svn commit: r349041 - head/lib/libc/sys

[Alan Somers]

Author: asomers
Date: Fri Jun 14 20:35:37 2019
New Revision: 349041
URL: https://svnweb.freebsd.org/changeset/base/349041

Log:
  open(2): fix the description of O_FSYNC
  
  The man page claims that with O_FSYNC (aka O_SYNC) the kernel will not cache
  written data. However, that's not true. Nor does POSIX require it.
  Perhaps it was true when that section of the man page was written in r69336
  (I haven't checked). But it's not true now.  Now the effect is simply that
  writes are sent to disk immediately and synchronously, but they're still
  cached.
  
  See also: https://pubs.opengroup.org/onlinepubs/9699919799/
  See also: ffs_write in sys/ufs/ffs/ffs_vnops.c
  
  Reviewed by:	cem
  MFC after:	2 weeks
  Sponsored by:	The FreeBSD Foundation
  Differential Revision:	https://reviews.freebsd.org/D20641

Modified:
  head/lib/libc/sys/open.2

Modified: head/lib/libc/sys/open.2
==============================================================================
--- head/lib/libc/sys/open.2	Fri Jun 14 20:04:28 2019	(r349040)
+++ head/lib/libc/sys/open.2	Fri Jun 14 20:35:37 2019	(r349041)
@@ -28,7 +28,7 @@
 .\"     @(#)open.2	8.2 (Berkeley) 11/16/93
 .\" $FreeBSD$
 .\"
-.Dd November 11, 2018
+.Dd June 14, 2019
 .Dt OPEN 2
 .Os
 .Sh NAME
@@ -224,10 +224,7 @@ The descriptor remains in non-blocking mode for subseq
 If
 .Dv O_FSYNC
 is used in the mask, all writes will
-immediately be written to disk,
-the kernel will not cache written data
-and all writes on the descriptor will not return until
-the data to be written completes.
+immediately and synchronously be written to disk.
 .Pp
 .Dv O_SYNC
 is a synonym for