linux-kernel - [RFC][PATCH v2 04/34] follow_automount() doesn't need the entire nameidata

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Message-Id: <20200223011626.4103706-4-viro@ZenIV.linux.org.uk>
Date:   Sun, 23 Feb 2020 01:15:56 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [RFC][PATCH v2 04/34] follow_automount() doesn't need the entire nameidata

From: Al Viro <viro@...iv.linux.org.uk>

Only the address of ->total_link_count and the flags.
And fix an off-by-one is ELOOP detection - make it
consistent with symlink following, where we check if
the pre-increment value has reached 40, rather than
check the post-increment one.

[kudos to Christian Brauner for spotted braino]

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/namei.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 39dd56f5171f..6721c5f7e9d5 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1208,7 +1208,7 @@ EXPORT_SYMBOL(follow_up);
  * - return -EISDIR to tell follow_managed() to stop and return the path we
  *   were called with.
  */
-static int follow_automount(struct path *path, struct nameidata *nd)
+static int follow_automount(struct path *path, int *count, unsigned lookup_flags)
 {
 	struct dentry *dentry = path->dentry;
 
@@ -1223,13 +1223,12 @@ static int follow_automount(struct path *path, struct nameidata *nd)
 	 * as being automount points.  These will need the attentions
 	 * of the daemon to instantiate them before they can be used.
 	 */
-	if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
+	if (!(lookup_flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
 			   LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
 	    dentry->d_inode)
 		return -EISDIR;
 
-	nd->total_link_count++;
-	if (nd->total_link_count >= 40)
+	if (count && (*count)++ >= MAXSYMLINKS)
 		return -ELOOP;
 
 	return finish_automount(dentry->d_op->d_automount(path), path);
@@ -1290,7 +1289,8 @@ static int follow_managed(struct path *path, struct nameidata *nd)
 
 		/* Handle an automount point */
 		if (flags & DCACHE_NEED_AUTOMOUNT) {
-			ret = follow_automount(path, nd);
+			ret = follow_automount(path, &nd->total_link_count,
+						nd->flags);
 			if (ret < 0)
 				break;
 			continue;
-- 
2.11.0