ntfs: add a runlist merge that leaves the source runlist to the caller

ntfs_runlists_merge() frees the source runlist once its runs are in the
destination.  A caller that may have to undo the merge then has to work
out its runs again from the merged runlist, where the first and the
last of them may have been coalesced with neighbouring runs.

Add ntfs_runlists_merge_keep_src(), which neither modifies nor frees
the source runlist.  For that, ntfs_rl_append() and ntfs_rl_replace()
now merge the right-hand end into the copied run in the destination
instead of into the last source run before copying it, and the merge
helpers take the source as const, so the compiler checks that none of
them writes to it.  The merged runlist is the same as before.

For every caller, a source runlist without any mapped run, which the
merge already warns about, now fails with -EINVAL instead of carrying
on with nothing to insert: with no run copied, the right-hand merge
into the destination would index before the insertion point.

The next patch uses ntfs_runlists_merge_keep_src() to free exactly the
clusters it allocated when it has to undo an $MFT data extension.

Suggested-by: Hyunchul Lee <hyc.lee@gmail.com>
Cc: stable@vger.kernel.org # needed by the next patch
Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions