Re: [patch] Avoid race in zf_mkdir

[Roman Perepelitsa <roman.perepelitsa@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 621 bytes --]

Perhaps something like this? This should provide the following
guarantees for zf_mkdir -p:

- If it succeeds, the directory must have existed at some point during
the execution of the function (either created by zf_mkdir itself or by
some other concurrent process).
- If it fails, there must have been a point in time during the
execution of the function where the target directory or one of its
parents didn't exist and it was impossible to create it.

`zf_mkdir -p foo` It should work as expected in the face of concurrent
`mkdir foo && rmdir foo` or `touch foo && rm foo`.

I confess that I haven't tested it.

Roman.

[-- Attachment #2: mkdir-patch.txt --]
[-- Type: text/plain, Size: 911 bytes --]

diff --git a/Src/Modules/files.c b/Src/Modules/files.c
index 6d20e38a8..a9ccccb8b 100644
--- a/Src/Modules/files.c
+++ b/Src/Modules/files.c
@@ -122,19 +122,28 @@ domkdir(char *nam, char *path, mode_t mode, int p)
 {
     int err;
     mode_t oumask;
+    struct stat st;
     char const *rpath = unmeta(path);
 
-    if(p) {
-	struct stat st;
-
-	if(!stat(rpath, &st) && S_ISDIR(st.st_mode))
+    while(1) {
+	oumask = umask(0);
+	err = mkdir(rpath, mode) ? errno : 0;
+	umask(oumask);
+	if (!err)
+	    return 0;
+	if(!p || err != EEXIST)
+	    break;
+	if(!stat(rpath, &st)) {
+	    if(errno == ENOENT)
+		continue;
+	    err = errno;
+	    break;
+	}
+	if(S_ISDIR(st.st_mode))
 	    return 0;
+	break;
     }
-    oumask = umask(0);
-    err = mkdir(rpath, mode) ? errno : 0;
-    umask(oumask);
-    if(!err)
-	return 0;
+
     zwarnnam(nam, "cannot make directory `%s': %e", path, err);
     return 1;
 }