Am 27.11.2020 um 15:45 hat Vladimir Sementsov-Ogievskiy geschrieben:
> Split out no-perm part of bdrv_set_backing_hd() as a separate
> transaction action. Note the in case of existing BdrvChild we reuse it,
> not recreate, just to do less actions.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
> ---
> block.c | 111 +++++++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 89 insertions(+), 22 deletions(-)
>
> diff --git a/block.c b/block.c
> index 54fb6d24bd..617cba9547 100644
> --- a/block.c
> +++ b/block.c
> @@ -101,6 +101,7 @@ static int bdrv_attach_child_common(BlockDriverState
> *child_bs,
> uint64_t perm, uint64_t shared_perm,
> void *opaque, BdrvChild **child,
> GSList **tran, Error **errp);
> +static void bdrv_remove_backing(BlockDriverState *bs, GSList **tran);
>
> static int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
> BlockReopenQueue
> *queue, Error **errp);
> @@ -3194,45 +3195,111 @@ static BdrvChildRole
> bdrv_backing_role(BlockDriverState *bs)
> }
> }
>
> +typedef struct BdrvSetBackingNoPermState {
> + BlockDriverState *bs;
> + BlockDriverState *backing_bs;
> + BlockDriverState *old_inherits_from;
> + GSList *attach_tran;
> +} BdrvSetBackingNoPermState;
Why do we need the nested attach_tran instead of just including these
actions in the outer transaction?
> +static void bdrv_set_backing_noperm_abort(void *opaque)
> +{
> + BdrvSetBackingNoPermState *s = opaque;
> +
> + if (s->backing_bs) {
> + s->backing_bs->inherits_from = s->old_inherits_from;
> + }
> +
> + tran_abort(s->attach_tran);
> +
> + bdrv_refresh_limits(s->bs, NULL);
> + if (s->old_inherits_from) {
> + bdrv_refresh_limits(s->old_inherits_from, NULL);
> + }
How is bs->inherits_from related to limits? I don't see a
bdrv_refresh_limits() call in bdrv_set_backing_noperm() that this would
undo.
> +}
> +
> +static void bdrv_set_backing_noperm_commit(void *opaque)
> +{
> + BdrvSetBackingNoPermState *s = opaque;
> +
> + tran_commit(s->attach_tran);
> +}
> +
> +static TransactionActionDrv bdrv_set_backing_noperm_drv = {
> + .abort = bdrv_set_backing_noperm_abort,
> + .commit = bdrv_set_backing_noperm_commit,
> + .clean = g_free,
> +};
> +
> /*
> * Sets the bs->backing link of a BDS. A new reference is created; callers
> * which don't need their own reference any more must call bdrv_unref().
> */
> -void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
> - Error **errp)
> +static int bdrv_set_backing_noperm(BlockDriverState *bs,
> + BlockDriverState *backing_bs,
> + GSList **tran, Error **errp)
> {
> - bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
> - bdrv_inherits_from_recursive(backing_hd, bs);
> + int ret = 0;
> + bool update_inherits_from = bdrv_chain_contains(bs, backing_bs) &&
> + bdrv_inherits_from_recursive(backing_bs, bs);
> + GSList *attach_tran = NULL;
> + BdrvSetBackingNoPermState *s;
>
> if (bdrv_is_backing_chain_frozen(bs, child_bs(bs->backing), errp)) {
> - return;
> + return -EPERM;
> }
>
> - if (backing_hd) {
> - bdrv_ref(backing_hd);
> + if (bs->backing && backing_bs) {
> + bdrv_replace_child_safe(bs->backing, backing_bs, tran);
> + } else if (bs->backing && !backing_bs) {
> + bdrv_remove_backing(bs, tran);
> + } else if (backing_bs) {
> + assert(!bs->backing);
> + ret = bdrv_attach_child_noperm(bs, backing_bs, "backing",
> + &child_of_bds, bdrv_backing_role(bs),
> + &bs->backing, &attach_tran, errp);
> + if (ret < 0) {
> + tran_abort(attach_tran);
This looks wrong to me, we'll call tran_abort() a second time through
bdrv_set_backing_noperm_abort() when the outer transaction aborts.
I also notice that the other two if branches do just add things to the
outer 'tran', it's just this branch that gets a nested one.
> + return ret;
> + }
> }
>
> - if (bs->backing) {
> - /* Cannot be frozen, we checked that above */
> - bdrv_unref_child(bs, bs->backing);
> - bs->backing = NULL;
> - }
> + s = g_new(BdrvSetBackingNoPermState, 1);
> + *s = (BdrvSetBackingNoPermState) {
> + .bs = bs,
> + .backing_bs = backing_bs,
> + .old_inherits_from = backing_bs ? backing_bs->inherits_from : NULL,
> + };
> + tran_prepend(tran, &bdrv_set_backing_noperm_drv, s);
>
> - if (!backing_hd) {
> - goto out;
> + /*
> + * If backing_bs was already part of bs's backing chain, and
> + * inherits_from pointed recursively to bs then let's update it to
> + * point directly to bs (else it will become NULL).
Setting it to NULL was previously done by bdrv_unref_child().
bdrv_replace_child_safe() and bdrv_remove_backing() don't seem to do
this any more.
> + */
> + if (backing_bs && update_inherits_from) {
> + backing_bs->inherits_from = bs;
> }
>
> - bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_of_bds,
> - bdrv_backing_role(bs), errp);
> - /* If backing_hd was already part of bs's backing chain, and
> - * inherits_from pointed recursively to bs then let's update it to
> - * point directly to bs (else it will become NULL). */
> - if (bs->backing && update_inherits_from) {
> - backing_hd->inherits_from = bs;
> + bdrv_refresh_limits(bs, NULL);
> +
> + return 0;
> +}
Kevin
