btrfs-progs: Return more meaningful value for btrfs_read_deve_super

btrfs_read_dev_super() only returns 0 or -1, which doesn't really help,
caller won't know if it's caused by bad superblock or superblock out of
range.

Return -errno if pread64() return -1, and return -EOF if none or part of
the super is read out, and return what check_super() returned.

So caller can get -EIO to catch real corrupted super blocks.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/disk-io.c b/disk-io.c
index 854c285..2052bb3 100644 (file)
--- a/disk-io.c
+++ b/disk-io.c
@@ -1590,14 +1590,20 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr,
 
        if (sb_bytenr != BTRFS_SUPER_INFO_OFFSET) {
                ret = pread64(fd, buf, BTRFS_SUPER_INFO_SIZE, sb_bytenr);
+               /* real error */
+               if (ret < 0)
+                       return -errno;
+
+               /* Not large enough sb, return -ENOENT instead of normal -EIO */
                if (ret < BTRFS_SUPER_INFO_SIZE)
-                       return -1;
+                       return -ENOENT;
 
                if (btrfs_super_bytenr(buf) != sb_bytenr)
-                       return -1;
+                       return -EIO;
 
-               if (check_super(buf, sbflags))
-                       return -1;
+               ret = check_super(buf, sbflags);
+               if (ret < 0)
+                       return ret;
                memcpy(sb, buf, BTRFS_SUPER_INFO_SIZE);
                return 0;
        }