Optimize symlink/directory detection

This is the base for making symlink detection in the middle fo a pathname
saner and (much) more efficient.

Under various loads, we want to verify that the full path leading up to a
filename is a real directory tree, and that when we successfully do an
'lstat()' on a filename, we don't get a false positive due to a symlink in
the middle of the path that git should have seen as a symlink, not as a
normal path component.

The 'has_symlink_leading_path()' function already did this, and cached
a single level of symlink information, but didn't cache the _lack_ of a
symlink, so the normal behaviour was actually the wrong way around, and we
ended up doing an 'lstat()' on each path component to check that it was a
real directory.

This caches the last detected full directory and symlink entries, and
speeds up especially deep directory structures a lot by avoiding to
lstat() all the directories leading up to each entry in the index.

[ This can - and should - probably be extended upon so that we eventually
  never do a bare 'lstat()' on any path entries at *all* when checking the
  index, but always check the full path carefully. Right now we do not
  generally check the whole path for all our normal quick index
  revalidation.

  We should also make sure that we're careful about all the invalidation,
  ie when we remove a link and replace it by a directory we should
  invalidate the symlink cache if it matches (and vice versa for the
  directory cache).

  But regardless, the basic function needs to be sane to do that. The old
  'has_symlink_leading_path()' was not capable enough - or indeed the code
  readable enough - to really do that sanely. So I'm pushing this as not
  just an optimization, but as a base for further work. ]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-apply.c b/builtin-apply.c
index caa3f2aa0ca147091d28013c3d2c11346e350675..1103625a4a923d92ca8d335d1a872236630541e5 100644 (file)
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -2247,7 +2247,7 @@ static int check_to_create_blob(const char *new_name, int ok_if_exists)
                 * In such a case, path "new_name" does not exist as
                 * far as git is concerned.
                 */
-               if (has_symlink_leading_path(new_name, NULL))
+               if (has_symlink_leading_path(strlen(new_name), new_name))
                        return 0;
 
                return error("%s: already exists in working directory", new_name);

diff --git a/cache.h b/cache.h
index 4803b032ec1d52f3253060c0bdbe09a4796f346e..0d9d9e25770cd18cf83b810dc29ec10163aa1620 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -598,7 +598,7 @@ struct checkout {
 };
 
 extern int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *topath);
-extern int has_symlink_leading_path(const char *name, char *last_symlink);
+extern int has_symlink_leading_path(int len, const char *name);
 
 extern struct alternate_object_database {
        struct alternate_object_database *next;

diff --git a/diff-lib.c b/diff-lib.c
index c5894c7c5aa166370f407ace804dc1a857d04fe4..fe2ccec7e6b3230715cbdf04591d1c0efb6a6389 100644 (file)
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -347,14 +347,14 @@ int run_diff_files_cmd(struct rev_info *revs, int argc, const char **argv)
  * exists for ce that is a submodule -- it is a submodule that is not
  * checked out).  Return negative for an error.
  */
-static int check_removed(const struct cache_entry *ce, struct stat *st, char *symcache)
+static int check_removed(const struct cache_entry *ce, struct stat *st)
 {
        if (lstat(ce->name, st) < 0) {
                if (errno != ENOENT && errno != ENOTDIR)
                        return -1;
                return 1;
        }
-       if (has_symlink_leading_path(ce->name, symcache))
+       if (has_symlink_leading_path(ce_namelen(ce), ce->name))
                return 1;
        if (S_ISDIR(st->st_mode)) {
                unsigned char sub[20];
@@ -421,7 +421,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
                        memset(&(dpath->parent[0]), 0,
                               sizeof(struct combine_diff_parent)*5);
 
-                       changed = check_removed(ce, &st, symcache);
+                       changed = check_removed(ce, &st);
                        if (!changed)
                                dpath->mode = ce_mode_from_stat(ce, st.st_mode);
                        else {
@@ -485,7 +485,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
                if (ce_uptodate(ce))
                        continue;
 
-               changed = check_removed(ce, &st, symcache);
+               changed = check_removed(ce, &st);
                if (changed) {
                        if (changed < 0) {
                                perror(ce->name);
@@ -546,7 +546,7 @@ static int get_stat_data(struct cache_entry *ce,
        if (!cached) {
                int changed;
                struct stat st;
-               changed = check_removed(ce, &st, cbdata->symcache);
+               changed = check_removed(ce, &st);
                if (changed < 0)
                        return -1;
                else if (changed) {

diff --git a/symlinks.c b/symlinks.c
index be9ace6c04ce1fe7d53d85f30adab2218ec1ec65..5a5e781a15d7d9cb60797958433eca896b31ec85 100644 (file)
--- a/symlinks.c
+++ b/symlinks.c
@@ -1,48 +1,64 @@
 #include "cache.h"
 
