[PATCH 08/20] sysfs: Optimize just changing the sysfs file mode.

[Eric W. Biederman]

From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>

Don't allocate a struct iattr for the sysfs dentry if just
the mode changes because we have a field for that on the
sysfs_dirent, and we can trigger that case with sysfs_chmod_file.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxxxxxxxx>
---
 fs/sysfs/inode.c |   22 ++++++++++++++--------
 1 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 555f0ff..70ff2a2 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -60,12 +60,16 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
 		return error;
 
 	iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
+	if (iattr->ia_valid & ATTR_MODE) {
+		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
+			iattr->ia_mode &= ~S_ISGID;
+	}
 
 	error = inode_setattr(inode, iattr);
 	if (error)
 		return error;
 
-	if (!sd_iattr) {
+	if (!sd_iattr && (ia_valid & ~ATTR_MODE)) {
 		/* setting attributes for the first time, allocate now */
 		sd_iattr = kzalloc(sizeof(struct iattr), GFP_KERNEL);
 		if (!sd_iattr)
@@ -78,6 +82,13 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
 		sd->s_iattr = sd_iattr;
 	}
 
+	if (ia_valid & ATTR_MODE)
+		sd->s_mode = iattr->ia_mode;
+
+	/* If we don't need the extra attributes leave */
+	if (!sd_iattr)
+		return 0;
+
 	/* attributes were changed atleast once in past */
 
 	if (ia_valid & ATTR_UID)
@@ -93,13 +104,8 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
 	if (ia_valid & ATTR_CTIME)
 		sd_iattr->ia_ctime = timespec_trunc(iattr->ia_ctime,
 						inode->i_sb->s_time_gran);
-	if (ia_valid & ATTR_MODE) {
-		umode_t mode = iattr->ia_mode;
-
-		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
-			mode &= ~S_ISGID;
-		sd_iattr->ia_mode = sd->s_mode = mode;
-	}
+	if (ia_valid & ATTR_MODE)
+		sd_iattr->ia_mode = iattr->ia_mode;
 
 	return error;
 }
-- 
1.6.1.2.350.g88cc

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