libblkid: don't call read() per FAT dir-entry on large disks

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/shlibs/blkid/src/superblocks/vfat.c b/shlibs/blkid/src/superblocks/vfat.c
index 1662f1319ce7b2696be799a6c73b1be8cd36b422..29066c34c0d5a3b2080dd8713cb6ec96edff1cf1 100644 (file)
--- a/shlibs/blkid/src/superblocks/vfat.c
+++ b/shlibs/blkid/src/superblocks/vfat.c
@@ -111,32 +111,59 @@ struct fat32_fsinfo {
 
 static const char *no_name = "NO NAME    ";
 
+/*
+ * Look for LABEL (name) in the FAT root directory.
+ */
 static unsigned char *search_fat_label(blkid_probe pr,
                                uint32_t offset, uint32_t entries)
 {
-       struct vfat_dir_entry *dir;
+       struct vfat_dir_entry *ent, *dir = NULL;
        int i;
 
-       for (i = 0; i < entries; i++) {
+       DBG(DEBUG_LOWPROBE,
+               printf("\tlook for label in root-dir "
+                       "(entries: %d, offset: %d)\n", entries, offset));
 
+       if (!blkid_probe_is_tiny(pr)) {
+               /* large disk, read whole root directory */
                dir = (struct vfat_dir_entry *)
+                       blkid_probe_get_buffer(pr,
+                                       offset,
+                                       entries * sizeof(struct vfat_dir_entry));
+               if (!dir)
+                       return NULL;
+       }
+
+       for (i = 0; i < entries; i++) {
+               /*
+                * The root directory could be relatively large (4-16kB).
+                * Fortunately, the LABEL is usually the first entry in the
+                * directory. On tiny disks we call read() per entry.
+                */
+               if (!dir)
+                       ent = (struct vfat_dir_entry *)
                                blkid_probe_get_extra_buffer(pr,
                                        offset + (i * sizeof(struct vfat_dir_entry)),
                                        sizeof(struct vfat_dir_entry));
-               if (dir->name[0] == 0x00)
+               else
+                       ent = &dir[i];
+
+               if (!ent || ent->name[0] == 0x00)
                        break;
 
-               if ((dir->name[0] == FAT_ENTRY_FREE) ||
-                   (dir->cluster_high != 0 || dir->cluster_low != 0) ||
-                   ((dir->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
+               if ((ent->name[0] == FAT_ENTRY_FREE) ||
+                   (ent->cluster_high != 0 || ent->cluster_low != 0) ||
+                   ((ent->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
                        continue;
 
-               if ((dir->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) ==
+               if ((ent->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) ==
                    FAT_ATTR_VOLUME_ID) {
-                       return dir->name;
+                       DBG(DEBUG_LOWPROBE,
+                               printf("\tfound fs LABEL at entry %d\n", i));
+                       return ent->name;
                }
        }
-       return 0;
+       return NULL;
 }
 
 /*