lstat_cache(): introduce has_symlink_or_noent_leading_path() function

In some cases, especially inside the unpack-trees.c file, and inside
the verify_absent() function, we can avoid some unnecessary calls to
lstat(), if the lstat_cache() function can also be told to keep track
of non-existing directories.

So we update the lstat_cache() function to handle this new fact,
introduce a new wrapper function, and the result is that we save lots
of lstat() calls for a removed directory which previously contained
lots of files, when we call this new wrapper of lstat_cache() instead
of the old one.

We do similar changes inside the unlink_entry() function, since if we
can already say that the leading directory component of a pathname
does not exist, it is not necessary to try to remove a pathname below
it!

Thanks to Junio C Hamano, Linus Torvalds and Rene Scharfe for valuable
comments to this patch!

Signed-off-by: Kjetil Barvik <barvik@broadpark.no>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/cache.h b/cache.h
index 231c06d7726b575f6e522d5b0c0fe43557e8c651..11181aa0079ce94bfbdb2bba77205f49aa3cbcb3 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -720,6 +720,7 @@ struct checkout {
 
 extern int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *topath);
 extern int has_symlink_leading_path(int len, const char *name);
+extern int has_symlink_or_noent_leading_path(int len, const char *name);
 
 extern struct alternate_object_database {
        struct alternate_object_database *next;

diff --git a/symlinks.c b/symlinks.c
index 49fb4d8bc2fc7fba70e18c9d9ec54cb5ba590da5..c69556acf8d41cf0ccf728de732356105e7df0fa 100644 (file)
--- a/symlinks.c
+++ b/symlinks.c
@@ -4,6 +4,7 @@ static struct cache_def {
        char path[PATH_MAX];
        int len;
        int flags;
+       int track_flags;
 } cache;
 
 /*
@@ -30,21 +31,23 @@ static inline int longest_match_lstat_cache(int len, const char *name)
        return match_len;
 }
 
-static inline void reset_lstat_cache(void)
+static inline void reset_lstat_cache(int track_flags)
 {
        cache.path[0] = '\0';
        cache.len = 0;
        cache.flags = 0;
+       cache.track_flags = track_flags;
 }
 
 #define FL_DIR      (1 << 0)
-#define FL_SYMLINK  (1 << 1)
-#define FL_LSTATERR (1 << 2)
-#define FL_ERR      (1 << 3)
+#define FL_NOENT    (1 << 1)
+#define FL_SYMLINK  (1 << 2)
+#define FL_LSTATERR (1 << 3)
+#define FL_ERR      (1 << 4)
 
 /*
  * Check if name 'name' of length 'len' has a symlink leading
- * component, or if the directory exists and is real.
+ * component, or if the directory exists and is real, or not.
  *
  * To speed up the check, some information is allowed to be cached.
  * This can be indicated by the 'track_flags' argument.
@@ -56,25 +59,35 @@ static int lstat_cache(int len, const char *name,
        int match_flags, ret_flags, save_flags, max_len;
        struct stat st;
 
-       /*
-        * Check to see if we have a match from the cache for the
-        * symlink path type.
-        */
-       match_len = last_slash = longest_match_lstat_cache(len, name);
-       match_flags = cache.flags & track_flags & FL_SYMLINK;
-       if (match_flags && match_len == cache.len)
-               return match_flags;
-       /*
-        * If we now have match_len > 0, we would know that the
-        * matched part will always be a directory.
-        *
-        * Also, if we are tracking directories and 'name' is a
-        * substring of the cache on a path component basis, we can
-        * return immediately.
-        */
-       match_flags = track_flags & FL_DIR;
-       if (match_flags && len == match_len)
-               return match_flags;
+       if (cache.track_flags != track_flags) {
+               /*
+                * As a safeguard we clear the cache if the value of
+                * track_flags does not match with the last supplied
+                * value.
+                */
+               reset_lstat_cache(track_flags);
+               match_len = last_slash = 0;
+       } else {
+               /*
+                * Check to see if we have a match from the cache for
+                * the 2 "excluding" path types.
+                */
+               match_len = last_slash = longest_match_lstat_cache(len, name);
+               match_flags = cache.flags & track_flags & (FL_NOENT|FL_SYMLINK);
+               if (match_flags && match_len == cache.len)
+                       return match_flags;
+               /*
+                * If we now have match_len > 0, we would know that
+                * the matched part will always be a directory.
+                *
+                * Also, if we are tracking directories and 'name' is
+                * a substring of the cache on a path component basis,
+                * we can return immediately.
+                */
+               match_flags = track_flags & FL_DIR;
+               if (match_flags && len == match_len)
+                       return match_flags;
+       }
 
