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2021-02-03block/nbd: only enter connection coroutine if it's presentRoman Kagan
When an NBD block driver state is moved from one aio_context to another (e.g. when doing a drain in a migration thread), nbd_client_attach_aio_context_bh is executed that enters the connection coroutine. However, the assumption that ->connection_co is always present here appears incorrect: the connection may have encountered an error other than -EIO in the underlying transport, and thus may have decided to quit rather than keep trying to reconnect, and therefore it may have terminated the connection coroutine. As a result an attempt to reassign the client in this state (NBD_CLIENT_QUIT) to a different aio_context leads to a null pointer dereference: #0 qio_channel_detach_aio_context (ioc=0x0) at /build/qemu-gYtjVn/qemu-5.0.1/io/channel.c:452 #1 0x0000562a242824b3 in bdrv_detach_aio_context (bs=0x562a268d6a00) at /build/qemu-gYtjVn/qemu-5.0.1/block.c:6151 #2 bdrv_set_aio_context_ignore (bs=bs@entry=0x562a268d6a00, new_context=new_context@entry=0x562a260c9580, ignore=ignore@entry=0x7feeadc9b780) at /build/qemu-gYtjVn/qemu-5.0.1/block.c:6230 #3 0x0000562a24282969 in bdrv_child_try_set_aio_context (bs=bs@entry=0x562a268d6a00, ctx=0x562a260c9580, ignore_child=<optimized out>, errp=<optimized out>) at /build/qemu-gYtjVn/qemu-5.0.1/block.c:6332 #4 0x0000562a242bb7db in blk_do_set_aio_context (blk=0x562a2735d0d0, new_context=0x562a260c9580, update_root_node=update_root_node@entry=true, errp=errp@entry=0x0) at /build/qemu-gYtjVn/qemu-5.0.1/block/block-backend.c:1989 #5 0x0000562a242be0bd in blk_set_aio_context (blk=<optimized out>, new_context=<optimized out>, errp=errp@entry=0x0) at /build/qemu-gYtjVn/qemu-5.0.1/block/block-backend.c:2010 #6 0x0000562a23fbd953 in virtio_blk_data_plane_stop (vdev=<optimized out>) at /build/qemu-gYtjVn/qemu-5.0.1/hw/block/dataplane/virtio-blk.c:292 #7 0x0000562a241fc7bf in virtio_bus_stop_ioeventfd (bus=0x562a260dbf08) at /build/qemu-gYtjVn/qemu-5.0.1/hw/virtio/virtio-bus.c:245 #8 0x0000562a23fefb2e in virtio_vmstate_change (opaque=0x562a260dbf90, running=0, state=<optimized out>) at /build/qemu-gYtjVn/qemu-5.0.1/hw/virtio/virtio.c:3220 #9 0x0000562a2402ebfd in vm_state_notify (running=running@entry=0, state=state@entry=RUN_STATE_FINISH_MIGRATE) at /build/qemu-gYtjVn/qemu-5.0.1/softmmu/vl.c:1275 #10 0x0000562a23f7bc02 in do_vm_stop (state=RUN_STATE_FINISH_MIGRATE, send_stop=<optimized out>) at /build/qemu-gYtjVn/qemu-5.0.1/cpus.c:1032 #11 0x0000562a24209765 in migration_completion (s=0x562a260e83a0) at /build/qemu-gYtjVn/qemu-5.0.1/migration/migration.c:2914 #12 migration_iteration_run (s=0x562a260e83a0) at /build/qemu-gYtjVn/qemu-5.0.1/migration/migration.c:3275 #13 migration_thread (opaque=opaque@entry=0x562a260e83a0) at /build/qemu-gYtjVn/qemu-5.0.1/migration/migration.c:3439 #14 0x0000562a2435ca96 in qemu_thread_start (args=<optimized out>) at /build/qemu-gYtjVn/qemu-5.0.1/util/qemu-thread-posix.c:519 #15 0x00007feed31466ba in start_thread (arg=0x7feeadc9c700) at pthread_create.c:333 #16 0x00007feed2e7c41d in __GI___sysctl (name=0x0, nlen=608471908, oldval=0x562a2452b138, oldlenp=0x0, newval=0x562a2452c5e0 <__func__.28102>, newlen=0) at ../sysdeps/unix/sysv/linux/sysctl.c:30 #17 0x0000000000000000 in ?? () Fix it by checking that the connection coroutine is non-null before trying to enter it. If it is null, no entering is needed, as the connection is probably going down anyway. Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210129073859.683063-3-rvkagan@yandex-team.ru> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/nbd: only detach existing iochannel from aio_contextRoman Kagan
