svn commit: r286307 - in head: lib/libc/sys sys/kern sys/sys

[Ed Schouten]

Author: ed
Date: Wed Aug  5 07:34:29 2015
New Revision: 286307
URL: https://svnweb.freebsd.org/changeset/base/286307

Log:
  Make it possible to implement poll(2) on top of kqueue(2).
  
  It looks like EVFILT_READ and EVFILT_WRITE trigger under the same
  conditions as poll()'s POLLRDNORM and POLLWRNORM as described by POSIX.
  The only difference is that POLLRDNORM has to be triggered on regular
  files unconditionally, whereas EVFILT_READ only triggers when not EOF.
  
  Introduce a new flag, NOTE_FILE_POLL, that can be used to make
  EVFILT_READ and EVFILT_WRITE behave identically to poll(). This flag
  will be used by cloudlibc's poll() function.
  
  Reviewed by:	jmg
  Differential Revision:	https://reviews.freebsd.org/D3303

Modified:
  head/lib/libc/sys/kqueue.2
  head/sys/kern/vfs_subr.c
  head/sys/sys/event.h

Modified: head/lib/libc/sys/kqueue.2
==============================================================================
--- head/lib/libc/sys/kqueue.2	Wed Aug  5 07:29:59 2015	(r286306)
+++ head/lib/libc/sys/kqueue.2	Wed Aug  5 07:34:29 2015	(r286307)
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 29, 2015
+.Dd August 4, 2015
 .Dt KQUEUE 2
 .Os
 .Sh NAME
@@ -288,6 +288,14 @@ Returns when the file pointer is not at 
 .Va data
 contains the offset from current position to end of file,
 and may be negative.
+.Pp
+This behavior is different from
+.Xr poll 2 ,
+where read events are triggered for regular files unconditionally.
+This event can be triggered unconditionally by setting the
+.Dv NOTE_FILE_POLL
+flag in
+.Va fflags .
 .It "Fifos, Pipes"
 Returns when the there is data to read;
 .Va data

Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c	Wed Aug  5 07:29:59 2015	(r286306)
+++ head/sys/kern/vfs_subr.c	Wed Aug  5 07:34:29 2015	(r286307)
@@ -4622,7 +4622,7 @@ filt_vfsread(struct knote *kn, long hint
 
 	VI_LOCK(vp);
 	kn->kn_data = va.va_size - kn->kn_fp->f_offset;
-	res = (kn->kn_data != 0);
+	res = (kn->kn_sfflags & NOTE_FILE_POLL) != 0 || kn->kn_data != 0;
 	VI_UNLOCK(vp);
 	return (res);
 }

Modified: head/sys/sys/event.h
==============================================================================
--- head/sys/sys/event.h	Wed Aug  5 07:29:59 2015	(r286306)
+++ head/sys/sys/event.h	Wed Aug  5 07:34:29 2015	(r286307)
@@ -108,6 +108,7 @@ struct kevent {
  * data/hint flags for EVFILT_{READ|WRITE}, shared with userspace
  */
 #define NOTE_LOWAT	0x0001			/* low water mark */
+#define NOTE_FILE_POLL	0x0002			/* behave like poll() */
 
 /*
  * data/hint flags for EVFILT_VNODE, shared with userspace