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Fix handling of EV_EOF for named pipes.

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Contrary to the kevent man page, EV_EOF on a fifo is not cleared by
EV_CLEAR.  Modify the read and write filters to clear EV_EOF when the
fifo's PIPE_EOF flag is clear, and update the man page to document the
new behaviour.

Modify the write filter to return the amount of buffer space available
even if no readers are present.  This matches the behaviour for sockets.

When reading from a pipe, only call pipeselwakeup() if some data was
actually read.  This prevents the continuous re-triggering of a
EVFILT_READ event on EOF when in edge-triggered mode.

PR:		203366, 224615
Submitted by:	Jan Kokemüller <jan.kokemueller@gmail.com>
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D24528
This commit is contained in:
Mark Johnston 2020-04-27 15:59:19 +00:00
parent 9b22722423
commit 569eb766c5
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=360380
2 changed files with 34 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
lib/libc/sys/kqueue.2
View File

@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd April 21, 2020
.Dd April 27, 2020
.Dt KQUEUE 2
.Os
.Sh NAME
@ -323,8 +323,7 @@ When the last writer disconnects, the filter will set
.Dv EV_EOF
in
.Va flags .
This may be cleared by passing in
.Dv EV_CLEAR ,
This will be cleared by the filter when a new writer connects,
at which point the
filter will resume waiting for data to become available before
returning.
@ -343,9 +342,10 @@ For sockets, pipes
and fifos,
.Va data
will contain the amount of space remaining in the write buffer.
The filter will set EV_EOF when the reader disconnects, and for
the fifo case, this may be cleared by use of
.Dv EV_CLEAR .
The filter will set
.Dv EV_EOF
when the reader disconnects, and for the fifo case, this will be cleared
when a new reader connects.
Note that this filter is not supported for vnodes or BPF devices.
.Pp
For sockets, the low water mark and socket error handling is

45
sys/kern/sys_pipe.c
View File

@ -824,7 +824,12 @@ pipe_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
}
}
if ((rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt) >= PIPE_BUF)
/*
* Only wake up writers if there was actually something read.
* Otherwise, when calling read(2) at EOF, a spurious wakeup occurs.
*/
if (nread > 0 &&
rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt >= PIPE_BUF)
pipeselwakeup(rpipe);
PIPE_UNLOCK(rpipe);
@ -1726,48 +1731,54 @@ filt_pipedetach(struct knote *kn)
static int
filt_piperead(struct knote *kn, long hint)
{
struct file *fp = kn->kn_fp;
struct pipe *rpipe = kn->kn_hook;
struct pipe *wpipe = rpipe->pipe_peer;
int ret;
PIPE_LOCK_ASSERT(rpipe, MA_OWNED);
kn->kn_data = rpipe->pipe_buffer.cnt;
if (kn->kn_data == 0)
kn->kn_data = rpipe->pipe_map.cnt;
if ((rpipe->pipe_state & PIPE_EOF) ||
wpipe->pipe_present != PIPE_ACTIVE ||
(wpipe->pipe_state & PIPE_EOF)) {
if ((rpipe->pipe_state & PIPE_EOF) != 0 &&
((rpipe->pipe_state & PIPE_NAMED) == 0 ||
fp->f_pipegen != rpipe->pipe_wgen)) {
kn->kn_flags |= EV_EOF;
return (1);
}
ret = kn->kn_data > 0;
return ret;
kn->kn_flags &= ~EV_EOF;
return (kn->kn_data > 0);
}
/*ARGSUSED*/
static int
filt_pipewrite(struct knote *kn, long hint)
{
struct pipe *wpipe;
struct pipe *wpipe = kn->kn_hook;
/*
* If this end of the pipe is closed, the knote was removed from the
* knlist and the list lock (i.e., the pipe lock) is therefore not held.
*/
wpipe = kn->kn_hook;
if (wpipe->pipe_present == PIPE_ACTIVE ||
(wpipe->pipe_state & PIPE_NAMED) != 0) {
PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
if (wpipe->pipe_state & PIPE_DIRECTW) {
kn->kn_data = 0;
} else if (wpipe->pipe_buffer.size > 0) {
kn->kn_data = wpipe->pipe_buffer.size -
wpipe->pipe_buffer.cnt;
} else {
kn->kn_data = PIPE_BUF;
}
}
if (wpipe->pipe_present != PIPE_ACTIVE ||
(wpipe->pipe_state & PIPE_EOF)) {
kn->kn_data = 0;
kn->kn_flags |= EV_EOF;
return (1);
}
PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
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;
kn->kn_flags &= ~EV_EOF;
return (kn->kn_data >= PIPE_BUF);
}