-int has_symlink_leading_path(const char *name, char *last_symlink)
-{
+struct pathname {
+       int len;
        char path[PATH_MAX];
-       const char *sp, *ep;
-       char *dp;
-
-       sp = name;
-       dp = path;
-
-       if (last_symlink && *last_symlink) {
-               size_t last_len = strlen(last_symlink);
-               size_t len = strlen(name);
-               if (last_len < len &&
-                   !strncmp(name, last_symlink, last_len) &&
-                   name[last_len] == '/')
-                       return 1;
-               *last_symlink = '\0';
+};
+
+/* Return matching pathname prefix length, or zero if not matching */
+static inline int match_pathname(int len, const char *name, struct pathname *match)
+{
+       int match_len = match->len;
+       return (len > match_len &&
+               name[match_len] == '/' &&
+               !memcmp(name, match->path, match_len)) ? match_len : 0;
+}
+
+static inline void set_pathname(int len, const char *name, struct pathname *match)
+{
+       if (len < PATH_MAX) {
+               match->len = len;
+               memcpy(match->path, name, len);
+               match->path[len] = 0;
        }
+}
+
+int has_symlink_leading_path(int len, const char *name)
+{
+       static struct pathname link, nonlink;
+       char path[PATH_MAX];
+       struct stat st;
+       char *sp;
+       int known_dir;
 
-       while (1) {
-               size_t len;
-               struct stat st;
+       /*
+        * See if the last known symlink cache matches.
+        */
+       if (match_pathname(len, name, &link))
+               return 1;
 
-               ep = strchr(sp, '/');
-               if (!ep)
-                       break;
-               len = ep - sp;
-               if (PATH_MAX <= dp + len - path + 2)
-                       return 0; /* new name is longer than that??? */
-               memcpy(dp, sp, len);
-               dp[len] = 0;
+       /*
+        * Get rid of the last known directory part
+        */
+       known_dir = match_pathname(len, name, &nonlink);
+
+       while ((sp = strchr(name + known_dir + 1, '/')) != NULL) {
+               int thislen = sp - name ;
+               memcpy(path, name, thislen);
+               path[thislen] = 0;
 
                if (lstat(path, &st))
                        return 0;
+               if (S_ISDIR(st.st_mode)) {
+                       set_pathname(thislen, path, &nonlink);
+                       known_dir = thislen;
+                       continue;
+               }
                if (S_ISLNK(st.st_mode)) {
-                       if (last_symlink)
-                               strcpy(last_symlink, path);
+                       set_pathname(thislen, path, &link);
                        return 1;
                }
-
-               dp[len++] = '/';
-               dp = dp + len;
-               sp = ep + 1;
+               break;
        }
        return 0;
 }

diff --git a/unpack-trees.c b/unpack-trees.c
index feae846226237fce9b4ff4a4810a9961637a4ca5..1ab28fda45be940b300b504ae029f3fba2c28fa9 100644 (file)
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -26,11 +26,12 @@ static void add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
  * directories, in case this unlink is the removal of the
  * last entry in the directory -- empty directories are removed.
  */
-static void unlink_entry(char *name, char *last_symlink)
+static void unlink_entry(struct cache_entry *ce)
 {
        char *cp, *prev;
+       char *name = ce->name;
 
-       if (has_symlink_leading_path(name, last_symlink))
+       if (has_symlink_leading_path(ce_namelen(ce), ce->name))
                return;
        if (unlink(name))
                return;
@@ -58,7 +59,6 @@ static int check_updates(struct unpack_trees_options *o)
 {
        unsigned cnt = 0, total = 0;
        struct progress *progress = NULL;
-       char last_symlink[PATH_MAX];
        struct index_state *index = &o->result;
        int i;
        int errs = 0;
@@ -75,14 +75,13 @@ static int check_updates(struct unpack_trees_options *o)
                cnt = 0;
        }
 
-       *last_symlink = '\0';
        for (i = 0; i < index->cache_nr; i++) {
                struct cache_entry *ce = index->cache[i];
 
                if (ce->ce_flags & CE_REMOVE) {
                        display_progress(progress, ++cnt);
                        if (o->update)
-                               unlink_entry(ce->name, last_symlink);
+                               unlink_entry(ce);
                        remove_index_entry_at(&o->result, i);
                        i--;
                        continue;
@@ -97,7 +96,6 @@ static int check_updates(struct unpack_trees_options *o)
                        ce->ce_flags &= ~CE_UPDATE;
                        if (o->update) {
                                errs |= checkout_entry(ce, &state, NULL);
-                               *last_symlink = '\0';
                        }
                }
        }
@@ -553,7 +551,7 @@ static int verify_absent(struct cache_entry *ce, const char *action,
        if (o->index_only || o->reset || !o->update)
                return 0;
 
-       if (has_symlink_leading_path(ce->name, NULL))
+       if (has_symlink_leading_path(ce_namelen(ce), ce->name))
                return 0;
 
        if (!lstat(ce->name, &st)) {