing is something that is up to the _caller_ to
worry about, not the pty layer itself.  The total buffer space will
still be limited by the buffering routines themselves, so there is no
advantage or need in having pty_write() artificially limit the size
somehow.

And what happened was that the caller (the n_tty line discipline, in
this case) may have verified that there is room for 2 bytes to be
written (for NL -> CRNL expansion), and it used to then do those writes
as two single-byte writes.  And if the first byte written (CR) then
caused a new tty buffer to be allocated, pty_space() may have returned
zero when trying to write the second byte (LF), and then incorrectly
failed the write - leading to a lost newline character.

This should finally fix

	http://bugzilla.kernel.org/show_bug.cgi?id=14015

Reported-by: Mikael Pettersson 
Acked-by: Alan Cox 
Signed-off-by: Linus Torvalds

pty: fix data loss when stopped (^S/^Q)

2009-08-10T20:31:18+00:00

Commit d945cb9cc ("pty: Rework the pty layer to use the normal buffering
logic") dropped the test for 'tty->stopped' in pty_write_room(), which
then causes the n_tty line discipline thing to not throttle the data
properly when the tty is stopped.

So instead of pausing the write due to the tty being stopped, the ldisc
layer would go ahead and push it down to the pty.  The pty write()
routine would then refuse to take the data (because it _did_ check
'stopped'), and the data wouldn't actually be written.

This whole stopped test should eventually be moved into the tty ldisc
layer rather than have low-level tty drivers care about these things,
but right now the fix is to just re-instate the missing pty 'stopped'
handling.

Reported-and-tested-by: Artur Skawina 
Cc: Alan Cox 
Signed-off-by: Linus Torvalds

pty: avoid forcing 'low_latency' tty flag

2009-07-29T19:15:56+00:00

We really don't want to mark the pty as a low-latency device, because as
Alan points out, the ->write method can be called from an IRQ (ppp?),
and that means we can't use ->low_latency=1 as we take mutexes in the
low_latency case.

So rather than using low_latency to force the written data to be pushed
to the ldisc handling at 'write()' time, just make the reader side (or
the poll function) do the flush when it checks whether there is data to
be had.

This also fixes the problem with lost data in an emacs compile buffer
(bugzilla 13815), and we can thus revert the low_latency pty hack
(commit 3a54297478e6578f96fd54bf4daa1751130aca86: "pty: quickfix for the
pty ENXIO timing problems").

Signed-off-by: OGAWA Hirofumi 
Tested-by: Aneesh Kumar K.V 
[ Modified to do the tty_flush_to_ldisc() inside input_available_p() so
  that it triggers for both read and poll()  - Linus]
Signed-off-by: Linus Torvalds

pty: quickfix for the pty ENXIO timing problems

2009-07-27T22:53:29+00:00

This also makes close stall in the normal case which is apparently
needed to fix emacs

Signed-off-by: Alan Cox 
Signed-off-by: Linus Torvalds

headers: smp_lock.h redux

2009-07-12T19:22:34+00:00

* Remove smp_lock.h from files which don't need it (including some headers!)
* Add smp_lock.h to files which do need it
* Make smp_lock.h include conditional in hardirq.h
  It's needed only for one kernel_locked() usage which is under CONFIG_PREEMPT

  This will make hardirq.h inclusion cheaper for every PREEMPT=n config
  (which includes allmodconfig/allyesconfig, BTW)

Signed-off-by: Alexey Dobriyan 
Signed-off-by: Linus Torvalds

pty: Rework the pty layer to use the normal buffering logic

2009-07-08T16:47:59+00:00

This fixes the ppp problems and various other issues with call locking
caused by one side of a pty called in one locking context trying to match
another with differing rules on the other side. We also get a big slack
space to work with that means we can bury the flow control deadlock case
for any conceivable real world situation.

Signed-off-by: Alan Cox 
Signed-off-by: Linus Torvalds

pty: Narrow the race on ldisc locking

2009-06-16T19:01:16+00:00

The pty code has always been buggy on its ldisc handling. The recent
changes made the window for the race much bigger. Pending fixing it
properly which is not at all trivial, at least make the race small again so
we don't disrupt other dev work.

Signed-off-by: Alan Cox 
Signed-off-by: Linus Torvalds

tty: rewrite the ldisc locking

2009-06-11T15:51:01+00:00

There are several pretty much unfixable races in the old ldisc code, especially
with respect to pty behaviour and also to hangup. It's easier to rewrite the
code than simply try and patch it up.

This patch
- splits the ldisc from the tty (so we will be able to refcount it more cleanly
  later)
- introduces a mutex lock for ldisc changing on an active device
- fixes the complete mess that hangup caused
- implements hopefully correct setldisc/close/hangup locking

There are still some problems around pty pairs that have always been there but
at least it is now possible to understand the code and fix further problems.

This fixes the following known bugs
- hang up can leak ldisc references
- hang up may not call open/close on ldisc in a matched way
- pty/tty pairs can deadlock during an ldisc change
- reading the ldisc proc files can cause every ldisc to be loaded

and probably a few other of the mysterious ldisc race reports.

I'm sure it also adds the odd new one.

Signed-off-by: Alan Cox 
Signed-off-by: Linus Torvalds

pty: Fix a comment

2009-06-11T15:51:00+00:00

We fixed the globals, so now fix the comment

Signed-off-by: Alan Cox 
Signed-off-by: Linus Torvalds

pty: Fix documentation

2009-01-13T00:37:00+00:00

The pty changes and updates for window sizing forgot to correct the
kerneldoc

Signed-off-by: Alan Cox 
Signed-off-by: Linus Torvalds