VFS: Differentiate mount flags (MS_*) from internal superblock flags

Differentiate the MS_* flags passed to mount(2) from the internal flags set
in the super_block's s_flags.  s_flags are now called SB_*, with the names
and the values for the moment mirroring the MS_* flags that they're
equivalent to.

In this patch, just the headers are altered and some kernel code where
blind automated conversion isn't necessarily correct.

Note that this shows up some interesting issues:

 (1) Some MS_* flags get translated to MNT_* flags (such as MS_NODEV ->
     MNT_NODEV) without passing this on to the filesystem, but some
     filesystems set such flags anyway.

 (2) The ->remount_fs() methods of some filesystems adjust the *flags
     argument by setting MS_* flags in it, such as MS_NOATIME - but these
     flags are then scrubbed by do_remount_sb() (only the occupants of
     MS_RMT_MASK are permitted: MS_RDONLY, MS_SYNCHRONOUS, MS_MANDLOCK,
     MS_I_VERSION and MS_LAZYTIME)

I'm not sure what's the best way to solve all these cases.

Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 36 insertions, 9 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6ae137c1bdf6..3d6ee0c0ebb0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1270,6 +1270,33 @@ extern int send_sigurg(struct fown_struct *fown);
 struct mm_struct;
 
 /*
+ * sb->s_flags.  Note that these mirror the equivalent MS_* flags where
+ * represented in both.
+ */
+#define SB_RDONLY        1      /* Mount read-only */
+#define SB_NOSUID        2      /* Ignore suid and sgid bits */
+#define SB_NODEV         4      /* Disallow access to device special files */
+#define SB_NOEXEC        8      /* Disallow program execution */
+#define SB_SYNCHRONOUS  16      /* Writes are synced at once */
+#define SB_MANDLOCK     64      /* Allow mandatory locks on an FS */
+#define SB_DIRSYNC      128     /* Directory modifications are synchronous */
+#define SB_NOATIME      1024    /* Do not update access times. */
+#define SB_NODIRATIME   2048    /* Do not update directory access times */
+#define SB_SILENT       32768
+#define SB_POSIXACL     (1<<16) /* VFS does not apply the umask */
+#define SB_KERNMOUNT    (1<<22) /* this is a kern_mount call */
+#define SB_I_VERSION    (1<<23) /* Update inode I_version field */
+#define SB_LAZYTIME     (1<<25) /* Update the on-disk [acm]times lazily */
+
+/* These sb flags are internal to the kernel */
+#define SB_SUBMOUNT     (1<<26)
+#define SB_NOREMOTELOCK (1<<27)
+#define SB_NOSEC        (1<<28)
+#define SB_BORN         (1<<29)
+#define SB_ACTIVE       (1<<30)
+#define SB_NOUSER       (1<<31)
+
+/*
  *      Umount options
  */
 
@@ -1835,7 +1862,7 @@ struct super_operations {
  * possible to override it selectively if you really wanted to with some
  * ioctl() that is not currently implemented.
  *
- * Exception: MS_RDONLY is always applied to the entire file system.
+ * Exception: SB_RDONLY is always applied to the entire file system.
  *
  * Unfortunately, it is possible to change a filesystems flags with it mounted
  * with files in use.  This means that all of the inodes will not have their
@@ -1846,18 +1873,18 @@ struct super_operations {
 
 static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags & MS_RDONLY; }
 #define IS_RDONLY(inode)        sb_rdonly((inode)->i_sb)
-#define IS_SYNC(inode)          (__IS_FLG(inode, MS_SYNCHRONOUS) || \
+#define IS_SYNC(inode)          (__IS_FLG(inode, SB_SYNCHRONOUS) || \
                                         ((inode)->i_flags & S_SYNC))
-#define IS_DIRSYNC(inode)       (__IS_FLG(inode, MS_SYNCHRONOUS|MS_DIRSYNC) || \
+#define IS_DIRSYNC(inode)       (__IS_FLG(inode, SB_SYNCHRONOUS|SB_DIRSYNC) || \
                                         ((inode)->i_flags & (S_SYNC|S_DIRSYNC)))
-#define IS_MANDLOCK(inode)      __IS_FLG(inode, MS_MANDLOCK)
-#define IS_NOATIME(inode)       __IS_FLG(inode, MS_RDONLY|MS_NOATIME)
-#define IS_I_VERSION(inode)     __IS_FLG(inode, MS_I_VERSION)
+#define IS_MANDLOCK(inode)      __IS_FLG(inode, SB_MANDLOCK)
+#define IS_NOATIME(inode)       __IS_FLG(inode, SB_RDONLY|SB_NOATIME)
+#define IS_I_VERSION(inode)     __IS_FLG(inode, SB_I_VERSION)
 
 #define IS_NOQUOTA(inode)       ((inode)->i_flags & S_NOQUOTA)
 #define IS_APPEND(inode)        ((inode)->i_flags & S_APPEND)
 #define IS_IMMUTABLE(inode)     ((inode)->i_flags & S_IMMUTABLE)
-#define IS_POSIXACL(inode)      __IS_FLG(inode, MS_POSIXACL)
+#define IS_POSIXACL(inode)      __IS_FLG(inode, SB_POSIXACL)
 
 #define IS_DEADDIR(inode)       ((inode)->i_flags & S_DEAD)
 #define IS_NOCMTIME(inode)      ((inode)->i_flags & S_NOCMTIME)
@@ -2178,7 +2205,7 @@ static inline int __mandatory_lock(struct inode *ino)
 }
 
 /*
- * ... and these candidates should be on MS_MANDLOCK mounted fs,
+ * ... and these candidates should be on SB_MANDLOCK mounted fs,
  * otherwise these will be advisory locks
  */
 
@@ -3274,7 +3301,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
 
 static inline void inode_has_no_xattr(struct inode *inode)
 {
-        if (!is_sxid(inode->i_mode) && (inode->i_sb->s_flags & MS_NOSEC))
+        if (!is_sxid(inode->i_mode) && (inode->i_sb->s_flags & SB_NOSEC))
                 inode->i_flags |= S_NOSEC;
 }