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    Subject[PATCH 16/24] link_path_walk: kill the recursion
    Date
    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


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