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Subject[PATCH 52/79] link_path_walk: nd->depth massage, part 1
Date
From: Al Viro <viro@zeniv.linux.org.uk>

nd->stack[0] is unused until the handling of trailing symlinks and
we want to get rid of that. Having fucked that transformation up
several times, I went for bloody pedantic series of provably equivalent
transformations. Sorry.

Step 1: keep nd->depth higher by one in link_path_walk() - increment upon
entry, decrement on exits, adjust the arithmetics inside and surround the
calls of functions that care about nd->depth value (nd_alloc_stack(),
get_link(), put_link()) with decrement/increment pairs.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 078db1d..da23835 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1755,6 +1755,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
if (!*name)
return 0;

+ nd->depth++;
/* At this point we know we have a real path component. */
for(;;) {
u64 hash_len;
@@ -1815,15 +1816,18 @@ Walked:
if (err) {
const char *s;

+ nd->depth--;
err = nd_alloc_stack(nd);
+ nd->depth++;
if (unlikely(err)) {
path_to_nameidata(&nd->link, nd);
break;
}

nd->depth++;
-
+ nd->depth--;
s = get_link(nd);
+ nd->depth++;

if (unlikely(IS_ERR(s))) {
err = PTR_ERR(s);
@@ -1833,7 +1837,9 @@ Walked:
err = 0;
if (unlikely(!s)) {
/* jumped */
+ nd->depth--;
put_link(nd);
+ nd->depth++;
nd->depth--;
} else {
if (*s == '/') {
@@ -1847,7 +1853,7 @@ Walked:
;
}
nd->inode = nd->path.dentry->d_inode;
- nd->stack[nd->depth].name = name;
+ nd->stack[nd->depth - 1].name = name;
if (!*s)
goto OK;
name = s;
@@ -1861,19 +1867,25 @@ Walked:
}
terminate_walk(nd);
Err:
- while (unlikely(nd->depth)) {
+ while (unlikely(nd->depth > 1)) {
+ nd->depth--;
put_link(nd);
+ nd->depth++;
nd->depth--;
}
+ nd->depth--;
return err;
OK:
- if (unlikely(nd->depth)) {
- name = nd->stack[nd->depth].name;
+ if (unlikely(nd->depth > 1)) {
+ name = nd->stack[nd->depth - 1].name;
err = walk_component(nd, LOOKUP_FOLLOW);
+ nd->depth--;
put_link(nd);
+ nd->depth++;
nd->depth--;
goto Walked;
}
+ nd->depth--;
return 0;
}

--
2.1.4


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