linux-toradex.git/include/linux/poll.h, branch v4.5

UAPI: (Scripted) Disintegrate include/linux

2012-10-13T09:46:48+00:00

Signed-off-by: David Howells 
Acked-by: Arnd Bergmann 
Acked-by: Thomas Gleixner 
Acked-by: Michael Kerrisk 
Acked-by: Paul E. McKenney 
Acked-by: Dave Jones

poll: add poll_requested_events() and poll_does_not_wait() functions

2012-03-23T23:58:38+00:00

In some cases the poll() implementation in a driver has to do different
things depending on the events the caller wants to poll for.  An example
is when a driver needs to start a DMA engine if the caller polls for
POLLIN, but doesn't want to do that if POLLIN is not requested but instead
only POLLOUT or POLLPRI is requested.  This is something that can happen
in the video4linux subsystem among others.

Unfortunately, the current epoll/poll/select implementation doesn't
provide that information reliably.  The poll_table_struct does have it: it
has a key field with the event mask.  But once a poll() call matches one
or more bits of that mask any following poll() calls are passed a NULL
poll_table pointer.

Also, the eventpoll implementation always left the key field at ~0 instead
of using the requested events mask.

This was changed in eventpoll.c so the key field now contains the actual
events that should be polled for as set by the caller.

The solution to the NULL poll_table pointer is to set the qproc field to
NULL in poll_table once poll() matches the events, not the poll_table
pointer itself.  That way drivers can obtain the mask through a new
poll_requested_events inline.

The poll_table_struct can still be NULL since some kernel code calls it
internally (netfs_state_poll() in ./drivers/staging/pohmelfs/netfs.h).  In
that case poll_requested_events() returns ~0 (i.e.  all events).

Very rarely drivers might want to know whether poll_wait will actually
wait.  If another earlier file descriptor in the set already matched the
events the caller wanted to wait for, then the kernel will return from the
select() call without waiting.  This might be useful information in order
to avoid doing expensive work.

A new helper function poll_does_not_wait() is added that drivers can use
to detect this situation.  This is now used in sock_poll_wait() in
include/net/sock.h.  This was the only place in the kernel that needed
this information.

Drivers should no longer access any of the poll_table internals, but use
the poll_requested_events() and poll_does_not_wait() access functions
instead.  In order to enforce that the poll_table fields are now prepended
with an underscore and a comment was added warning against using them
directly.

This required a change in unix_dgram_poll() in unix/af_unix.c which used
the key field to get the requested events.  It's been replaced by a call
to poll_requested_events().

For qproc it was especially important to change its name since the
behavior of that field changes with this patch since this function pointer
can now be NULL when that wasn't possible in the past.

Any driver accessing the qproc or key fields directly will now fail to compile.

Some notes regarding the correctness of this patch: the driver's poll()
function is called with a 'struct poll_table_struct *wait' argument.  This
pointer may or may not be NULL, drivers can never rely on it being one or
the other as that depends on whether or not an earlier file descriptor in
the select()'s fdset matched the requested events.

There are only three things a driver can do with the wait argument:

1) obtain the key field:

	events = wait ? wait->key : ~0;

   This will still work although it should be replaced with the new
   poll_requested_events() function (which does exactly the same).
   This will now even work better, since wait is no longer set to NULL
   unnecessarily.

2) use the qproc callback. This could be deadly since qproc can now be
   NULL. Renaming qproc should prevent this from happening. There are no
   kernel drivers that actually access this callback directly, BTW.

3) test whether wait == NULL to determine whether poll would return without
   waiting. This is no longer sufficient as the correct test is now
   wait == NULL || wait->_qproc == NULL.

   However, the worst that can happen here is a slight performance hit in
   the case where wait != NULL and wait->_qproc == NULL. In that case the
   driver will assume that poll_wait() will actually add the fd to the set
   of waiting file descriptors. Of course, poll_wait() will not do that
   since it tests for wait->_qproc. This will not break anything, though.

   There is only one place in the whole kernel where this happens
   (sock_poll_wait() in include/net/sock.h) and that code will be replaced
   by a call to poll_does_not_wait() in the next patch.

   Note that even if wait->_qproc != NULL drivers cannot rely on poll_wait()
   actually waiting. The next file descriptor from the set might match the
   event mask and thus any possible waits will never happen.

