block: Pass truncate exact=true where reasonable

This is a change in behavior, so all instances need a good
justification.  The comments added here should explain my reasoning.

qed already had a comment that suggests it always expected
bdrv_truncate()/blk_truncate() to behave as if exact=true were passed
(c743849bee came eight months before 55b949c847), so it was simply
broken until now.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190918095144.955-8-mreitz@redhat.com
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
[mreitz: Changed comment in qed.c to explain why a new QED file must be
         empty, as requested and suggested by Maxim]
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2019-09-18 11:51:43 +02:00
parent e61a28a9b6
commit e8d04f9237
5 changed files with 31 additions and 7 deletions

View file

@ -5323,7 +5323,11 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
return ret;
}
ret = blk_truncate(blk, new_size, false, PREALLOC_MODE_OFF, errp);
/*
* Amending image options should ensure that the image has
* exactly the given new values, so pass exact=true here.
*/
ret = blk_truncate(blk, new_size, true, PREALLOC_MODE_OFF, errp);
blk_unref(blk);
if (ret < 0) {
return ret;