Fam Zheng <f...@redhat.com> writes:
> BlockDriverState.op_blockers is an array of lists with BLOCK_OP_TYPE_MAX
> elements. Each list is a list of blockers of an operation type
> (BlockOpType), that marks this BDS as currently blocked for a certain
> type of operation with reason errors stored in the list. The rule of
> usage is:
>
> * BDS user who wants to take an operation should check if there's any
> blocker of the type with bdrv_op_is_blocked().
>
> * BDS user who wants to block certain types of operation, should call
> bdrv_op_block (or bdrv_op_block_all to block all types of operations,
> which is similar to the existing bdrv_set_in_use()).
>
> * A blocker is only referenced by op_blockers, so the lifecycle is
> managed by caller, and shouldn't be lost until unblock, so typically
> a caller does these:
>
> - Allocate a blocker with error_setg or similar, call bdrv_op_block()
> to block some operations.
> - Hold the blocker, do his job.
> - Unblock operations that it blocked, with the same reason pointer
> passed to bdrv_op_unblock().
> - Release the blocker with error_free().
>
> Signed-off-by: Fam Zheng <f...@redhat.com>
> Reviewed-by: Benoit Canet <ben...@irqsave.net>
> Reviewed-by: Jeff Cody <jc...@redhat.com>
> ---
> block.c | 75
> +++++++++++++++++++++++++++++++++++++++++++++++
> include/block/block.h | 7 +++++
> include/block/block_int.h | 5 ++++
> 3 files changed, 87 insertions(+)
>
> diff --git a/block.c b/block.c
> index b749d31..32338ca 100644
> --- a/block.c
> +++ b/block.c
> @@ -335,6 +335,7 @@ void bdrv_register(BlockDriver *bdrv)
> BlockDriverState *bdrv_new(const char *device_name, Error **errp)
> {
> BlockDriverState *bs;
> + int i;
>
> if (bdrv_find(device_name)) {
> error_setg(errp, "Device with id '%s' already exists",
> @@ -353,6 +354,9 @@ BlockDriverState *bdrv_new(const char *device_name, Error
> **errp)
> if (device_name[0] != '\0') {
> QTAILQ_INSERT_TAIL(&bdrv_states, bs, device_list);
> }
> + for (i = 0; i < BLOCK_OP_TYPE_MAX; i++) {
> + QLIST_INIT(&bs->op_blockers[i]);
> + }
> bdrv_iostatus_disable(bs);
> notifier_list_init(&bs->close_notifiers);
> notifier_with_return_list_init(&bs->before_write_notifiers);
> @@ -1907,6 +1911,8 @@ static void bdrv_move_feature_fields(BlockDriverState
> *bs_dest,
> pstrcpy(bs_dest->device_name, sizeof(bs_dest->device_name),
> bs_src->device_name);
> bs_dest->device_list = bs_src->device_list;
> + memcpy(bs_dest->op_blockers, bs_src->op_blockers,
> + sizeof(bs_dest->op_blockers));
> }
>
> /*
> @@ -5269,6 +5275,75 @@ void bdrv_unref(BlockDriverState *bs)
> }
> }
>
> +struct BdrvOpBlocker {
> + Error *reason;
> + QLIST_ENTRY(BdrvOpBlocker) list;
> +};
> +
> +bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
> +{
> + BdrvOpBlocker *blocker;
> + assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
Space between cast and its operand is unusual. Please don't respin just
for that.
> + if (!QLIST_EMPTY(&bs->op_blockers[op])) {
> + blocker = QLIST_FIRST(&bs->op_blockers[op]);
> + if (errp) {
> + *errp = error_copy(blocker->reason);
> + }
> + return true;
> + }
> + return false;
> +}
> +
> +void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
> +{
> + BdrvOpBlocker *blocker;
> + assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
> +
> + blocker = g_malloc0(sizeof(BdrvOpBlocker));
Please consider g_new0(), but don't respin just for that.
> + blocker->reason = reason;
> + QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
> +}
[...]
