switch atomic_open() and lookup_open() to returning 0 in all success cases

caller can tell "opened" from "open it yourself" by looking at ->f_mode.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -3027,9 +3027,9 @@ static int may_o_create(const struct path *dir, struct dentry *dentry, umode_t m
  * Returns 0 if successful.  The file will have been created and attached to
  * @file by the filesystem calling finish_open().
  *
- * Returns 1 if the file was looked up only or didn't need creating.  The
- * caller will need to perform the open themselves.  @path will have been
- * updated to point to the new dentry.  This may be negative.
+ * If the file was looked up only or didn't need creating, FMODE_OPENED won't
+ * be set.  The caller will need to perform the open themselves.  @path will
+ * have been updated to point to the new dentry.  This may be negative.
  *
  * Returns an error code otherwise.
  */
@@ -3082,7 +3082,7 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
 			} else {
 				path->dentry = dentry;
 				path->mnt = nd->path.mnt;
-				return 1;
+				return 0;
 			}
 		}
 	}
@@ -3093,17 +3093,17 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
 /*
  * Look up and maybe create and open the last component.
  *
- * Must be called with i_mutex held on parent.
- *
- * Returns 0 if the file was successfully atomically created (if necessary) and
- * opened.  In this case the file will be returned attached to @file.
+ * Must be called with parent locked (exclusive in O_CREAT case).
  *
- * Returns 1 if the file was not completely opened at this time, though lookups
- * and creations will have been performed and the dentry returned in @path will
- * be positive upon return if O_CREAT was specified.  If O_CREAT wasn't
- * specified then a negative dentry may be returned.
+ * Returns 0 on success, that is, if
+ *  the file was successfully atomically created (if necessary) and opened, or
+ *  the file was not completely opened at this time, though lookups and
+ *  creations were performed.
+ * These case are distinguished by presence of FMODE_OPENED on file->f_mode.
+ * In the latter case dentry returned in @path might be negative if O_CREAT
+ * hadn't been specified.
  *
- * An error code is returned otherwise.
+ * An error code is returned on failure.
  */
 static int lookup_open(struct nameidata *nd, struct path *path,
 			struct file *file,
@@ -3225,7 +3225,7 @@ no_open:
 out_no_open:
 	path->dentry = dentry;
 	path->mnt = nd->path.mnt;
-	return 1;
+	return 0;
 
 out_dput:
 	dput(dentry);
@@ -3308,10 +3308,10 @@ static int do_last(struct nameidata *nd,
 	else
 		inode_unlock_shared(dir->d_inode);
 
-	if (error <= 0) {
-		if (error)
-			goto out;
+	if (error)
+		goto out;
 
+	if (file->f_mode & FMODE_OPENED) {
 		if ((file->f_mode & FMODE_CREATED) ||
 		    !S_ISREG(file_inode(file)->i_mode))
 			will_truncate = false;