init/do_mounts_rd.c: fix ramdisk identification for padded cramfs

When a cramfs ramdisk padded with 512 bytes is given to the kernel, the
current identify_ramdisk_image function fails to identify it.

Tested with a padded cramfs image on an ARM based board.

Signed-off-by: Neil Armstrong <narmstrong@neotion.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Davidlohr Bueso <dave@gnu.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index fe9acb0ae480..887629e24c54 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -120,6 +120,20 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
         }
 
         /*
+         * Read 512 bytes further to check if cramfs is padded
+         */
+        sys_lseek(fd, start_block * BLOCK_SIZE + 0x200, 0);
+        sys_read(fd, buf, size);
+
+        if (cramfsb->magic == CRAMFS_MAGIC) {
+                printk(KERN_NOTICE
+                       "RAMDISK: cramfs filesystem found at block %d\n",
+                       start_block);
+                nblocks = (cramfsb->size + BLOCK_SIZE - 1) >> BLOCK_SIZE_BITS;
+                goto done;
+        }
+
+        /*
          * Read block 1 to test for minix and ext2 superblock
          */
         sys_lseek(fd, (start_block+1) * BLOCK_SIZE, 0);