When the reconnect in NBD client is in progress, the iochannel used for NBD connection doesn't exist. Therefore an attempt to detach it from the aio_context of the parent BlockDriverState results in a NULL pointer dereference. The problem is triggerable, in particular, when an outgoing migration is about to finish, and stopping the dataplane tries to move the BlockDriverState from the iothread aio_context to the main loop. If the NBD connection is lost before this point, and the NBD client has entered the reconnect procedure, QEMU crashes: #0 qemu_aio_coroutine_enter (ctx=0x5618056c7580, co=0x0) at /build/qemu-6MF7tq/qemu-5.0.1/util/qemu-coroutine.c:109 #1 0x00005618034b1b68 in nbd_client_attach_aio_context_bh ( opaque=0x561805ed4c00) at /build/qemu-6MF7tq/qemu-5.0.1/block/nbd.c:164 #2 0x000056180353116b in aio_wait_bh (opaque=0x7f60e1e63700) at /build/qemu-6MF7tq/qemu-5.0.1/util/aio-wait.c:55 #3 0x0000561803530633 in aio_bh_call (bh=0x7f60d40a7e80) at /build/qemu-6MF7tq/qemu-5.0.1/util/async.c:136 #4 aio_bh_poll (ctx=ctx@entry=0x5618056c7580) at /build/qemu-6MF7tq/qemu-5.0.1/util/async.c:164 #5 0x0000561803533e5a in aio_poll (ctx=ctx@entry=0x5618056c7580, blocking=blocking@entry=true) at /build/qemu-6MF7tq/qemu-5.0.1/util/aio-posix.c:650 #6 0x000056180353128d in aio_wait_bh_oneshot (ctx=0x5618056c7580, cb=<optimized out>, opaque=<optimized out>) at /build/qemu-6MF7tq/qemu-5.0.1/util/aio-wait.c:71 #7 0x000056180345c50a in bdrv_attach_aio_context (new_context=0x5618056c7580, bs=0x561805ed4c00) at /build/qemu-6MF7tq/qemu-5.0.1/block.c:6172 #8 bdrv_set_aio_context_ignore (bs=bs@entry=0x561805ed4c00, new_context=new_context@entry=0x5618056c7580, ignore=ignore@entry=0x7f60e1e63780) at /build/qemu-6MF7tq/qemu-5.0.1/block.c:6237 #9 0x000056180345c969 in bdrv_child_try_set_aio_context ( bs=bs@entry=0x561805ed4c00, ctx=0x5618056c7580, ignore_child=<optimized out>, errp=<optimized out>) at /build/qemu-6MF7tq/qemu-5.0.1/block.c:6332 #10 0x00005618034957db in blk_do_set_aio_context (blk=0x56180695b3f0, new_context=0x5618056c7580, update_root_node=update_root_node@entry=true, errp=errp@entry=0x0) at /build/qemu-6MF7tq/qemu-5.0.1/block/block-backend.c:1989 #11 0x00005618034980bd in blk_set_aio_context (blk=<optimized out>, new_context=<optimized out>, errp=errp@entry=0x0) at /build/qemu-6MF7tq/qemu-5.0.1/block/block-backend.c:2010 #12 0x0000561803197953 in virtio_blk_data_plane_stop (vdev=<optimized out>) at /build/qemu-6MF7tq/qemu-5.0.1/hw/block/dataplane/virtio-blk.c:292 #13 0x00005618033d67bf in virtio_bus_stop_ioeventfd (bus=0x5618056d9f08) at /build/qemu-6MF7tq/qemu-5.0.1/hw/virtio/virtio-bus.c:245 #14 0x00005618031c9b2e in virtio_vmstate_change (opaque=0x5618056d9f90, running=0, state=<optimized out>) at /build/qemu-6MF7tq/qemu-5.0.1/hw/virtio/virtio.c:3220 #15 0x0000561803208bfd in vm_state_notify (running=running@entry=0, state=state@entry=RUN_STATE_FINISH_MIGRATE) at /build/qemu-6MF7tq/qemu-5.0.1/softmmu/vl.c:1275 #16 0x0000561803155c02 in do_vm_stop (state=RUN_STATE_FINISH_MIGRATE, send_stop=<optimized out>) at /build/qemu-6MF7tq/qemu-5.0.1/cpus.c:1032 #17 0x00005618033e3765 in migration_completion (s=0x5618056e6960) at /build/qemu-6MF7tq/qemu-5.0.1/migration/migration.c:2914 #18 migration_iteration_run (s=0x5618056e6960) at /build/qemu-6MF7tq/qemu-5.0.1/migration/migration.c:3275 #19 migration_thread (opaque=opaque@entry=0x5618056e6960) at /build/qemu-6MF7tq/qemu-5.0.1/migration/migration.c:3439 #20 0x0000561803536ad6 in qemu_thread_start (args=<optimized out>) at /build/qemu-6MF7tq/qemu-5.0.1/util/qemu-thread-posix.c:519 #21 0x00007f61085d06ba in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0 #22 0x00007f610830641d in sysctl () from /lib/x86_64-linux-gnu/libc.so.6 #23 0x0000000000000000 in ?? () Fix it by checking that the iochannel is non-null before trying to detach it from the aio_context. If it is null, no detaching is needed, and it will get reattached in the proper aio_context once the connection is reestablished. Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210129073859.683063-2-rvkagan@yandex-team.ru> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: use int64_t bytes in copy_rangeVladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, convert now copy_range parameters which are already 64bit to signed type. It's safe as we don't work with requests overflowing BDRV_MAX_LENGTH (which is less than INT64_MAX), and do check the requests in bdrv_co_copy_range_internal() (by bdrv_check_request32(), which calls bdrv_check_request()). Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-17-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: support int64_t bytes in read/write wrappersVladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). Now, since bdrv_co_preadv_part() and bdrv_co_pwritev_part() have been updated, update all their wrappers. For all of them type of 'bytes' is widening, so callers are safe. We have update request_fn in blkverify.c simultaneously. Still it's just a pointer to one of bdrv_co_pwritev() or bdrv_co_preadv(), and type is widening for callers of the request_fn anyway. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-16-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: grammar tweak] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: support int64_t bytes in bdrv_co_p{read,write}v_part()Vladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, prepare bdrv_co_preadv_part() and bdrv_co_pwritev_part() and their remaining dependencies now. bdrv_pad_request() is updated simultaneously, as pointer to bytes passed to it both from bdrv_co_pwritev_part() and bdrv_co_preadv_part(). So, all callers of bdrv_pad_request() are updated to pass 64bit bytes. bdrv_pad_request() is already good for 64bit requests, add corresponding assertion. Look at bdrv_co_preadv_part() and bdrv_co_pwritev_part(). Type is widening, so callers are safe. Let's look inside the functions. In bdrv_co_preadv_part() and bdrv_aligned_pwritev() we only pass bytes to other already int64_t interfaces (and some obviously safe calculations), it's OK. In bdrv_co_do_zero_pwritev() aligned_bytes may become large now, still it's passed to bdrv_aligned_pwritev which supports int64_t bytes. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-15-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: support int64_t bytes in bdrv_aligned_preadv()Vladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, prepare bdrv_aligned_preadv() now. Make the bytes variable in bdrv_padding_rmw_read() int64_t, as it is only used for pass-through to bdrv_aligned_preadv(). All bdrv_aligned_preadv() callers are safe as type is widening. Let's look inside: - add a new-style assertion that request is good. - callees bdrv_is_allocated(), bdrv_co_do_copy_on_readv() supports int64_t bytes - conversion of bytes_remaining is OK, as we never have requests overflowing BDRV_MAX_LENGTH - looping through bytes_remaining is ok, num is updated to int64_t - for bdrv_driver_preadv we have same limit of max_transfer - qemu_iovec_memset is OK, as bytes+qiov_offset should not overflow qiov->size anyway (thanks to bdrv_check_qiov_request()) Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-14-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: grammar tweak] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: support int64_t bytes in bdrv_co_do_copy_on_readv()Vladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, prepare bdrv_co_do_copy_on_readv() now. 'bytes' type widening, so callers are safe. Look at the function itself: bytes, skip_bytes and progress become int64_t. bdrv_round_to_clusters() is OK, cluster_bytes now may be large. trace_bdrv_co_do_copy_on_readv() is OK looping through cluster_bytes is still OK. pnum is still capped to max_transfer, and to MAX_BOUNCE_BUFFER when we are going to do COR operation. Therefor calculations in qemu_iovec_from_buf() and bdrv_driver_preadv() should not change. