[PATCH 08/24] namei.c: separate the parts of follow_link() that find the link body

Al Viro
2015-04-20T18:19:18Z

From: Al Viro <viro@zeniv.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@zeniv.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