Merge branch 'mh/safe-create-leading-directories'
authorJunio C Hamano <gitster@pobox.com>
Mon, 27 Jan 2014 18:45:33 +0000 (10:45 -0800)
committerJunio C Hamano <gitster@pobox.com>
Mon, 27 Jan 2014 18:45:33 +0000 (10:45 -0800)
Code clean-up and protection against concurrent write access to the
ref namespace.

* mh/safe-create-leading-directories:
rename_tmp_log(): on SCLD_VANISHED, retry
rename_tmp_log(): limit the number of remote_empty_directories() attempts
rename_tmp_log(): handle a possible mkdir/rmdir race
rename_ref(): extract function rename_tmp_log()
remove_dir_recurse(): handle disappearing files and directories
remove_dir_recurse(): tighten condition for removing unreadable dir
lock_ref_sha1_basic(): if locking fails with ENOENT, retry
lock_ref_sha1_basic(): on SCLD_VANISHED, retry
safe_create_leading_directories(): add new error value SCLD_VANISHED
cmd_init_db(): when creating directories, handle errors conservatively
safe_create_leading_directories(): introduce enum for return values
safe_create_leading_directories(): always restore slash at end of loop
safe_create_leading_directories(): split on first of multiple slashes
safe_create_leading_directories(): rename local variable
safe_create_leading_directories(): add explicit "slash" pointer
safe_create_leading_directories(): reduce scope of local variable
safe_create_leading_directories(): fix format of "if" chaining

builtin/init-db.c
cache.h
dir.c
merge-recursive.c
refs.c
sha1_file.c
index b3f03cf0d6c0f776b2eaba8ff4e1d340216a4463..c7c76bbf21fd5b5c9200b2535875b912e4d49000 100644 (file)
@@ -515,13 +515,14 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
                                saved = shared_repository;
                                shared_repository = 0;
                                switch (safe_create_leading_directories_const(argv[0])) {
-                               case -3:
+                               case SCLD_OK:
+                               case SCLD_PERMS:
+                                       break;
+                               case SCLD_EXISTS:
                                        errno = EEXIST;
                                        /* fallthru */
-                               case -1:
-                                       die_errno(_("cannot mkdir %s"), argv[0]);
-                                       break;
                                default:
+                                       die_errno(_("cannot mkdir %s"), argv[0]);
                                        break;
                                }
                                shared_repository = saved;
diff --git a/cache.h b/cache.h
index 763c961520f93999760d8f24bdb66af2678cca04..dc040fb1aa99b7970e85e5b175e60f862ff6a74a 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -737,8 +737,29 @@ enum sharedrepo {
 };
 int git_config_perm(const char *var, const char *value);
 int adjust_shared_perm(const char *path);
-int safe_create_leading_directories(char *path);
-int safe_create_leading_directories_const(const char *path);
+
+/*
+ * Create the directory containing the named path, using care to be
+ * somewhat safe against races.  Return one of the scld_error values
+ * to indicate success/failure.
+ *
+ * SCLD_VANISHED indicates that one of the ancestor directories of the
+ * path existed at one point during the function call and then
+ * suddenly vanished, probably because another process pruned the
+ * directory while we were working.  To be robust against this kind of
+ * race, callers might want to try invoking the function again when it
+ * returns SCLD_VANISHED.
+ */
+enum scld_error {
+       SCLD_OK = 0,
+       SCLD_FAILED = -1,
+       SCLD_PERMS = -2,
+       SCLD_EXISTS = -3,
+       SCLD_VANISHED = -4
+};
+enum scld_error safe_create_leading_directories(char *path);
+enum scld_error safe_create_leading_directories_const(const char *path);
+
 int mkdir_in_gitdir(const char *path);
 extern void home_config_paths(char **global, char **xdg, char *file);
 extern char *expand_user_path(const char *path);
diff --git a/dir.c b/dir.c
index d10a63f731020aab99f9b25a2b96a029d772410d..b35b6330f850f610b582b189d7e4d6a9ba4495db 100644 (file)
--- a/dir.c
+++ b/dir.c
@@ -1511,8 +1511,13 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
        flag &= ~REMOVE_DIR_KEEP_TOPLEVEL;
        dir = opendir(path->buf);
        if (!dir) {
-               /* an empty dir could be removed even if it is unreadble */
-               if (!keep_toplevel)
+               if (errno == ENOENT)
+                       return keep_toplevel ? -1 : 0;
+               else if (errno == EACCES && !keep_toplevel)
+                       /*
+                        * An empty dir could be removable even if it
+                        * is unreadable:
+                        */
                        return rmdir(path->buf);
                else
                        return -1;
@@ -1528,13 +1533,21 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
 
                strbuf_setlen(path, len);
                strbuf_addstr(path, e->d_name);
-               if (lstat(path->buf, &st))
-                       ; /* fall thru */
-               else if (S_ISDIR(st.st_mode)) {
+               if (lstat(path->buf, &st)) {
+                       if (errno == ENOENT)
+                               /*
+                                * file disappeared, which is what we
+                                * wanted anyway
+                                */
+                               continue;
+                       /* fall thru */
+               } else if (S_ISDIR(st.st_mode)) {
                        if (!remove_dir_recurse(path, flag, &kept_down))
                                continue; /* happy */
-               } else if (!only_empty && !unlink(path->buf))
+               } else if (!only_empty &&
+                          (!unlink(path->buf) || errno == ENOENT)) {
                        continue; /* happy, too */
+               }
 
                /* path too long, stat fails, or non-directory still exists */
                ret = -1;
@@ -1544,7 +1557,7 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
 
        strbuf_setlen(path, original_len);
        if (!ret && !keep_toplevel && !kept_down)
-               ret = rmdir(path->buf);
+               ret = (!rmdir(path->buf) || errno == ENOENT) ? 0 : -1;
        else if (kept_up)
                /*
                 * report the uplevel that it is not an error that we
index a18bd15dd3dcf303909b4b541f35815705a3f50b..8400a8e937d8303ecc2ace1136a0700187865f58 100644 (file)
@@ -693,7 +693,7 @@ static int make_room_for_path(struct merge_options *o, const char *path)
        /* Make sure leading directories are created */
        status = safe_create_leading_directories_const(path);
        if (status) {
-               if (status == -3) {
+               if (status == SCLD_EXISTS) {
                        /* something else exists */
                        error(msg, path, _(": perhaps a D/F conflict?"));
                        return -1;
diff --git a/refs.c b/refs.c
index fc33ee8ffbe917659e36a801ebf7caa1b89a661d..89228e23732ef7e2e83a2e84e82ffb5bd7afec3f 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -2039,6 +2039,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
        int type, lflags;
        int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
        int missing = 0;
+       int attempts_remaining = 3;
 
        lock = xcalloc(1, sizeof(struct ref_lock));
        lock->lock_fd = -1;
@@ -2080,7 +2081,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 
        lock->lk = xcalloc(1, sizeof(struct lock_file));
 
-       lflags = LOCK_DIE_ON_ERROR;
+       lflags = 0;
        if (flags & REF_NODEREF) {
                refname = orig_refname;
                lflags |= LOCK_NODEREF;
@@ -2093,13 +2094,32 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
        if ((flags & REF_NODEREF) && (type & REF_ISSYMREF))
                lock->force_write = 1;
 
-       if (safe_create_leading_directories(ref_file)) {
+ retry:
+       switch (safe_create_leading_directories(ref_file)) {
+       case SCLD_OK:
+               break; /* success */
+       case SCLD_VANISHED:
+               if (--attempts_remaining > 0)
+                       goto retry;
+               /* fall through */
+       default:
                last_errno = errno;
                error("unable to create directory for %s", ref_file);
                goto error_return;
        }
 
        lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
+       if (lock->lock_fd < 0) {
+               if (errno == ENOENT && --attempts_remaining > 0)
+                       /*
+                        * Maybe somebody just deleted one of the
+                        * directories leading to ref_file.  Try
+                        * again:
+                        */
+                       goto retry;
+               else
+                       unable_to_lock_index_die(ref_file, errno);
+       }
        return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
 
  error_return:
@@ -2508,6 +2528,51 @@ int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
  */
 #define TMP_RENAMED_LOG  "logs/refs/.tmp-renamed-log"
 
+static int rename_tmp_log(const char *newrefname)
+{
+       int attempts_remaining = 4;
+
+ retry:
+       switch (safe_create_leading_directories(git_path("logs/%s", newrefname))) {
+       case SCLD_OK:
+               break; /* success */
+       case SCLD_VANISHED:
+               if (--attempts_remaining > 0)
+                       goto retry;
+               /* fall through */
+       default:
+               error("unable to create directory for %s", newrefname);
+               return -1;
+       }
+
+       if (rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", newrefname))) {
+               if ((errno==EISDIR || errno==ENOTDIR) && --attempts_remaining > 0) {
+                       /*
+                        * rename(a, b) when b is an existing
+                        * directory ought to result in ISDIR, but
+                        * Solaris 5.8 gives ENOTDIR.  Sheesh.
+                        */
+                       if (remove_empty_directories(git_path("logs/%s", newrefname))) {
+                               error("Directory not empty: logs/%s", newrefname);
+                               return -1;
+                       }
+                       goto retry;
+               } else if (errno == ENOENT && --attempts_remaining > 0) {
+                       /*
+                        * Maybe another process just deleted one of
+                        * the directories in the path to newrefname.
+                        * Try again from the beginning.
+                        */
+                       goto retry;
+               } else {
+                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
+                               newrefname, strerror(errno));
+                       return -1;
+               }
+       }
+       return 0;
+}
+
 int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
 {
        unsigned char sha1[20], orig_sha1[20];
@@ -2555,30 +2620,9 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
                }
        }
 
-       if (log && safe_create_leading_directories(git_path("logs/%s", newrefname))) {
-               error("unable to create directory for %s", newrefname);
+       if (log && rename_tmp_log(newrefname))
                goto rollback;
-       }
 
- retry:
-       if (log && rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", newrefname))) {
-               if (errno==EISDIR || errno==ENOTDIR) {
-                       /*
-                        * rename(a, b) when b is an existing
-                        * directory ought to result in ISDIR, but
-                        * Solaris 5.8 gives ENOTDIR.  Sheesh.
-                        */
-                       if (remove_empty_directories(git_path("logs/%s", newrefname))) {
-                               error("Directory not empty: logs/%s", newrefname);
-                               goto rollback;
-                       }
-                       goto retry;
-               } else {
-                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
-                               newrefname, strerror(errno));
-                       goto rollback;
-               }
-       }
        logmoved = log;
 
        lock = lock_ref_sha1_basic(newrefname, NULL, 0, NULL);
index e13bd2c3ee7edb4d157e499fbcea80535ec5752f..8b0849f931c5a2f9eea47594b50560fe4526969c 100644 (file)
@@ -105,50 +105,59 @@ int mkdir_in_gitdir(const char *path)
        return adjust_shared_perm(path);
 }
 
-int safe_create_leading_directories(char *path)
+enum scld_error safe_create_leading_directories(char *path)
 {
-       char *pos = path + offset_1st_component(path);
-       struct stat st;
+       char *next_component = path + offset_1st_component(path);
+       enum scld_error ret = SCLD_OK;
+
+       while (ret == SCLD_OK && next_component) {
+               struct stat st;
+               char *slash = strchr(next_component, '/');
 
-       while (pos) {
-               pos = strchr(pos, '/');
-               if (!pos)
+               if (!slash)
                        break;
-               while (*++pos == '/')
-                       ;
-               if (!*pos)
+
+               next_component = slash + 1;
+               while (*next_component == '/')
+                       next_component++;
+               if (!*next_component)
                        break;
-               *--pos = '\0';
+
+               *slash = '\0';
                if (!stat(path, &st)) {
                        /* path exists */
-                       if (!S_ISDIR(st.st_mode)) {
-                               *pos = '/';
-                               return -3;
-                       }
-               }
-               else if (mkdir(path, 0777)) {
+                       if (!S_ISDIR(st.st_mode))
+                               ret = SCLD_EXISTS;
+               } else if (mkdir(path, 0777)) {
                        if (errno == EEXIST &&
-                           !stat(path, &st) && S_ISDIR(st.st_mode)) {
+                           !stat(path, &st) && S_ISDIR(st.st_mode))
                                ; /* somebody created it since we checked */
-                       } else {
-                               *pos = '/';
-                               return -1;
-                       }
-               }
-               else if (adjust_shared_perm(path)) {
-                       *pos = '/';
-                       return -2;
+                       else if (errno == ENOENT)
+                               /*
+                                * Either mkdir() failed because
+                                * somebody just pruned the containing
+                                * directory, or stat() failed because
+                                * the file that was in our way was
+                                * just removed.  Either way, inform
+                                * the caller that it might be worth
+                                * trying again:
+                                */
+                               ret = SCLD_VANISHED;
+                       else
+                               ret = SCLD_FAILED;
+               } else if (adjust_shared_perm(path)) {
+                       ret = SCLD_PERMS;
                }
-               *pos++ = '/';
+               *slash = '/';
        }
-       return 0;
+       return ret;
 }
 
-int safe_create_leading_directories_const(const char *path)
+enum scld_error safe_create_leading_directories_const(const char *path)
 {
        /* path points to cache entries, so xstrdup before messing with it */
        char *buf = xstrdup(path);
-       int result = safe_create_leading_directories(buf);
+       enum scld_error result = safe_create_leading_directories(buf);
        free(buf);
        return result;
 }