From: Petr Špaček <petr.spacek@nic.cz>
Date: Fri, 9 Oct 2020 09:30:56 +0000 (+0200)
Subject: lib/cache: do not unlink cache lock file
X-Git-Tag: v5.2.0~18^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=97e549bc8c3eb53c632c9799ed7962ee220657ae;p=thirdparty%2Fknot-resolver.git

lib/cache: do not unlink cache lock file

This change serves two purposes:
- removes corner case where lock is deleted and created by another
  instance
- prevents incredibly rare problem where filesystem inodes run out

Beware that lock file is still not created on start-up.
It gets created only when emergency cache clear is executed and stays there.

We might consider creating the file at start-up as well
but that's topic for another MR.
---

diff --git a/lib/cache/cdb_lmdb.c b/lib/cache/cdb_lmdb.c
index f7a4557d3..aef930312 100644
--- a/lib/cache/cdb_lmdb.c
+++ b/lib/cache/cdb_lmdb.c
@@ -517,17 +517,14 @@ static int lockfile_get(const char *path)
 }
 
 /** Release and remove lockfile created by lockfile_get().  Return kr_error(). */
-static int lockfile_release(const char *path, int fd)
+static int lockfile_release(int fd)
 {
-	assert(path && fd > 0); // fd == 0 is surely a mistake, in our case at least
-	int err = 0;
-	// To avoid a race, we unlink it first.
-	if (unlink(path))
-		err = kr_error(errno);
-	// And we try to close it even on error.
-	if (close(fd) && !err)
-		err = kr_error(errno);
-	return err;
+	assert(fd > 0); // fd == 0 is surely a mistake, in our case at least
+	if (close(fd)) {
+		return kr_error(errno);
+	} else {
+		return kr_ok();
+	}
 }
 
 static int cdb_clear(kr_cdb_pt db, struct kr_cdb_stats *stats)
@@ -595,7 +592,7 @@ static int cdb_clear(kr_cdb_pt db, struct kr_cdb_stats *stats)
 	}
 
 	/* Environment updated, release lockfile. */
-	int lrerr = lockfile_release(lockfile, lockfile_fd);
+	int lrerr = lockfile_release(lockfile_fd);
 	if (lrerr) {
 		kr_log_error("[cache] failed to release ./.cachelock: %s\n",
 				kr_strerror(lrerr));