From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [patch 03/21] vfs: improve comment describing fget_light() Date: Fri, 18 Sep 2009 13:05:41 -0700 Message-ID: <200909182005.n8IK5fud019041@imap1.linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Cc: linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org, tonyb@cybernetics.com To: viro@zeniv.linux.org.uk Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:50620 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758147AbZIRUGA (ORCPT ); Fri, 18 Sep 2009 16:06:00 -0400 Sender: linux-fsdevel-owner@vger.kernel.org List-ID: From: Tony Battersby Improve the description of fget_light(), which is currently incorrect about needing a prior refcnt (judging by the way it is actually used). Signed-off-by: Tony Battersby Cc: Al Viro Signed-off-by: Andrew Morton --- fs/file_table.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff -puN fs/file_table.c~vfs-improve-comment-describing-fget_light fs/file_table.c --- a/fs/file_table.c~vfs-improve-comment-describing-fget_light +++ a/fs/file_table.c @@ -317,11 +317,20 @@ struct file *fget(unsigned int fd) EXPORT_SYMBOL(fget); /* - * Lightweight file lookup - no refcnt increment if fd table isn't shared. - * You can use this only if it is guranteed that the current task already - * holds a refcnt to that file. That check has to be done at fget() only - * and a flag is returned to be passed to the corresponding fput_light(). - * There must not be a cloning between an fget_light/fput_light pair. + * Lightweight file lookup - no refcnt increment if fd table isn't shared. + * + * You can use this instead of fget if you satisfy all of the following + * conditions: + * 1) You must call fput_light before exiting the syscall and returning control + * to userspace (i.e. you cannot remember the returned struct file * after + * returning to userspace). + * 2) You must not call filp_close on the returned struct file * in between + * calls to fget_light and fput_light. + * 3) You must not clone the current task in between the calls to fget_light + * and fput_light. + * + * The fput_needed flag returned by fget_light should be passed to the + * corresponding fput_light. */ struct file *fget_light(unsigned int fd, int *fput_needed) { _