[src/ad-namecache]: src/sys/kern - Adjust comments & assertions.

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/97f91f24bb4e
branches:  ad-namecache
changeset: 467259:97f91f24bb4e
user:      ad <ad%NetBSD.org@localhost>
date:      Sat Jan 18 15:42:02 2020 +0000

description:
- Adjust comments & assertions.
- Ditch memcmp().

diffstat:

 sys/kern/vfs_cache.c |  46 +++++++++++++++++++++++++++++++---------------
 1 files changed, 31 insertions(+), 15 deletions(-)

diffs (111 lines):

diff -r 65d3ef14b1bb -r 97f91f24bb4e sys/kern/vfs_cache.c
--- a/sys/kern/vfs_cache.c      Fri Jan 17 22:26:25 2020 +0000
+++ b/sys/kern/vfs_cache.c      Sat Jan 18 15:42:02 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_cache.c,v 1.126.2.6 2020/01/17 22:26:25 ad Exp $   */
+/*     $NetBSD: vfs_cache.c,v 1.126.2.7 2020/01/18 15:42:02 ad Exp $   */
 
 /*-
  * Copyright (c) 2008, 2019, 2020 The NetBSD Foundation, Inc.
@@ -148,7 +148,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.126.2.6 2020/01/17 22:26:25 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.126.2.7 2020/01/18 15:42:02 ad Exp $");
 
 #define __NAMECACHE_PRIVATE
 #ifdef _KERNEL_OPT
@@ -330,6 +330,22 @@
 }
 
 /*
+ * Like memcmp() but tuned for small strings of equal length.
+ */
+static inline int
+cache_namecmp(struct namecache *nc, const char *name, size_t namelen)
+{
+       size_t i;
+       int d;
+
+       KASSERT(nc->nc_nlen == namelen);
+       for (d = 0, i = 0; i < namelen; i++) {
+               d |= (nc->nc_name[i] ^ name[i]);
+       }
+       return d;
+}
+
+/*
  * Remove an entry from the cache.  The directory lock must be held, and if
  * "dir2node" is true, then we're locking in the conventional direction and
  * the list lock will be acquired when removing the entry from the vnode
@@ -378,11 +394,10 @@
 }
 
 /*
- * Find a single cache entry and return it locked.  The directory lock must
- * be held.
+ * Find a single cache entry and return it.  The nchnode lock must be held.
  *
  * Marked __noinline, and with everything unnecessary excluded, the compiler
- * (gcc 8.3.0 x86_64) does a great job on this.
+ * (gcc 8.3.0 x86_64) does a good job on this.
  */
 static struct namecache * __noinline
 cache_lookup_entry(struct nchnode *dnn, const char *name, size_t namelen,
@@ -394,12 +409,12 @@
        KASSERT(rw_lock_held(&dnn->nn_lock));
 
        /*
-        * Search the RB tree for the key.  This is one of the most
-        * performance sensitive code paths in the system, so here is an
-        * inlined version of rb_tree_find_node() tailored for exactly
-        * what's needed here (64-bit key and so on).  Elsewhere during
-        * entry/removal the generic functions are used as it doesn't
-        * matter so much there.
+        * Search the RB tree for the key.  File lookup is very performance
+        * sensitive, so here is an inlined lookup tailored for exactly
+        * what's needed here (64-bit key and so on) that is much faster
+        * than using rb_tree_find_node().  Elsewhere during entry/removal
+        * the generic functions are used as it doesn't matter so much
+        * there.
         */
        for (;;) {
                if (__predict_false(RB_SENTINEL_P(node))) {
@@ -415,8 +430,7 @@
        }
 
        /* Exclude collisions. */
-       KASSERT(nc->nc_nlen == namelen);
-       if (__predict_false(memcmp(nc->nc_name, name, namelen) != 0)) {
+       if (__predict_false(cache_namecmp(nc, name, namelen))) {
                return NULL;
        }
 
@@ -666,7 +680,7 @@
                        rw_exit(*plock);
                }
                *plock = &dnn->nn_lock;
-       } else {
+       } else if (*plock == NULL) {
                KASSERT(dvp->v_usecount > 0);
        }
 
@@ -674,6 +688,8 @@
         * First up check if the user is allowed to look up files in this
         * directory.
         */
+       KASSERT(dnn->nn_mode != VNOVAL && dnn->nn_uid != VNOVAL &&
+           dnn->nn_gid != VNOVAL);
        error = kauth_authorize_vnode(cred, KAUTH_ACCESS_ACTION(VEXEC,
            dvp->v_type, dnn->nn_mode & ALLPERMS), dvp, NULL,
            genfs_can_access(dvp->v_type, dnn->nn_mode & ALLPERMS,
@@ -857,7 +873,7 @@
        onc = rb_tree_find_node(&dnn->nn_tree, &nc->nc_key);
        if (onc) {
                KASSERT(onc->nc_nlen == nc->nc_nlen);
-               if (memcmp(onc->nc_name, nc->nc_name, nc->nc_nlen) != 0) {
+               if (cache_namecmp(onc, name, namelen)) {
                        COUNT(ncs_collisions);
                }
                cache_remove(onc, true);