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-13-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: support int64_t bytes in bdrv_aligned_pwritev()Vladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, prepare bdrv_aligned_pwritev() now and convert the dependencies: bdrv_co_write_req_prepare() and bdrv_co_write_req_finish() to signed type bytes. Conversion of bdrv_co_write_req_prepare() and bdrv_co_write_req_finish() is definitely safe, as all requests in block/io must not overflow BDRV_MAX_LENGTH. Still add assertions. For bdrv_aligned_pwritev() 'bytes' type is widened, so callers are safe. Let's check usage of the parameter inside the function. Passing to bdrv_co_write_req_prepare() and bdrv_co_write_req_finish() is OK. Passing to qemu_iovec_* is OK after new assertion. All other callees are already updated to int64_t. Checking alignment is not changed, offset + bytes and qiov_offset + bytes calculations are safe (thanks to new assertions). max_transfer is kept to be int for now. It has a default of INT_MAX here, and some drivers may rely on it. It's to be refactored later. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-12-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: support int64_t bytes in bdrv_co_do_pwrite_zeroes()Vladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, prepare bdrv_co_do_pwrite_zeroes() now. Callers are safe, as converting int to int64_t is safe. Concentrate on 'bytes' usage in the function (thx to Eric Blake): compute 'int tail' via % 'int alignment' - safe fragmentation loop 'int num' - still fragments with a cap on max_transfer use of 'num' within the loop MIN(bytes, max_transfer) as well as %alignment - still works, so calculations in if (head) {} are safe clamp size by 'int max_write_zeroes' - safe drv->bdrv_co_pwrite_zeroes(int) - safe because of clamping clamp size by 'int max_transfer' - safe buf allocation is still clamped to max_transfer qemu_iovec_init_buf(size_t) - safe because of clamping bdrv_driver_pwritev(uint64_t) - safe Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-11-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: use int64_t bytes in driver wrappersVladimir Sementsov-Ogievskiy
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, convert driver wrappers parameters which are already 64bit to signed type. Requests in block/io.c must never exceed BDRV_MAX_LENGTH (which is less than INT64_MAX), which makes the conversion to signed 64bit type safe. Add corresponding assertions. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-10-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block: use int64_t as bytes type in tracked requestsEric Blake
We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). All requests in block/io must not overflow BDRV_MAX_LENGTH, all external users of BdrvTrackedRequest already have corresponding assertions, so we are safe. Add some assertions still. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-9-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: improve bdrv_check_request: check qiov tooVladimir Sementsov-Ogievskiy
Operations with qiov add more restrictions on bytes, let's cover it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-8-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytesVladimir Sementsov-Ogievskiy
The function is called from 64bit io handlers, and bytes is just passed to throttle_account() which is 64bit too (unsigned though). So, let's convert intermediate argument to 64bit too. This patch is a first in the 64-bit-blocklayer series, so we are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). Patch-correctness audit by Eric Blake: Caller has 32-bit, this patch now causes widening which is safe: block/block-backend.c: blk_do_preadv() passes 'unsigned int' block/block-backend.c: blk_do_pwritev_part() passes 'unsigned int' block/throttle.c: throttle_co_pwrite_zeroes() passes 'int' block/throttle.c: throttle_co_pdiscard() passes 'int' Caller has 64-bit, this patch fixes potential bug where pre-patch could narrow, except it's easy enough to trace that callers are still capped at 2G actions: block/throttle.c: throttle_co_preadv() passes 'uint64_t' block/throttle.c: throttle_co_pwritev() passes 'uint64_t' Implementation in question: block/throttle-groups.c throttle_group_co_io_limits_intercept() takes 'unsigned int bytes' and uses it: argument to util/throttle.c throttle_account(uint64_t) All safe: it patches a latent bug, and does not introduce any 64-bit gotchas once throttle_co_p{read,write}v are relaxed, and assuming throttle_account() is not buggy. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Alberto Garcia <berto@igalia.com> Message-Id: <20201211183934.169161-7-vsementsov@virtuozzo.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: bdrv_pad_request(): support qemu_iovec_init_extended failureVladimir Sementsov-Ogievskiy