Signed-off-by: Hans Verkuil 
Reviewed-by: Jonathan Corbet 
Reviewed-by: Al Viro 
Cc: Davide Libenzi 
Signed-off-by: Hans de Goede 
Cc: Mauro Carvalho Chehab 
Cc: David Miller 
Cc: Eric Dumazet 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Fix common misspellings

2011-03-31T14:26:23+00:00

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi

poll: fix a typo in comment

2010-12-10T14:06:43+00:00

Convert duplicated sys_poll to select. As Kosaki suggests, sys_poll() and
sys_select() are now hidden by SYSCALL_DEFINEx() macros so it would be
better to use plain select/poll syscall name.

Signed-off-by: Namhyung Kim 
Reviewed-by: KOSAKI Motohiro 
Signed-off-by: Jiri Kosina

epoll: make epoll_wait() use the hrtimer range feature

2010-10-28T01:03:18+00:00

This make epoll use hrtimers for the timeout value which prevents
epoll_wait() from timing out up to a millisecond early.

This mirrors the behavior of select() and poll().

Signed-off-by: Shawn Bohrer 
Cc: Al Viro 
Acked-by: Davide Libenzi 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

sysctl extern cleanup: poll

2010-03-12T23:53:11+00:00

Extern declarations in sysctl.c should be moved to their own header file,
and then include them in relavant .c files.

Move epoll_table extern declaration to linux/poll.h

Signed-off-by: Dave Young 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

headers: remove sched.h from poll.h

2009-10-04T22:05:10+00:00

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

poll: avoid extra wakeups in select/poll

2009-06-17T02:47:48+00:00

After introduction of keyed wakeups Davide Libenzi did on epoll, we are
able to avoid spurious wakeups in poll()/select() code too.

For example, typical use of poll()/select() is to wait for incoming
network frames on many sockets.  But TX completion for UDP/TCP frames call
sock_wfree() which in turn schedules thread.

When scheduled, thread does a full scan of all polled fds and can sleep
again, because nothing is really available.  If number of fds is large,
this cause significant load.

This patch makes select()/poll() aware of keyed wakeups and useless
wakeups are avoided.  This reduces number of context switches by about 50%
on some setups, and work performed by sofirq handlers.

Signed-off-by: Eric Dumazet 
Acked-by: David S. Miller 
Acked-by: Andi Kleen 
Acked-by: Ingo Molnar 
Acked-by: Davide Libenzi 
Cc: Christoph Lameter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

poll: allow f_op->poll to sleep

2009-01-06T23:59:12+00:00

f_op->poll is the only vfs operation which is not allowed to sleep.  It's
because poll and select implementation used task state to synchronize
against wake ups, which doesn't have to be the case anymore as wait/wake
interface can now use custom wake up functions.  The non-sleep restriction
can be a bit tricky because ->poll is not called from an atomic context
and the result of accidentally sleeping in ->poll only shows up as
temporary busy looping when the timing is right or rather wrong.

This patch converts poll/select to use custom wake up function and use
separate triggered variable to synchronize against wake up events.  The
only added overhead is an extra function call during wake up and
negligible.

This patch removes the one non-sleep exception from vfs locking rules and
is beneficial to userland filesystem implementations like FUSE, 9p or
peculiar fs like spufs as it's very difficult for those to implement
non-sleeping poll method.

While at it, make the following cosmetic changes to make poll.h and
select.c checkpatch friendly.

* s/type * symbol/type *symbol/		   : three places in poll.h
* remove blank line before EXPORT_SYMBOL() : two places in select.c

Oleg: spotted missing barrier in poll_schedule_timeout()
Davide: spotted missing write barrier in pollwake()

Signed-off-by: Tejun Heo 
Cc: Eric Van Hensbergen 
Cc: Ron Minnich 
Cc: Ingo Molnar 
Cc: Christoph Hellwig 
Signed-off-by: Miklos Szeredi 
Cc: Davide Libenzi 
Cc: Brad Boyer 
Cc: Al Viro 
Cc: Roland McGrath 
Cc: Mauro Carvalho Chehab 
Signed-off-by: Andrew Morton 
Cc: Davide Libenzi 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

select: switch select() and poll() over to hrtimers

2008-09-06T04:35:03+00:00

With lots of help, input and cleanups from Thomas Gleixner

This patch switches select() and poll() over to hrtimers.

The core of the patch is replacing the "s64 timeout" with a
"struct timespec end_time" in all the plumbing.

But most of the diffstat comes from using the just introduced helpers:
	poll_select_set_timeout
	poll_select_copy_remaining
	timespec_add_safe
which make manipulating the timespec easier and less error-prone.

Signed-off-by: Arjan van de Ven 
Signed-off-by: Thomas Gleixner