linux-kernel - [PATCH 02/25] rearrange may

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Message-Id: <20070920195250.7656557C@kernel>
Date:	Thu, 20 Sep 2007 12:52:50 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	akpm@...l.org
Cc:	linux-kernel@...r.kernel.org, hch@...radead.org,
	Dave Hansen <haveblue@...ibm.com>
Subject: [PATCH 02/25] rearrange may_open() to be r/o friendly

may_open() calls vfs_permission() before it does checks for
IS_RDONLY(inode).  It checks _again_ inside of vfs_permission().

The check inside of vfs_permission() is going away eventually.
With the mnt_want/drop_write() functions, all of the r/o
checks (except for this one) are consistently done before
calling permission().  Because of this, I'd like to use
permission() to hold a debugging check to make sure that
the mnt_want/drop_write() calls are actually being made.

So, to do this:
1. remove the IS_RDONLY() check from permission()
2. enforce that you must mnt_want_write() before
   even calling permission()
3. actually add the debugging check to permission()

We need to rearrange may_open() to do r/o checks
before calling permission().  Here's the patch.

Signed-off-by: Dave Hansen <haveblue@...ibm.com>
---

 lxc-dave/fs/namei.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff -puN fs/namei.c~rearrange-permission-and-ro-checks-in-may_open fs/namei.c
--- lxc/fs/namei.c~rearrange-permission-and-ro-checks-in-may_open	2007-09-20 12:16:09.000000000 -0700
+++ lxc-dave/fs/namei.c	2007-09-20 12:16:09.000000000 -0700
@@ -1579,10 +1579,6 @@ int may_open(struct nameidata *nd, int a
 	if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE))
 		return -EISDIR;

-	error = vfs_permission(nd, acc_mode);
-	if (error)
-		return error;
-
 	/*
 	 * FIFO's, sockets and device files are special: they don't
 	 * actually live on the filesystem itself, and as such you
@@ -1597,6 +1593,10 @@ int may_open(struct nameidata *nd, int a
 		flag &= ~O_TRUNC;
 	} else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
 		return -EROFS;
+
+	error = vfs_permission(nd, acc_mode);
+	if (error)
+		return error;
 	/*
 	 * An append-only file must be opened in append mode for writing.
 	 */
_
-
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