Make bdrv_pad_request() honest: return error if qemu_iovec_init_extended() failed. Update also bdrv_padding_destroy() to clean the structure for safety. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-6-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block/io: refactor bdrv_pad_request(): move bdrv_pad_request() upVladimir Sementsov-Ogievskiy
Prepare for the following patch when bdrv_pad_request() will be able to fail. Update the comments. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-5-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: grammar tweak] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block: fix theoretical overflow in bdrv_init_padding()Vladimir Sementsov-Ogievskiy
Calculation of sum may theoretically overflow, so use 64bit type and add some good assertions. Use int64_t constantly. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-4-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: tweak assertion order] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03util/iov: make qemu_iovec_init_extended() honestVladimir Sementsov-Ogievskiy
Actually, we can't extend the io vector in all cases. Handle possible MAX_IOV and size_t overflows. For now add assertion to callers (actually they rely on success anyway) and fix them in the following patch. Add also some additional good assertions to qemu_iovec_init_slice() while being here. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-3-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-03block: refactor bdrv_check_request: add errpVladimir Sementsov-Ogievskiy
It's better to pass &error_abort than just assert that result is 0: on crash, we'll immediately see the reason in the backtrace. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201211183934.169161-2-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: fix iotest 206 fallout] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-02-02block: Fix VM size column width in bdrv_snapshot_dump()Kevin Wolf
size_to_str() can return a size like "4.24 MiB", with a single digit integer part and two fractional digits. This is eight characters, but commit b39847a5 changed the format string to only reserve seven characters for the column. This can result in unaligned columns, which in turn changes the output of iotests case 267 because exceeding the column size defeats the attempt to filter the size out of the output (observed with the ppc64 emulator). The resulting change is only a whitespace change, but since commit f203080b this is enough for iotests to consider the test failed. Taking a character away from the tag name column and adding it to the VM size column doesn't change anything in the common case (the tag name is left justified, the VM size is right justified), but fixes this case. Fixes: b39847a50553b7679d6d7fefbe6a108a17aacf8d Signed-off-by: Kevin Wolf <kwolf@redhat.com> Message-Id: <20210202155911.179865-1-kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2021-02-02block/nvme: Trace NVMe spec version supported by the controllerPhilippe Mathieu-Daudé
NVMe controllers implement different versions of the spec, and different features of it. It is useful to gather this information when debugging. Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com> Message-Id: <20210127212137.3482291-3-philmd@redhat.com> Reviewed-by: Klaus Jensen <k.jensen@samsung.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2021-02-02block/nvme: Properly display doorbell stride length in trace eventPhilippe Mathieu-Daudé
