kernfs: Add removed_size out param for simple_xattr_set

This helps set up size accounting in the next commit. Without this out
param, it's difficult to find out the removed xattr size without taking
a lock for longer and walking the xattr linked list twice.
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Acked-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

fs/kernfs/inode.c

@@ -303,7 +303,7 @@ int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
 	if (!attrs)
 		return -ENOMEM;
 
-	return simple_xattr_set(&attrs->xattrs, name, value, size, flags);
+	return simple_xattr_set(&attrs->xattrs, name, value, size, flags, NULL);
 }
 
 static int kernfs_vfs_xattr_get(const struct xattr_handler *handler,

fs/xattr.c

@@ -860,6 +860,7 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
  * @value: value of the xattr. If %NULL, will remove the attribute.
  * @size: size of the new xattr
  * @flags: %XATTR_{CREATE|REPLACE}
+ * @removed_size: returns size of the removed xattr, -1 if none removed
  *
  * %XATTR_CREATE is set, the xattr shouldn't exist already; otherwise fails
  * with -EEXIST.  If %XATTR_REPLACE is set, the xattr should exist;
@@ -868,7 +869,8 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
  * Returns 0 on success, -errno on failure.
  */
 int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
-		     const void *value, size_t size, int flags)
+		     const void *value, size_t size, int flags,
+		     ssize_t *removed_size)
 {
 	struct simple_xattr *xattr;
 	struct simple_xattr *new_xattr = NULL;
@@ -895,8 +897,12 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 				err = -EEXIST;
 			} else if (new_xattr) {
 				list_replace(&xattr->list, &new_xattr->list);
+				if (removed_size)
+					*removed_size = xattr->size;
 			} else {
 				list_del(&xattr->list);
+				if (removed_size)
+					*removed_size = xattr->size;
 			}
 			goto out;
 		}
@@ -908,6 +914,9 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 		list_add(&new_xattr->list, &xattrs->head);
 		xattr = NULL;
 	}
+
+	if (removed_size)
+		*removed_size = -1;
 out:
 	spin_unlock(&xattrs->lock);
 	if (xattr) {

include/linux/xattr.h

@@ -102,7 +102,8 @@ struct simple_xattr *simple_xattr_alloc(const void *value, size_t size);
 int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
 		     void *buffer, size_t size);
 int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
-		     const void *value, size_t size, int flags);
+		     const void *value, size_t size, int flags,
+		     ssize_t *removed_size);
 ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs, char *buffer,
 			  size_t size);
 void simple_xattr_list_add(struct simple_xattrs *xattrs,

mm/shmem.c

@@ -3243,7 +3243,7 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 	struct shmem_inode_info *info = SHMEM_I(inode);
 
 	name = xattr_full_name(handler, name);
-	return simple_xattr_set(&info->xattrs, name, value, size, flags);
+	return simple_xattr_set(&info->xattrs, name, value, size, flags, NULL);
 }
 
 static const struct xattr_handler shmem_security_xattr_handler = {