tree 9977fe8b44a0467bd9f1d942951f0382773af744
parent 12706394bcaa48e3d5e19c97d7b4e5683ebb12fb
author Tao Ma <boyu.mt@taobao.com> 1310356357 -0400
committer Theodore Ts'o <tytso@mit.edu> 1310356357 -0400

ext4: fix trim length underflow with small trim length

In 0f0a25b, we adjust 'len' with s_first_data_block - start, but
it could underflow in case blocksize=1K, fstrim_range.len=512 and
fstrim_range.start = 0. In this case, when we run the code:
len -= first_data_blk - start; len will be underflow to -1ULL.
In the end, although we are safe that last_group check later will limit
the trim to the whole volume, but that isn't what the user really want.

So this patch fix it. It also adds the check for 'start' like ext3 so that
we can break immediately if the start is invalid.

Cc: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>