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 bdrv_set_in_use of now).
Suggest "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> > --- > block.c | 57 > +++++++++++++++++++++++++++++++++++++++++++++++ > include/block/block.h | 6 +++++ > include/block/block_int.h | 5 +++++ > 3 files changed, 68 insertions(+) > > diff --git a/block.c b/block.c > index 13f001a..c1a3576 100644 > --- a/block.c > +++ b/block.c > @@ -4629,6 +4629,63 @@ 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); > + 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; > +} Your interface permits registering multiple blockers, but when you're blocked, you can only find a single blocker (the most recent one, but that's implementation detail). If a need for finding all of them should arise, we'll do it. No change necessary now. [...]