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vfs: hoist degenerate path lookups out of the loop

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This commit is contained in:
Mateusz Guzik 2022-03-11 15:51:39 +00:00
parent 2587b74c61
commit 56244d3574
1 changed files with 77 additions and 33 deletions

110
sys/kern/vfs_lookup.c

@ -802,6 +802,57 @@ needs_exclusive_leaf(struct mount *mp, int flags)
_Static_assert(MAXNAMLEN == NAME_MAX,
"MAXNAMLEN and NAME_MAX have different values");
static int __noinline
vfs_lookup_degenerate(struct nameidata *ndp, struct vnode *dp, int wantparent)
{
struct componentname *cnp;
struct mount *mp;
int error;
cnp = &ndp->ni_cnd;
cnp->cn_flags |= ISLASTCN;
mp = atomic_load_ptr(&dp->v_mount);
if (needs_exclusive_leaf(mp, cnp->cn_flags)) {
cnp->cn_lkflags &= ~LK_SHARED;
cnp->cn_lkflags |= LK_EXCLUSIVE;
}
vn_lock(dp,
compute_cn_lkflags(mp, cnp->cn_lkflags | LK_RETRY,
cnp->cn_flags));
if (dp->v_type != VDIR) {
error = ENOTDIR;
goto bad;
}
if (cnp->cn_nameiop != LOOKUP) {
error = EISDIR;
goto bad;
}
if (wantparent) {
ndp->ni_dvp = dp;
VREF(dp);
}
ndp->ni_vp = dp;
if (cnp->cn_flags & AUDITVNODE1)
AUDIT_ARG_VNODE1(dp);
else if (cnp->cn_flags & AUDITVNODE2)
AUDIT_ARG_VNODE2(dp);
if (!(cnp->cn_flags & (LOCKPARENT | LOCKLEAF)))
VOP_UNLOCK(dp);
/* XXX This should probably move to the top of function. */
if (cnp->cn_flags & SAVESTART)
panic("lookup: SAVESTART");
return (0);
bad:
VOP_UNLOCK(dp);
return (error);
}
/*
* Search a pathname.
* This is a very central and rather complicated routine.
@ -886,13 +937,31 @@ vfs_lookup(struct nameidata *ndp)
rdonly = cnp->cn_flags & RDONLY;
cnp->cn_flags &= ~ISSYMLINK;
ndp->ni_dvp = NULL;
cnp->cn_lkflags = LK_SHARED;
dp = ndp->ni_startdir;
ndp->ni_startdir = NULLVP;
/*
* Leading slashes, if any, are supposed to be skipped by the caller.
*/
MPASS(cnp->cn_nameptr[0] != '/');
/*
* 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')) {
error = vfs_lookup_degenerate(ndp, dp, wantparent);
if (error == 0)
goto success_right_lock;
goto bad_unlocked;
}
/*
* We use shared locks until we hit the parent of the last cn then
* we adjust based on the requesting flags.
*/
cnp->cn_lkflags = LK_SHARED;
dp = ndp->ni_startdir;
ndp->ni_startdir = NULLVP;
vn_lock(dp,
compute_cn_lkflags(dp->v_mount, cnp->cn_lkflags | LK_RETRY,
cnp->cn_flags));
@ -980,37 +1049,10 @@ dirloop:
nameicap_tracker_add(ndp, dp);
/*
* Check for degenerate name (e.g. / or "")
* which is a way of talking about a directory,
* e.g. like "/." or ".".
* Make sure degenerate names don't get here, their handling was
* previously found in this spot.
*/
if (cnp->cn_nameptr[0] == '\0') {
if (dp->v_type != VDIR) {
error = ENOTDIR;
goto bad;
}
if (cnp->cn_nameiop != LOOKUP) {
error = EISDIR;
goto bad;
}
if (wantparent) {
ndp->ni_dvp = dp;
VREF(dp);
}
ndp->ni_vp = dp;
if (cnp->cn_flags & AUDITVNODE1)
AUDIT_ARG_VNODE1(dp);
else if (cnp->cn_flags & AUDITVNODE2)
AUDIT_ARG_VNODE2(dp);
if (!(cnp->cn_flags & (LOCKPARENT | LOCKLEAF)))
VOP_UNLOCK(dp);
/* XXX This should probably move to the top of function. */
if (cnp->cn_flags & SAVESTART)
panic("lookup: SAVESTART");
goto success;
}
MPASS(cnp->cn_nameptr[0] != '\0');
/*
* Handle "..": five special cases.
@ -1341,6 +1383,7 @@ success:
goto bad2;
}
}
success_right_lock:
if (ndp->ni_vp != NULL) {
if ((cnp->cn_flags & ISDOTDOT) == 0)
nameicap_tracker_add(ndp, ndp->ni_vp);
@ -1359,6 +1402,7 @@ bad2:
bad:
if (!dpunlocked)
vput(dp);
bad_unlocked:
ndp->ni_vp = NULL;
return (error);
bad_eexist: