From: Peter Wang <novalazy@gmail.com>
To: notmuch@notmuchmail.org
Subject: [PATCH v2 15/20] insert: fsync new directory after rename
Date: Sun, 25 Nov 2012 12:16:41 +1100
Message-Id: <1353806206-29133-16-git-send-email-novalazy@gmail.com>
In-Reply-To: <1353806206-29133-1-git-send-email-novalazy@gmail.com>
References: <1353806206-29133-1-git-send-email-novalazy@gmail.com>
Precedence: list

After moving the file from the 'tmp' to the 'new' directory,
fsync on the 'new' directory for durability.
---
 notmuch-insert.c | 39 ++++++++++++++++++++++++++++++++-------
 1 file changed, 32 insertions(+), 7 deletions(-)

diff --git a/notmuch-insert.c b/notmuch-insert.c
index f09c579..831b322 100644
--- a/notmuch-insert.c
+++ b/notmuch-insert.c
@@ -143,10 +143,10 @@ maildir_create_folder (void *ctx, const char *dir)
 /* Open a unique file in the Maildir 'tmp' directory.
  * Returns the file descriptor on success, or -1 on failure.
  * On success, file paths into the 'tmp' and 'new' directories are returned
- * via tmppath and newpath. */
+ * via tmppath and newpath, and the path of the 'new' directory in newdir. */
 static int
 maildir_open_tmp_file (void *ctx, const char *dir,
-		       char **tmppath, char **newpath)
+		       char **tmppath, char **newpath, char **newdir)
 {
     pid_t pid;
     char hostname[256];
@@ -183,8 +183,9 @@ maildir_open_tmp_file (void *ctx, const char *dir,
 	return -1;
     }
 
+    *newdir = talloc_asprintf (ctx, "%s/new", dir);
     *newpath = talloc_asprintf (ctx, "%s/new/%s", dir, filename);
-    if (! *newpath) {
+    if (! *newdir || ! *newpath) {
 	fprintf (stderr, "Out of memory\n");
 	close (fd);
 	unlink (*tmppath);
@@ -204,14 +205,31 @@ maildir_open_tmp_file (void *ctx, const char *dir,
  * http://wiki.dovecot.org/MailboxFormat/Maildir#Mail_delivery
  */
 static notmuch_bool_t
-maildir_move_tmp_to_new (const char *tmppath, const char *newpath)
+maildir_move_tmp_to_new (const char *tmppath, const char *newpath,
+		         const char *newdir)
 {
+    notmuch_bool_t ret;
+    int fd;
+
     if (rename (tmppath, newpath) != 0) {
 	fprintf (stderr, "Error: rename() failed: %s\n", strerror (errno));
 	return FALSE;
     }
 
-    return TRUE;
+    /* Sync the 'new' directory after rename for durability. */
+    ret = TRUE;
+    fd = open (newdir, O_RDONLY);
+    if (fd == -1) {
+	fprintf (stderr, "Error: open() dir failed: %s\n", strerror (errno));
+	ret = FALSE;
+    }
+    if (ret && fsync (fd) != 0) {
+	fprintf (stderr, "Error: fsync() dir failed: %s\n", strerror (errno));
+	ret = FALSE;
+    }
+    if (fd != -1)
+	close (fd);
+    return ret;
 }
 
 /* Copy the contents of fdin into fdout. */
@@ -307,6 +325,12 @@ add_file_to_database (notmuch_database_t *notmuch, const char *path,
 
     notmuch_message_thaw (message);
 
+    /* notmuch_message_tags_to_maildir_flags may rename the message file
+     * once more, and does so without fsyncing the directory afterwards.
+     * rename() is atomic so after a crash the file should appear under
+     * the old or new name. notmuch new should be able to rename the file
+     * again if required, so another fsync is not required, I think.
+     */
     notmuch_message_tags_to_maildir_flags (message);
 
     notmuch_message_destroy (message);
@@ -321,10 +345,11 @@ insert_message (void *ctx, notmuch_database_t *notmuch, int fdin,
 {
     char *tmppath;
     char *newpath;
+    char *newdir;
     int fdout;
     notmuch_bool_t ret;
 
-    fdout = maildir_open_tmp_file (ctx, dir, &tmppath, &newpath);
+    fdout = maildir_open_tmp_file (ctx, dir, &tmppath, &newpath, &newdir);
     if (fdout < 0) {
 	return FALSE;
     }
@@ -335,7 +360,7 @@ insert_message (void *ctx, notmuch_database_t *notmuch, int fdin,
     }
     close (fdout);
     if (ret) {
-	ret = maildir_move_tmp_to_new (tmppath, newpath);
+	ret = maildir_move_tmp_to_new (tmppath, newpath, newdir);
     }
     if (!ret) {
 	unlink (tmppath);
-- 
1.7.12.1