[PATCH 16/24] link_path_walk: kill the recursion

Al Viro
2015-04-20T18:14:47Z

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

absolutely straightforward now - the only variables we need to preserve
across the recursive call are name, link and cookie, and recursion depth
is limited (and can is equal to nd->depth). So arrange an array of
triples to hold instances of those and be done with that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 40 +++++++++++++++++++++++++++++-----------
1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 6d79e00..4b98f4b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1767,9 +1767,15 @@ static inline u64 hash_name(const char *name)
*/
static int link_path_walk(const char *name, struct nameidata *nd)
{
+ struct saved {
+ struct path link;
+ void *cookie;
+ const char *name;
+ } stack[MAX_NESTED_LINKS], *last = stack + nd->depth - 1;
struct path next;
int err;
-
+
+start:
while (*name=='/')
name++;
if (!*name)
@@ -1833,8 +1839,6 @@ Walked:
goto Err;

if (err) {
- struct path link;
- void *cookie;
char *s;

if (unlikely(nd->link_count >= MAX_NESTED_LINKS)) {
@@ -1847,22 +1851,25 @@ Walked:

nd->depth++;
nd->link_count++;
+ last++;

- link = next;
- s = get_link(&link, nd, &cookie);
+ last->link = next;
+ s = get_link(&last->link, nd, &last->cookie);

if (unlikely(IS_ERR(s))) {
err = PTR_ERR(s);
nd->link_count--;
nd->depth--;
+ last--;
goto Err;
}
err = 0;
if (unlikely(!s)) {
/* jumped */
- put_link(nd, &link, cookie);
+ put_link(nd, &last->link, last->cookie);
nd->link_count--;
nd->depth--;
+ last--;
} else {
if (*s == '/') {
if (!nd->root.mnt)
@@ -1873,17 +1880,24 @@ Walked:
nd->flags |= LOOKUP_JUMPED;
}
nd->inode = nd->path.dentry->d_inode;
- err = link_path_walk(s, nd);
+ last->name = name;
+ name = s;
+ goto start;
+
+back:
+ name = last->name;
if (unlikely(err)) {
- put_link(nd, &link, cookie);
+ put_link(nd, &last->link, last->cookie);
nd->link_count--;
nd->depth--;
+ last--;
goto Err;
} else {
err = walk_component(nd, &next, LOOKUP_FOLLOW);
- put_link(nd, &link, cookie);
+ put_link(nd, &last->link, last->cookie);
nd->link_count--;
nd->depth--;
+ last--;
goto Walked;
}
}
@@ -1895,9 +1909,13 @@ Walked:
}
terminate_walk(nd);
Err:
- return err;
+ if (likely(!nd->depth))
+ return err;
+ goto back;
OK:
- return 0;
+ if (likely(!nd->depth))
+ return 0;
+ goto back;
}

static int path_init(int dfd, const struct filename *name, unsigned int flags,
--
2.1.4