Btrfs: try to only do one btrfs_search_slot in do_setxattr

I've been watching how many btrfs_search_slot()'s we do and I noticed that when
we create a file with selinux enabled we were doing 2 each time we initialize
the security context.  That's because we lookup the xattr first so we can delete
it if we're setting a new value to an existing xattr.  But in the create case we
don't have any xattrs, so it is completely useless to have the extra lookup.  So
re-arrange things so that we only lookup first if we specifically have
XATTR_REPLACE.  That way in the basic case we only do 1 search, and in the more
complicated case we do the normal 2 lookups.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 40 insertions, 26 deletions

diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index 5366fe452ab0..d733b9cfea34 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -102,43 +102,57 @@ static int do_setxattr(struct btrfs_trans_handle *trans,
         if (!path)
                 return -ENOMEM;
 
-        /* first lets see if we already have this xattr */
-        di = btrfs_lookup_xattr(trans, root, path, btrfs_ino(inode), name,
-                                strlen(name), -1);
-        if (IS_ERR(di)) {
-                ret = PTR_ERR(di);
-                goto out;
-        }
-
-        /* ok we already have this xattr, lets remove it */
-        if (di) {
-                /* if we want create only exit */
-                if (flags & XATTR_CREATE) {
-                        ret = -EEXIST;
+        if (flags & XATTR_REPLACE) {
+                di = btrfs_lookup_xattr(trans, root, path, btrfs_ino(inode), name,
+                                        name_len, -1);
+                if (IS_ERR(di)) {
+                        ret = PTR_ERR(di);
+                        goto out;
+                } else if (!di) {
+                        ret = -ENODATA;
                         goto out;
                 }
-
                 ret = btrfs_delete_one_dir_name(trans, root, path, di);
-                BUG_ON(ret);
+                if (ret)
+                        goto out;
                 btrfs_release_path(path);
+        }
 
-                /* if we don't have a value then we are removing the xattr */
-                if (!value)
+again:
+        ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
+                                      name, name_len, value, size);
+        if (ret == -EEXIST) {
+                if (flags & XATTR_CREATE)
                         goto out;
-        } else {
+                /*
+                 * We can't use the path we already have since we won't have the
+                 * proper locking for a delete, so release the path and
+                 * re-lookup to delete the thing.
+                 */
                 btrfs_release_path(path);
+                di = btrfs_lookup_xattr(trans, root, path, btrfs_ino(inode),
+                                        name, name_len, -1);
+                if (IS_ERR(di)) {
+                        ret = PTR_ERR(di);
+                        goto out;
+                } else if (!di) {
+                        /* Shouldn't happen but just in case... */
+                        btrfs_release_path(path);
+                        goto again;
+                }
 
-                if (flags & XATTR_REPLACE) {
-                        /* we couldn't find the attr to replace */
-                        ret = -ENODATA;
+                ret = btrfs_delete_one_dir_name(trans, root, path, di);
+                if (ret)
                         goto out;
+
+                /*
+                 * We have a value to set, so go back and try to insert it now.
+                 */
+                if (value) {
+                        btrfs_release_path(path);
+                        goto again;
                 }
         }
-
-        /* ok we have to create a completely new xattr */
-        ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
-                                      name, name_len, value, size);
-        BUG_ON(ret);
 out:
         btrfs_free_path(path);
         return ret;