linux-kernel - [PATCH 08/24] namei.c: separate the parts of follow

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Message-Id: <1429553588-24764-8-git-send-email-viro@ZenIV.linux.org.uk>
Date:	Mon, 20 Apr 2015 19:12:52 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Neil Brown <neilb@...e.de>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH 08/24] namei.c: separate the parts of follow_link() that find the link body

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

Calling conventions for ->follow_link() are rather unfortunate.  It
would be better to have it return ERR_PTR(error) on error, NULL on
jumps and link body for normal symlinks.  What we currently return
(opaque pointer used by ->put_link() once we are done) should've
been given to analogue (and replacement) of nd_set_link().

For now let's just split a piece of fs/namei.c:follow_link() that
does obtaining the link body into a separate function.  When we
get around to changing ->follow_link() API, the changes will be
contained in that sucker.  follow_link() itself converted to
calling get_link() and then doing the body traversal (if any).

The next step will expand follow_link() call in link_path_walk()
and this helps to keep the size down...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/namei.c | 79 +++++++++++++++++++++++++++++++++++---------------------------
 1 file changed, 45 insertions(+), 34 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index a1f6271..e07bf5c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -871,21 +871,23 @@ static int may_linkat(struct path *link)
 	return -EPERM;
 }
 
-static __always_inline int
-follow_link(struct path *link, struct nameidata *nd, void **p)
+static __always_inline char *
+get_link(struct path *link, struct nameidata *nd, void **p)
 {
 	struct dentry *dentry = link->dentry;
+	struct inode *inode = dentry->d_inode;
+	void *cookie;
 	int error;
-	char *s;
+	char *res;
 
 	BUG_ON(nd->flags & LOOKUP_RCU);
 
 	if (link->mnt == nd->path.mnt)
 		mntget(link->mnt);
 
-	error = -ELOOP;
+	res = ERR_PTR(-ELOOP);
 	if (unlikely(nd->total_link_count >= 40))
-		goto out_put_nd_path;
+		goto out;
 
 	cond_resched();
 	nd->total_link_count++;
@@ -893,44 +895,53 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 	touch_atime(link);
 	nd_set_link(NULL);
 
-	error = security_inode_follow_link(link->dentry);
+	error = security_inode_follow_link(dentry);
+	res = ERR_PTR(error);
 	if (error)
-		goto out_put_nd_path;
+		goto out;
 
 	nd->last_type = LAST_BIND;
-	*p = dentry->d_inode->i_op->follow_link(dentry);
-	error = PTR_ERR(*p);
-	if (IS_ERR(*p))
-		goto out_put_nd_path;
+	res = cookie = inode->i_op->follow_link(dentry);
+	if (IS_ERR(cookie))
+		goto out;
 
-	error = 0;
-	s = nd_get_link(nd);
-	if (s) {
-		if (unlikely(IS_ERR(s))) {
-			path_put(&nd->path);
-			put_link(nd, link, *p);
-			return PTR_ERR(s);
-		}
-		if (*s == '/') {
-			if (!nd->root.mnt)
-				set_root(nd);
-			path_put(&nd->path);
-			nd->path = nd->root;
-			path_get(&nd->root);
-			nd->flags |= LOOKUP_JUMPED;
-		}
-		nd->inode = nd->path.dentry->d_inode;
-		error = link_path_walk(s, nd);
-		if (unlikely(error))
-			put_link(nd, link, *p);
+	res = nd_get_link(nd);
+	if (!IS_ERR(res)) {
+		*p = cookie;
+		return res;
 	}
 
-	return error;
-
-out_put_nd_path:
+	if (inode->i_op->put_link)
+		inode->i_op->put_link(dentry, res, cookie);
+out:
 	*p = NULL;
 	path_put(&nd->path);
 	path_put(link);
+	return res;
+}
+
+static __always_inline int
+follow_link(struct path *link, struct nameidata *nd, void **p)
+{
+	char *s = get_link(link, nd, p);
+	int error;
+
+	if (unlikely(IS_ERR(s)))
+		return PTR_ERR(s);
+	if (unlikely(!s))
+		return 0;
+	if (*s == '/') {
+		if (!nd->root.mnt)
+			set_root(nd);
+		path_put(&nd->path);
+		nd->path = nd->root;
+		path_get(&nd->root);
+		nd->flags |= LOOKUP_JUMPED;
+	}
+	nd->inode = nd->path.dentry->d_inode;
+	error = link_path_walk(s, nd);
+	if (unlikely(error))
+		put_link(nd, link, *p);
 	return error;
 }
 
-- 
2.1.4

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