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namei: new calling conventions for walk_component() 

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>
This commit is contained in:
Al Viro 2015-05-04 17:47:11 -04:00
parent 8620c238ed
commit 4693a547cd
1 changed files with 20 additions and 10 deletions
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30
fs/namei.c
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@ -1577,7 +1577,9 @@ 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;
@ -1587,8 +1589,12 @@ 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)
@ -1604,7 +1610,9 @@ static int walk_component(struct nameidata *nd, int follow)
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))) {
@ -1816,10 +1824,9 @@ static int link_path_walk(const char *name, struct nameidata *nd)
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;
@ -2017,9 +2024,12 @@ 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;