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Subject[PATCH 70/79] namei: new calling conventions for walk_component()
Date
From: Al Viro <viro@zeniv.linux.org.uk>

instead of a single flag (!= 0 => we want to follow symlinks) pass
two bits - WALK_GET (want to follow symlinks) and WALK_PUT (put_link()
once we are done looking at the name). The latter matters only for
success exits - on failure the caller will discard everything anyway.

Suggestions for better variant are welcome; what this thing aims for
is making sure that pending put_link() is done *before* walk_component()
decides to pick a symlink up, rather than between picking it up and
acting upon it. See the next commit for payoff.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 30 ++++++++++++++++++++----------
1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 49ed4b5..5eb8b0c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1569,7 +1569,9 @@ static inline int should_follow_link(struct dentry *dentry, int follow)
return unlikely(d_is_symlink(dentry)) ? follow : 0;
}

-static int walk_component(struct nameidata *nd, int follow)
+enum {WALK_GET = 1, WALK_PUT = 2};
+
+static int walk_component(struct nameidata *nd, int flags)
{
struct path path;
struct inode *inode;
@@ -1579,8 +1581,12 @@ static int walk_component(struct nameidata *nd, int follow)
* to be able to know about the current root directory and
* parent relationships.
*/
- if (unlikely(nd->last_type != LAST_NORM))
- return handle_dots(nd, nd->last_type);
+ if (unlikely(nd->last_type != LAST_NORM)) {
+ err = handle_dots(nd, nd->last_type);
+ if (flags & WALK_PUT)
+ put_link(nd);
+ return err;
+ }
err = lookup_fast(nd, &path, &inode);
if (unlikely(err)) {
if (err < 0)
@@ -1596,7 +1602,9 @@ static int walk_component(struct nameidata *nd, int follow)
if (d_is_negative(path.dentry))
goto out_path_put;

- if (should_follow_link(path.dentry, follow)) {
+ if (flags & WALK_PUT)
+ put_link(nd);
+ if (should_follow_link(path.dentry, flags & WALK_GET)) {
if (nd->flags & LOOKUP_RCU) {
if (unlikely(nd->path.mnt != path.mnt ||
unlazy_walk(nd, path.dentry))) {
@@ -1808,10 +1816,9 @@ OK:
if (!name)
return 0;
/* last component of nested symlink */
- err = walk_component(nd, LOOKUP_FOLLOW);
- put_link(nd);
+ err = walk_component(nd, WALK_GET | WALK_PUT);
} else {
- err = walk_component(nd, LOOKUP_FOLLOW);
+ err = walk_component(nd, WALK_GET);
}
if (err < 0)
break;
@@ -2009,9 +2016,12 @@ static inline int lookup_last(struct nameidata *nd)
nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;

nd->flags &= ~LOOKUP_PARENT;
- err = walk_component(nd, nd->flags & LOOKUP_FOLLOW);
- if (nd->depth)
- put_link(nd);
+ err = walk_component(nd,
+ nd->flags & LOOKUP_FOLLOW
+ ? nd->depth
+ ? WALK_PUT | WALK_GET
+ : WALK_GET
+ : 0);
if (err < 0)
terminate_walk(nd);
return err;
--
2.1.4


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