[PATCH v2] ext4: fix to report fstrim.minlen back to userspace

[Chao Yu]

Quoted from manual of fstrim(8):

"-m, --minimum minimum-size
	..., if it's smaller than the device's minimum, and report that
(fstrim_range.minlen) back to userspace."

So this patch tries to report adjusted fstrim_range.minlen back to
userspace via FITRIM interface, if the value is smaller than device's
minimum discard granularity.

Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
---
v2:
- fix the wrong calculation of range->minlen.
 fs/ext4/mballoc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d8b9d6a83d1e..4af51a16fc64 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -6491,6 +6491,10 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
 				discard_granularity >> sb->s_blocksize_bits);
 		if (minlen > EXT4_CLUSTERS_PER_GROUP(sb))
 			goto out;
+
+		/* Report adjusted minlen back to userspace */
+		range->minlen = EXT4_C2B(EXT4_SB(sb), minlen) <<
+						sb->s_blocksize_bits;
 	}
 	if (end >= max_blks - 1) {
 		end = max_blks - 1;
-- 
2.25.1