alternates: use a separate scratch space

The alternate_object_database struct uses a single buffer
both for storing the path to the alternate, and as a scratch
buffer for forming object names. This is efficient (since
otherwise we'd end up storing the path twice), but it makes
life hard for callers who just want to know the path to the
alternate. They have to remember to stop reading after
"alt->name - alt->base" bytes, and to subtract one for the
trailing '/'.

It would be much simpler if they could simply access a
NUL-terminated path string. We could encapsulate this in a
function which puts a NUL in the scratch buffer and returns
the string, but that opens up questions about the lifetime
of the result. The first time another caller uses the
alternate, the scratch buffer may get other data tacked onto
it.

Let's instead just store the root path separately from the
scratch buffer. There aren't enough alternates being stored
for the duplicated data to matter for performance, and this
keeps things simple and safe for the callers.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 055dfdcf9ed89c2052ebbeae53a7b2a92f9e3b70..f01b81eebfebc1c221e81c44e3f14a4e2781f0a7 100644 (file)
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -644,14 +644,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
                fsck_object_dir(get_object_directory());
 
                prepare_alt_odb();
-               for (alt = alt_odb_list; alt; alt = alt->next) {
-                       /* directory name, minus trailing slash */
-                       size_t namelen = alt->name - alt->base - 1;
-                       struct strbuf name = STRBUF_INIT;
-                       strbuf_add(&name, alt->base, namelen);
-                       fsck_object_dir(name.buf);
-                       strbuf_release(&name);
-               }
+               for (alt = alt_odb_list; alt; alt = alt->next)
+                       fsck_object_dir(alt->path);
        }
 
        if (check_full) {

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index e3fdc0aa7883e1050f4fe8a165ec6245ab9abc9e..fd72c90442dca5f1be7bb822ed0579813557c739 100644 (file)
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -492,20 +492,16 @@ static int add_possible_reference_from_superproject(
 {
        struct submodule_alternate_setup *sas = sas_cb;
 
-       /* directory name, minus trailing slash */
-       size_t namelen = alt->name - alt->base - 1;
-       struct strbuf name = STRBUF_INIT;
-       strbuf_add(&name, alt->base, namelen);
-
        /*
         * If the alternate object store is another repository, try the
         * standard layout with .git/modules/<name>/objects
         */
-       if (ends_with(name.buf, ".git/objects")) {
+       if (ends_with(alt->path, ".git/objects")) {
                char *sm_alternate;
                struct strbuf sb = STRBUF_INIT;
                struct strbuf err = STRBUF_INIT;
-               strbuf_add(&sb, name.buf, name.len - strlen("objects"));
+               strbuf_add(&sb, alt->path, strlen(alt->path) - strlen("objects"));
+
                /*
                 * We need to end the new path with '/' to mark it as a dir,
                 * otherwise a submodule name containing '/' will be broken
@@ -533,7 +529,6 @@ static int add_possible_reference_from_superproject(
                strbuf_release(&sb);
        }
 
-       strbuf_release(&name);
        return 0;
 }
 

diff --git a/cache.h b/cache.h
index ece2c7c9b8485eae406276ed22dbaefd9b0bc869..555ba713de6efd9c1d9e5b9bc35fb29521b9dc43 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -1383,8 +1383,11 @@ extern void remove_scheduled_dirs(void);
 
 extern struct alternate_object_database {
        struct alternate_object_database *next;
+
        char *name;
-       char base[FLEX_ARRAY]; /* more */
+       char *scratch;
+
+       char path[FLEX_ARRAY];
 } *alt_odb_list;
 extern void prepare_alt_odb(void);
 extern void read_info_alternates(const char * relative_base, int depth);

diff --git a/sha1_file.c b/sha1_file.c
index b284cea8fb12b1407c275ecfbcbcaf8df2ede6a7..011532a7093c150ba401f6dc48fdbe47bccb1462 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -208,7 +208,7 @@ static const char *alt_sha1_path(struct alternate_object_database *alt,
                                 const unsigned char *sha1)
 {
        fill_sha1_path(alt->name, sha1);
-       return alt->base;
+       return alt->scratch;
 }
 