        /*
         * Okay, no match from the cache so far, so now we have to
@@ -95,6 +108,8 @@ static int lstat_cache(int len, const char *name,
 
                if (lstat(cache.path, &st)) {
                        ret_flags = FL_LSTATERR;
+                       if (errno == ENOENT)
+                               ret_flags |= FL_NOENT;
                } else if (S_ISDIR(st.st_mode)) {
                        last_slash_dir = last_slash;
                        continue;
@@ -107,11 +122,11 @@ static int lstat_cache(int len, const char *name,
        }
 
        /*
-        * At the end update the cache.  Note that max 2 different
-        * path types, FL_SYMLINK and FL_DIR, can be cached for the
-        * moment!
+        * At the end update the cache.  Note that max 3 different
+        * path types, FL_NOENT, FL_SYMLINK and FL_DIR, can be cached
+        * for the moment!
         */
-       save_flags = ret_flags & track_flags & FL_SYMLINK;
+       save_flags = ret_flags & track_flags & (FL_NOENT|FL_SYMLINK);
        if (save_flags && last_slash > 0 && last_slash < PATH_MAX) {
                cache.path[last_slash] = '\0';
                cache.len = last_slash;
@@ -120,20 +135,20 @@ static int lstat_cache(int len, const char *name,
                   last_slash_dir > 0 && last_slash_dir < PATH_MAX) {
                /*
                 * We have a separate test for the directory case,
-                * since it could be that we have found a symlink and
-                * the track_flags says that we cannot cache this
-                * fact, so the cache would then have been left empty
-                * in this case.
+                * since it could be that we have found a symlink or a
+                * non-existing directory and the track_flags says
+                * that we cannot cache this fact, so the cache would
+                * then have been left empty in this case.
                 *
                 * But if we are allowed to track real directories, we
                 * can still cache the path components before the last
-                * one (the found symlink component).
+                * one (the found symlink or non-existing component).
                 */
                cache.path[last_slash_dir] = '\0';
                cache.len = last_slash_dir;
                cache.flags = FL_DIR;
        } else {
-               reset_lstat_cache();
+               reset_lstat_cache(track_flags);
        }
        return ret_flags;
 }
@@ -147,3 +162,14 @@ int has_symlink_leading_path(int len, const char *name)
                           FL_SYMLINK|FL_DIR) &
                FL_SYMLINK;
 }
+
+/*
+ * Return non-zero if path 'name' has a leading symlink component or
+ * if some leading path component does not exists.
+ */
+int has_symlink_or_noent_leading_path(int len, const char *name)
+{
+       return lstat_cache(len, name,
+                          FL_SYMLINK|FL_NOENT|FL_DIR) &
+               (FL_SYMLINK|FL_NOENT);
+}

diff --git a/unpack-trees.c b/unpack-trees.c
index 54f301da67be879c80426bc21776427fdd38c02e..a3fd383afbe951fea8dbe4378cbe489657843c4a 100644 (file)
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -61,7 +61,7 @@ static void unlink_entry(struct cache_entry *ce)
        char *cp, *prev;
        char *name = ce->name;
 
-       if (has_symlink_leading_path(ce_namelen(ce), ce->name))
+       if (has_symlink_or_noent_leading_path(ce_namelen(ce), ce->name))
                return;
        if (unlink(name))
                return;
@@ -584,7 +584,7 @@ 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_namelen(ce), ce->name))
+       if (has_symlink_or_noent_leading_path(ce_namelen(ce), ce->name))
                return 0;
 
        if (!lstat(ce->name, &st)) {