Reliable db locking

[netatalk.git] / etc / cnid_dbd / dbif.c

diff --git a/etc/cnid_dbd/dbif.c b/etc/cnid_dbd/dbif.c
index be9b568fe2dc076391f091fa355b779df61ae93c..c79189c504523d801287b7c94b627b8e62800427 100644 (file)
--- a/etc/cnid_dbd/dbif.c
+++ b/etc/cnid_dbd/dbif.c
@@ -20,7 +20,9 @@
 #include <sys/cdefs.h>
 #include <unistd.h>
 #include <atalk/logger.h>
+#include <atalk/util.h>
 #include <db.h>
+
 #include "db_param.h"
 #include "dbif.h"
 #include "pack.h"
@@ -172,6 +174,91 @@ exit:
     return ret;
 }
 
+/*!
+ * Get lock on db lock file
+ *
+ * @args cmd       (r) lock command:
+ *                     LOCK_FREE:   close lockfd
+ *                     LOCK_UNLOCK: unlock lockm keep lockfd open
+ *                     LOCK_EXCL:   F_WRLCK on lockfd
+ *                     LOCK_SHRD:   F_RDLCK on lockfd
+ * @args dbpath    (r) path to lockfile, only used on first call,
+ *                     later the stored fd is used
+ * @returns            LOCK_FREE/LOCK_UNLOCK return 0 on success, -1 on error
+ *                     LOCK_EXCL/LOCK_SHRD return LOCK_EXCL or LOCK_SHRD respectively on
+ *                     success, 0 if the lock couldn't be acquired, -1 on other errors
+ */
+int get_lock(int cmd, const char *dbpath)
+{
+    static int lockfd = -1;
+    int ret;
+    char lockpath[PATH_MAX];
+    struct stat st;
+
+    switch (cmd) {
+    case LOCK_FREE:
+        if (lockfd == -1)
+            return -1;
+        close(lockfd);
+        lockfd = -1;
+        return 0;
+
+    case LOCK_UNLOCK:
+        if (lockfd == -1)
+            return -1;
+        return unlock(lockfd, 0, SEEK_SET, 0);
+
+    case LOCK_EXCL:
+    case LOCK_SHRD:
+        if (lockfd == -1) {
+            if ( (strlen(dbpath) + strlen(LOCKFILENAME+1)) > (PATH_MAX - 1) ) {
+                LOG(log_error, logtype_cnid, ".AppleDB pathname too long");
+                return -1;
+            }
+            strncpy(lockpath, dbpath, PATH_MAX - 1);
+            strcat(lockpath, "/");
+            strcat(lockpath, LOCKFILENAME);
+
+            if ((lockfd = open(lockpath, O_RDWR | O_CREAT, 0644)) < 0) {
+                LOG(log_error, logtype_cnid, "Error opening lockfile: %s", strerror(errno));
+                return -1;
+            }
+
+            if ((stat(dbpath, &st)) != 0) {
+                LOG(log_error, logtype_cnid, "Error statting lockfile: %s", strerror(errno));
+                return -1;
+            }
+
+            if ((chown(lockpath, st.st_uid, st.st_gid)) != 0) {
+                LOG(log_error, logtype_cnid, "Error inheriting lockfile permissions: %s",
+                         strerror(errno));
+                return -1;
+            }
+        }
+    
+        if (cmd == LOCK_EXCL)
+            ret = write_lock(lockfd, 0, SEEK_SET, 0);
+        else
+            ret = read_lock(lockfd, 0, SEEK_SET, 0);
+
+        if (ret != 0) {
+            if (cmd == LOCK_SHRD)
+                LOG(log_error, logtype_cnid, "Volume CNID db is locked, try again...");
+            return 0; 
+        }
+
+        LOG(log_debug, logtype_cnid, "get_lock: got %s lock",
+            cmd == LOCK_EXCL ? "LOCK_EXCL" : "LOCK_SHRD");    
+        return cmd;
+
+    default:
+        return -1;
+    } /* switch(cmd) */
+
+    /* deadc0de, never get here */
+    return -1;
+}
+
 /* --------------- */
 int dbif_stamp(DBD *dbd, void *buffer, int size)
 {