 /*
@@ -261,8 +261,7 @@ static int alt_odb_usable(struct strbuf *path, const char *normalized_objdir)
         * thing twice, or object directory itself.
         */
        for (alt = alt_odb_list; alt; alt = alt->next) {
-               if (path->len == alt->name - alt->base - 1 &&
-                   !memcmp(path->buf, alt->base, path->len))
+               if (!strcmp(path->buf, alt->path))
                        return 0;
        }
        if (!fspathcmp(path->buf, normalized_objdir))
@@ -401,13 +400,14 @@ struct alternate_object_database *alloc_alt_odb(const char *dir)
        size_t entlen;
 
        entlen = st_add(dirlen, 43); /* '/' + 2 hex + '/' + 38 hex + NUL */
-       ent = xmalloc(st_add(sizeof(*ent), entlen));
-       memcpy(ent->base, dir, dirlen);
+       FLEX_ALLOC_STR(ent, path, dir);
+       ent->scratch = xmalloc(entlen);
+       xsnprintf(ent->scratch, entlen, "%s/", dir);
 
-       ent->name = ent->base + dirlen + 1;
-       ent->base[dirlen] = '/';
-       ent->base[dirlen + 3] = '/';
-       ent->base[entlen-1] = 0;
+       ent->name = ent->scratch + dirlen + 1;
+       ent->scratch[dirlen] = '/';
+       ent->scratch[dirlen + 3] = '/';
+       ent->scratch[entlen-1] = 0;
 
        return ent;
 }
@@ -1485,11 +1485,8 @@ void prepare_packed_git(void)
                return;
        prepare_packed_git_one(get_object_directory(), 1);
        prepare_alt_odb();
-       for (alt = alt_odb_list; alt; alt = alt->next) {
-               alt->name[-1] = 0;
-               prepare_packed_git_one(alt->base, 0);
-               alt->name[-1] = '/';
-       }
+       for (alt = alt_odb_list; alt; alt = alt->next)
+               prepare_packed_git_one(alt->path, 0);
        rearrange_packed_git();
        prepare_packed_git_mru();
        prepare_packed_git_run_once = 1;
@@ -3692,8 +3689,7 @@ static int loose_from_alt_odb(struct alternate_object_database *alt,
        struct strbuf buf = STRBUF_INIT;
        int r;
 
-       /* copy base not including trailing '/' */
-       strbuf_add(&buf, alt->base, alt->name - alt->base - 1);
+       strbuf_addstr(&buf, alt->path);
        r = for_each_loose_file_in_objdir_buf(&buf,
                                              data->cb, NULL, NULL,
                                              data->data);

diff --git a/sha1_name.c b/sha1_name.c
index 98152a68ba472ad319daf18147febfe8154178d2..770ea4fe805969b68fdbc65fed769cc5202440ff 100644 (file)
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -94,12 +94,13 @@ static void find_short_object_filename(int len, const char *hex_pfx, struct disa
        for (alt = fakeent; alt && !ds->ambiguous; alt = alt->next) {
                struct dirent *de;
                DIR *dir;
+
                /*
                 * every alt_odb struct has 42 extra bytes after the base
                 * for exactly this purpose
                 */
                xsnprintf(alt->name, 42, "%.2s/", hex_pfx);
-               dir = opendir(alt->base);
+               dir = opendir(alt->scratch);
                if (!dir)
                        continue;
 

diff --git a/transport.c b/transport.c
index 94d6dc3725a2bb091df66ce6fe266ddd5317ed02..4bc4eeae54ea96bbe48658eb3e6718590fee4350 100644 (file)
--- a/transport.c
+++ b/transport.c
@@ -1084,9 +1084,7 @@ static int refs_from_alternate_cb(struct alternate_object_database *e,
        const struct ref *extra;
        struct alternate_refs_data *cb = data;
 
-       e->name[-1] = '\0';
-       other = xstrdup(real_path(e->base));
-       e->name[-1] = '/';
+       other = xstrdup(real_path(e->path));
        len = strlen(other);
 
        while (other[len-1] == '/')