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Fix select/poll/kqueue for write on reverse direction before first write.

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The reverse direction of a pipe is lazily allocated on the first write in
that direction (because pipes are usually used in one direction only).  A
special case is needed to ensure the pipe appears writable before the first
write because there are 0 bytes of pending data in 0 bytes of buffer space
at that point, leaving 0 bytes of data that can be written with the normal
code.

Note that the first write returns [ENOMEM] if kern.ipc.maxpipekva is
exceeded and does not block or return [EAGAIN], so selecting true for write
is correct even in that case.

PR:		kern/93685
Submitted by:	gianni
MFC after:	2 weeks
This commit is contained in:
Jilles Tjoelker 2011-12-14 22:26:39 +00:00
parent fb680e16f4
commit 6d1c58f8a2
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=228510
1 changed files with 4 additions and 2 deletions
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6
sys/kern/sys_pipe.c
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@ -1349,7 +1349,8 @@ pipe_poll(fp, events, active_cred, td)
if (wpipe->pipe_present != PIPE_ACTIVE ||
(wpipe->pipe_state & PIPE_EOF) ||
(((wpipe->pipe_state & PIPE_DIRECTW) == 0) &&
(wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF))
((wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF ||
wpipe->pipe_buffer.size == 0)))
revents |= events & (POLLOUT | POLLWRNORM);
if ((events & POLLINIGNEOF) == 0) {
@ -1660,7 +1661,8 @@ filt_pipewrite(struct knote *kn, long hint)
PIPE_UNLOCK(rpipe);
return (1);
}
kn->kn_data = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
kn->kn_data = (wpipe->pipe_buffer.size > 0) ?
(wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) : PIPE_BUF;
if (wpipe->pipe_state & PIPE_DIRECTW)
kn->kn_data = 0;