Author: jilles
Date: Wed Dec 14 22:26:39 2011
New Revision: 228510
URL: http://svn.freebsd.org/changeset/base/228510
Log:
Fix select/poll/kqueue for write on reverse direction before first write.
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
Modified:
head/sys/kern/sys_pipe.c
Modified: head/sys/kern/sys_pipe.c
==============================================================================
--- head/sys/kern/sys_pipe.c Wed Dec 14 22:22:19 2011 (r228509)
+++ head/sys/kern/sys_pipe.c Wed Dec 14 22:26:39 2011 (r228510)
@@ -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 hi
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;
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