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cache: hoist trailing slash and degenerate path handling out of the loop

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Tested by:	pho
This commit is contained in:
Mateusz Guzik 2020-12-28 05:24:15 +01:00 committed by Mateusz Guzik
parent bb3a12f0e5
commit 67297766b5
1 changed files with 61 additions and 30 deletions
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91
sys/kern/vfs_cache.c
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@ -4685,6 +4685,51 @@ cache_fplookup_is_mp(struct cache_fpl *fpl)
* must take into account that in case off fallback the resulting
* nameidata state has to be compatible with the original.
*/
static int
cache_fplookup_preparse(struct cache_fpl *fpl)
{
struct nameidata *ndp;
struct componentname *cnp;
ndp = fpl->ndp;
cnp = fpl->cnp;
/*
* TODO
* Original comment:
* Check for degenerate name (e.g. / or "")
* which is a way of talking about a directory,
* e.g. like "/." or ".".
*/
if (__predict_false(cnp->cn_nameptr[0] == '\0')) {
return (cache_fpl_aborted(fpl));
}
/*
* By this point the shortest possible pathname is one character + nul
* terminator, hence 2.
*/
KASSERT(ndp->ni_pathlen >= 2, ("%s: ni_pathlen %zu\n", __func__,
ndp->ni_pathlen));
if (__predict_false(cnp->cn_nameptr[ndp->ni_pathlen - 2] == '/')) {
/*
* TODO
* Regular lookup performs the following:
* *ndp->ni_next = '\0';
* cnp->cn_flags |= TRAILINGSLASH;
*
* Which is problematic since it modifies data read
* from userspace. Then if fast path lookup was to
* abort we would have to either restore it or convey
* the flag. Since this is a corner case just ignore
* it for simplicity.
*/
return (cache_fpl_aborted(fpl));
}
return (0);
}
static int
cache_fplookup_parse(struct cache_fpl *fpl)
{
@ -4715,45 +4760,26 @@ cache_fplookup_parse(struct cache_fpl *fpl)
("%s: ni_pathlen underflow to %zd\n", __func__, ndp->ni_pathlen));
ndp->ni_next = cp;
#ifdef INVARIANTS
/*
* Replace multiple slashes by a single slash and trailing slashes
* by a null. This must be done before VOP_LOOKUP() because some
* fs's don't know about trailing slashes. Remember if there were
* trailing slashes to handle symlinks, existing non-directories
* and non-existing files that won't be directories specially later.
* Code below is only here to assure compatibility with regular lookup.
* It covers handling of trailing slashles and names like "/", both of
* which of can be taken care of upfront which lockless lookup does
* in cache_fplookup_preparse. Regular lookup performs these for each
* path component.
*/
while (*cp == '/' && (cp[1] == '/' || cp[1] == '\0')) {
cp++;
ndp->ni_pathlen--;
if (*cp == '\0') {
/*
* TODO
* Regular lookup performs the following:
* *ndp->ni_next = '\0';
* cnp->cn_flags |= TRAILINGSLASH;
*
* Which is problematic since it modifies data read
* from userspace. Then if fast path lookup was to
* abort we would have to either restore it or convey
* the flag. Since this is a corner case just ignore
* it for simplicity.
*/
return (cache_fpl_partial(fpl));
panic("%s: ran into TRAILINGSLASH handling from [%s]\n",
__func__, cnp->cn_pnbuf);
}
}
ndp->ni_next = cp;
/*
* Check for degenerate name (e.g. / or "")
* which is a way of talking about a directory,
* e.g. like "/." or ".".
*
* TODO
* Another corner case handled by the regular lookup
*/
if (__predict_false(cnp->cn_nameptr[0] == '\0')) {
return (cache_fpl_partial(fpl));
if (cnp->cn_nameptr[0] == '\0') {
panic("%s: ran into degenerate name from [%s]\n", __func__, cnp->cn_pnbuf);
}
#endif
return (0);
}
@ -4877,6 +4903,11 @@ cache_fplookup_impl(struct vnode *dvp, struct cache_fpl *fpl)
VNPASS(cache_fplookup_vnode_supported(fpl->dvp), fpl->dvp);
error = cache_fplookup_preparse(fpl);
if (__predict_false(error != 0)) {
goto out;
}
for (;;) {
error = cache_fplookup_parse(fpl);
if (__predict_false(error != 0)) {