[libmultipath] scalability fix for devt2devname()

Move from the sysfs /block/*/dev nodes walking in search of maj:min
to a single file walking (/proc/partitions)

Based on idea and initial implementation from Hannes Reinecke, Suse.

diff --git a/libmultipath/discovery.c b/libmultipath/discovery.c
index a196583..3fc9247 100644 (file)
--- a/libmultipath/discovery.c
+++ b/libmultipath/discovery.c
@@ -235,60 +235,54 @@ opennode (char * dev, int mode)
 extern int
 devt2devname (char *devname, char *devt)
 {
-       struct dlist * ls;
-       char attr_path[FILE_NAME_SIZE];
+       FILE *fd;
+       unsigned int tmpmaj, tmpmin, major, minor;
+       char dev[FILE_NAME_SIZE];
        char block_path[FILE_NAME_SIZE];
-       struct sysfs_attribute * attr = NULL;
-       struct sysfs_class * class;
-       struct sysfs_class_device * dev;
+       struct stat statbuf;
 
-       if(safe_sprintf(block_path, "%s/block", sysfs_path)) {
-               condlog(0, "block_path too small");
+       if (sscanf(devt, "%u:%u", &major, &minor) != 2) {
+               condlog(0, "Invalid device number %s", devt);
                return 1;
        }
-       if (!(class = sysfs_open_class("block")))
-               return 1;
 
-       if (!(ls = sysfs_get_class_devices(class)))
-               goto err;
-
-       dlist_for_each_data(ls, dev, struct sysfs_class_device) {
-               if(safe_sprintf(attr_path, "%s/%s/dev",
-                               block_path, dev->name)) {
-                       condlog(0, "attr_path too small");
-                       goto err;
+       if ((fd = fopen("/proc/partitions", "r")) < 0) {
+               condlog(0, "Cannot open /proc/partitions");
+               return 1;
+       }
+       
+       while (!feof(fd)) {
+               int r = fscanf(fd,"%u %u %*d %s",&tmpmaj, &tmpmin, dev);
+               if (!r) {
+                       fscanf(fd,"%*s\n");
+                       continue;
                }
-               if (!(attr = sysfs_open_attribute(attr_path)))
-                       goto err;
-
-               if (sysfs_read_attribute(attr))
-                       goto err1;
-
-               /* discard newline */
-               if (attr->len > 1) attr->len--;
-
-               if (strlen(devt) == attr->len &&
-                   strncmp(attr->value, devt, attr->len) == 0) {
-                       if(safe_sprintf(attr_path, "%s/%s",
-                                       block_path, dev->name)) {
-                               condlog(0, "attr_path too small");
-                               goto err1;
-                       }
-                       sysfs_get_name_from_path(attr_path, devname,
-                                                FILE_NAME_SIZE);
-                       sysfs_close_attribute(attr);
-                       sysfs_close_class(class);
-                       return 0;
+               if (r != 3)
+                       continue;
+               if ((major == tmpmaj) && (minor == tmpmin)) {
+                       sprintf(block_path, "/sys/block/%s", dev);
+                       break;
                }
        }
-err1:
-       sysfs_close_attribute(attr);
-err:
-       sysfs_close_class(class);
-       return 1;
+       fclose(fd);
+
+       if (strncmp(block_path,"/sys/block", 10))
+               return 1;
+
+       if (stat(block_path, &statbuf) < 0) {
+               condlog(0, "No sysfs entry for %s\n", block_path);
+               return 1;
+       }
+
+       if (S_ISDIR(statbuf.st_mode) == 0) {
+               condlog(0, "sysfs entry %s is not a directory\n", block_path);
+               return 1;
+       }
+       strncpy(devname, dev, FILE_NAME_SIZE);
+       return 0;
 }
 
-static int
+int
 do_inq(int sg_fd, int cmddt, int evpd, unsigned int pg_op,
        void *resp, int mx_resp_len, int noisy)
 {