vfs: separate FMODE_PREAD/FMODE_PWRITE into separate flags

Separate FMODE_PREAD and FMODE_PWRITE into separate flags to reflect the
reality that the read and write paths may have independent restrictions.

A git grep verifies that these flags are always cleared together so this
new behavior will only apply to interfaces that change to clear flags
individually.

This is required for "seq_file: properly cope with pread", a post-2.6.25
regression fix.

[akpm@linux-foundation.org: add comment]
Signed-off-by: Paul Turner <pjt@google.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc:  Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@kernel.org>		[2.6.25.x, 2.6.26.x, 2.6.27.x, 2.6.28.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fs.h

@@ -54,24 +54,30 @@ struct inodes_stat_t {
 #define MAY_ACCESS 16
 #define MAY_OPEN 32
 
+/*
+ * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
+ * to O_WRONLY and O_RDWR via the strange trick in __dentry_open()
+ */
+
 /* file is open for reading */
 #define FMODE_READ		((__force fmode_t)1)
 /* file is open for writing */
 #define FMODE_WRITE		((__force fmode_t)2)
 /* file is seekable */
 #define FMODE_LSEEK		((__force fmode_t)4)
-/* file can be accessed using pread/pwrite */
+/* file can be accessed using pread */
 #define FMODE_PREAD		((__force fmode_t)8)
-#define FMODE_PWRITE		FMODE_PREAD	/* These go hand in hand */
+/* file can be accessed using pwrite */
+#define FMODE_PWRITE		((__force fmode_t)16)
 /* File is opened for execution with sys_execve / sys_uselib */
-#define FMODE_EXEC		((__force fmode_t)16)
+#define FMODE_EXEC		((__force fmode_t)32)
 /* File is opened with O_NDELAY (only set for block devices) */
-#define FMODE_NDELAY		((__force fmode_t)32)
+#define FMODE_NDELAY		((__force fmode_t)64)
 /* File is opened with O_EXCL (only set for block devices) */
-#define FMODE_EXCL		((__force fmode_t)64)
+#define FMODE_EXCL		((__force fmode_t)128)
 /* File is opened using open(.., 3, ..) and is writeable only for ioctls
    (specialy hack for floppy.c) */
-#define FMODE_WRITE_IOCTL	((__force fmode_t)128)
+#define FMODE_WRITE_IOCTL	((__force fmode_t)256)
 
 /*
  * Don't update ctime and mtime.