[PATCH 1/5] Use existing macros for distinguishing mandatory locks

[PATCH 1/5] Use existing macros for distinguishing mandatory locks

[Pavel Emelyanov]

The combination of S_ISGID bit set and S_IXGRP bit unset is 
used to mark the inode as "mandatory lockable" and there's a 
macro for this check called MANDATORY_LOCK(inode). However, 
fs/locks.c and some filesystems still perform the explicit 
i_mode checking. 

Switch the fs/locks.c to macro making the code shorter and 
more readable.

The __MANDATORY_LOCK() macro is to be used in places where
the IS_MANDLOCK() for superblock is already known to be true.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---

 fs/locks.c         |   14 ++++----------
 include/linux/fs.h |    4 ++--
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 291d40b..035ffda 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1488,8 +1488,8 @@ extern int locks_mandatory_area(int, str
  * Candidates for mandatory locking have the setgid bit set
  * but no group execute bit -  an otherwise meaningless combination.
  */
-#define MANDATORY_LOCK(inode) \
-	(IS_MANDLOCK(inode) && ((inode)->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+#define __MANDATORY_LOCK(ino) (((ino)->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+#define MANDATORY_LOCK(inode) (IS_MANDLOCK(inode) && __MANDATORY_LOCK(inode))
 
 static inline int locks_verify_locked(struct inode *inode)
 {
diff --git a/fs/locks.c b/fs/locks.c
index 0db1a14..f90fe6d 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1112,7 +1112,7 @@ int locks_mandatory_area(int read_write,
 			 * If we've been sleeping someone might have
 			 * changed the permissions behind our back.
 			 */
-			if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+			if (__MANDATORY_LOCK(inode))
 				continue;
 		}
 
@@ -1751,9 +1751,7 @@ int fcntl_setlk(unsigned int fd, struct 
 	/* Don't allow mandatory locks on files that may be memory mapped
 	 * and shared.
 	 */
-	if (IS_MANDLOCK(inode) &&
-	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
-	    mapping_writably_mapped(filp->f_mapping)) {
+	if (MANDATORY_LOCK(inode) && mapping_writably_mapped(filp->f_mapping)) {
 		error = -EAGAIN;
 		goto out;
 	}
@@ -1877,9 +1875,7 @@ int fcntl_setlk64(unsigned int fd, struc
 	/* Don't allow mandatory locks on files that may be memory mapped
 	 * and shared.
 	 */
-	if (IS_MANDLOCK(inode) &&
-	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
-	    mapping_writably_mapped(filp->f_mapping)) {
+	if (MANDATORY_LOCK(inode) && mapping_writably_mapped(filp->f_mapping)) {
 		error = -EAGAIN;
 		goto out;
 	}
@@ -2073,9 +2069,7 @@ static void lock_get_status(char* out, s
 		out += sprintf(out, "%6s %s ",
 			     (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
 			     (inode == NULL) ? "*NOINODE*" :
-			     (IS_MANDLOCK(inode) &&
-			      (inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
-			     "MANDATORY" : "ADVISORY ");
+			     MANDATORY_LOCK(inode) ? "MANDATORY" : "ADVISORY ");
 	} else if (IS_FLOCK(fl)) {
 		if (fl->fl_type & LOCK_MAND) {
 			out += sprintf(out, "FLOCK  MSNFS     ");

Re: [PATCH 1/5] Use existing macros for distinguishing mandatory locks

[Andrew Morton]

On Wed, 12 Sep 2007 15:17:58 +0400
Pavel Emelyanov <xemul@openvz.org> wrote:

> The combination of S_ISGID bit set and S_IXGRP bit unset is 
> used to mark the inode as "mandatory lockable" and there's a 
> macro for this check called MANDATORY_LOCK(inode). However, 
> fs/locks.c and some filesystems still perform the explicit 
> i_mode checking. 
> 
> Switch the fs/locks.c to macro making the code shorter and 
> more readable.
> 
> The __MANDATORY_LOCK() macro is to be used in places where
> the IS_MANDLOCK() for superblock is already known to be true.
> 

If we're going to churn this code then it would be better to switch from
ugly-upper-case-macro to nice-lower-case-C-function while we're doing it,
please.

> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 291d40b..035ffda 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1488,8 +1488,8 @@ extern int locks_mandatory_area(int, str
>   * Candidates for mandatory locking have the setgid bit set
>   * but no group execute bit -  an otherwise meaningless combination.
>   */
> -#define MANDATORY_LOCK(inode) \
> -	(IS_MANDLOCK(inode) && ((inode)->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
> +#define __MANDATORY_LOCK(ino) (((ino)->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
> +#define MANDATORY_LOCK(inode) (IS_MANDLOCK(inode) && __MANDATORY_LOCK(inode))

Especially as the macro is a buggy one which references its argument more
than once.