[PATCH] btrfs: Honour FITRIM range constraints during free space trim

[Nikolay Borisov <nborisov@xxxxxxxx>]

Up until now trimming the freespace was done irrespective of what the
arguments of the FITRIM ioctl were. For example fstrim's -o/-l arguments
will be entirely ignored. Fix it by correctly handling those paramter.
This requires breaking if the found freespace extent is after the end of
the passed range as well as completing trim after trimming
fstrim_range::len bytes.

Fixes: 499f377f49f0 ("btrfs: iterate over unused chunk space in FITRIM")
CC: stable@xxxxxxxxxxxxxxx # 4.4+
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
---

Hello, 

Here is a backport to 4.9.y of upstream commit: c2d1b3aae33605a61cbab445d8ae1c708ccd2698
Please apply. 

 fs/btrfs/extent-tree.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7938c48c72ff..6b29165f766f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -11150,9 +11150,9 @@ int btrfs_error_unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
  * transaction.
  */
 static int btrfs_trim_free_extents(struct btrfs_device *device,
-				   u64 minlen, u64 *trimmed)
+				   struct fstrim_range *range, u64 *trimmed)
 {
-	u64 start = 0, len = 0;
+	u64 start = range->start, len = 0;
 	int ret;
 
 	*trimmed = 0;
@@ -11188,8 +11188,8 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
 			atomic_inc(&trans->use_count);
 		spin_unlock(&fs_info->trans_lock);
 
-		ret = find_free_dev_extent_start(trans, device, minlen, start,
-						 &start, &len);
+		ret = find_free_dev_extent_start(trans, device, range->minlen,
+						 start, &start, &len);
 		if (trans)
 			btrfs_put_transaction(trans);
 
@@ -11201,6 +11201,16 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
 			break;
 		}
 
+		/* If we are out of the passed range break */
+		if (start > range->start + range->len - 1) {
+			mutex_unlock(&fs_info->chunk_mutex);
+			ret = 0;
+			break;
+		}
+
+		start = max(range->start, start);
+		len = min(range->len, len);
+
 		ret = btrfs_issue_discard(device->bdev, start, len, &bytes);
 		up_read(&fs_info->commit_root_sem);
 		mutex_unlock(&fs_info->chunk_mutex);
@@ -11211,6 +11221,10 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
 		start += len;
 		*trimmed += bytes;
 
+		/* We've trimmed enough */
+		if (*trimmed >= range->len)
+			break;
+
 		if (fatal_signal_pending(current)) {
 			ret = -ERESTARTSYS;
 			break;
@@ -11295,8 +11309,7 @@ int btrfs_trim_fs(struct btrfs_root *root, struct fstrim_range *range)
 	mutex_lock(&fs_info->fs_devices->device_list_mutex);
 	devices = &fs_info->fs_devices->devices;
 	list_for_each_entry(device, devices, dev_list) {
-		ret = btrfs_trim_free_extents(device, range->minlen,
-					      &group_trimmed);
+		ret = btrfs_trim_free_extents(device, range, &group_trimmed);
 		if (ret) {
 			dev_failed++;
 			dev_ret = ret;
-- 
2.17.1