Improve is_dm_leaf performance

Read from `/holders` instead of `/slaves` to determine
whether the device is a leaf node, eliminating a scan
across all block devices in the system.

diff --git a/libblkid/src/devname.c b/libblkid/src/devname.c
index 9a173e3489ab8d6611f5e2fbdcd65f16552d0ac5..2e64ddac46b55eae01dccf7c68c03ff16d3920d1 100644 (file)
--- a/libblkid/src/devname.c
+++ b/libblkid/src/devname.c
@@ -149,33 +149,25 @@ done:
 /* Directories where we will try to search for device names */
 static const char *dirlist[] = { "/dev", "/devfs", "/devices", NULL };
 
+/*
+ * Return 1 if the device is a device-mapper 'leaf' node
+ * not holding any other devices in its hierarchy.
+ */
 static int is_dm_leaf(const char *devname)
 {
-       struct dirent   *de, *d_de;
-       DIR             *dir, *d_dir;
+       struct dirent   *de;
+       DIR             *dir;
        char            path[NAME_MAX + 18 + 1];
        int             ret = 1;
 
-       if ((dir = opendir("/sys/block")) == NULL)
+       snprintf(path, sizeof(path), "/sys/block/%s/holders", devname);
+       if ((dir = opendir(path)) == NULL)
                return 0;
        while ((de = readdir(dir)) != NULL) {
-               if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..") ||
-                   !strcmp(de->d_name, devname) ||
-                   strncmp(de->d_name, "dm-", 3) != 0 ||
-                   strlen(de->d_name) > sizeof(path)-32)
+               if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, ".."))
                        continue;
-               snprintf(path, sizeof(path), "/sys/block/%s/slaves", de->d_name);
-               if ((d_dir = opendir(path)) == NULL)
-                       continue;
-               while ((d_de = readdir(d_dir)) != NULL) {
-                       if (!strcmp(d_de->d_name, devname)) {
-                               ret = 0;
-                               break;
-                       }
-               }
-               closedir(d_dir);
-               if (!ret)
-                       break;
+               ret = 0;
+               break;
        }
        closedir(dir);
        return ret;