[PATCH] Introduce FMODE_EXEC file flag

Introduce FMODE_EXEC file flag, to indicate that file is being opened for
execution.  This is useful for distributed filesystems to maintain
consistent behavior for returning ETXTBUSY when opening for write and
execution happens on different nodes.

akpm:

  Needed by Lustre at present.  I assume their objective to to work towards
  being able to install Lustre on an unmodified distro kernel, which seems
  sane.  It should have zero runtime cost.

  Trond and Chuck indicate that NFS4 can probably use this too, for the same
  thing.

  Steven says it's also on the GFS todo list.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Chuck Lever <cel@citi.umich.edu>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/exec.c

@@ -127,7 +127,7 @@ asmlinkage long sys_uselib(const char __user * library)
 	struct nameidata nd;
 	int error;
 
-	error = __user_path_lookup_open(library, LOOKUP_FOLLOW, &nd, FMODE_READ);
+	error = __user_path_lookup_open(library, LOOKUP_FOLLOW, &nd, FMODE_READ|FMODE_EXEC);
 	if (error)
 		goto out;
 
@@ -477,7 +477,7 @@ struct file *open_exec(const char *name)
 	int err;
 	struct file *file;
 
-	err = path_lookup_open(AT_FDCWD, name, LOOKUP_FOLLOW, &nd, FMODE_READ);
+	err = path_lookup_open(AT_FDCWD, name, LOOKUP_FOLLOW, &nd, FMODE_READ|FMODE_EXEC);
 	file = ERR_PTR(err);
 
 	if (!err) {

include/linux/fs.h

@@ -65,6 +65,11 @@ extern int dir_notify_enable;
 #define FMODE_PREAD	8
 #define FMODE_PWRITE	FMODE_PREAD	/* These go hand in hand */
 
+/* File is being opened for execution. Primary users of this flag are
+   distributed filesystems that can use it to achieve correct ETXTBUSY
+   behavior for cross-node execution/opening_for_writing of files */
+#define FMODE_EXEC	16
+
 #define RW_MASK		1
 #define RWA_MASK	2
 #define READ 0