From: David Levine <levinedl@acm.org>
Date: Sun, 16 Sep 2012 18:54:23 +0000 (-0500)
Subject: With mhstore -clobber auto/suffix, when looking for a new filename,
X-Git-Url: http://git.marmaro.de/?a=commitdiff_plain;h=2b7b705f7d986903b6e2190b559e7211e8e79f49;p=mmh

With mhstore -clobber auto/suffix, when looking for a new filename,
actually open(2) the file with O_CREAT | O_EXCL to avoid the race
condition when figuring out the filename first and opening it later.
---

diff --git a/uip/mhstoresbr.c b/uip/mhstoresbr.c
index f5e3347..bcb95ea 100644
--- a/uip/mhstoresbr.c
+++ b/uip/mhstoresbr.c
@@ -1129,7 +1129,7 @@ next_version (char *file, enum clobber_policy_t clobber_policy) {
   }
 
   for (version = 1; version < max_versions; ++version) {
-    struct stat st;
+    int fd;
 
     switch (clobber_policy) {
       case NMH_CLOBBER_AUTO: {
@@ -1151,7 +1151,15 @@ next_version (char *file, enum clobber_policy_t clobber_policy) {
         return NULL;
     }
 
-    if (stat (buffer, &st) == NOTOK) {
+    /* Actually (try to) create the file here to avoid a race
+       condition on file naming + creation.  This won't solve the
+       problem with old NFS that doesn't support O_EXCL, though.
+       Let the umask strip off permissions from 0666 as desired.
+       That's what fopen () would do if it was creating the file. */
+    if ((fd = open (buffer, O_CREAT | O_EXCL,
+                    S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP |
+                    S_IROTH | S_IWOTH)) >= 0) {
+      close (fd);
       break;
     }
   }