Commit 15b2260bef3 ("block/nvme: Trace controller capabilities") misunderstood the doorbell stride value from the datasheet, use the correct one. The 'doorbell_scale' variable used few lines later is correct. Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com> Message-Id: <20210127212137.3482291-2-philmd@redhat.com> Reviewed-by: Klaus Jensen <k.jensen@samsung.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2021-01-28Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2021-01-28' into ↵Peter Maydell
staging QAPI patches patches for 2021-01-28 # gpg: Signature made Thu 28 Jan 2021 07:10:21 GMT # gpg: using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653 # gpg: issuer "armbru@redhat.com" # gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full] # gpg: aka "Markus Armbruster <armbru@pond.sub.org>" [full] # Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867 4E5F 3870 B400 EB91 8653 * remotes/armbru/tags/pull-qapi-2021-01-28: qapi: More complex uses of QAPI_LIST_APPEND qapi: Use QAPI_LIST_APPEND in trivial cases qapi: Introduce QAPI_LIST_APPEND qapi: A couple more QAPI_LIST_PREPEND() stragglers net: Clarify early exit condition Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2021-01-28qapi: More complex uses of QAPI_LIST_APPENDEric Blake
These cases require a bit more thought to review; in each case, the code was appending to a list, but not with a FOOList **tail variable. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210113221013.390592-6-eblake@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> [Flawed change to qmp_guest_network_get_interfaces() dropped] Signed-off-by: Markus Armbruster <armbru@redhat.com>
2021-01-28qapi: Use QAPI_LIST_APPEND in trivial casesEric Blake
The easiest spots to use QAPI_LIST_APPEND are where we already have an obvious pointer to the tail of a list. While at it, consistently use the variable name 'tail' for that purpose. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20210113221013.390592-5-eblake@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>
2021-01-27block: Separate blk_is_writable() and blk_supports_write_perm()Kevin Wolf
Currently, blk_is_read_only() tells whether a given BlockBackend can only be used in read-only mode because its root node is read-only. Some callers actually try to answer a slightly different question: Is the BlockBackend configured to be writable, by taking write permissions on the root node? This can differ, for example, for CD-ROM devices which don't take write permissions, but may be backed by a writable image file. scsi-cd allows write requests to the drive if blk_is_read_only() returns false. However, the write request will immediately run into an assertion failure because the write permission is missing. This patch introduces separate functions for both questions. blk_supports_write_perm() answers the question whether the block node/image file can support writable devices, whereas blk_is_writable() tells whether the BlockBackend is currently configured to be writable. All calls of blk_is_read_only() are converted to one of the two new functions. Fixes: https://bugs.launchpad.net/bugs/1906693 Cc: qemu-stable@nongnu.org Signed-off-by: Kevin Wolf <kwolf@redhat.com> Message-Id: <20210118123448.307825-2-kwolf@redhat.com> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2021-01-26block: report errno when flock fcntl failsDavid Edmondson
When a call to fcntl(2) for the purpose of adding file locks fails with an error other than EAGAIN or EACCES, report the error returned by fcntl. EAGAIN or EACCES are elided as they are considered to be common failures, indicating that a conflicting lock is held by another process. No errors are elided when removing file locks. Signed-off-by: David Edmondson <david.edmondson@oracle.com> Message-Id: <20210113164447.2545785-1-david.edmondson@oracle.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: drop unused argument of block_copy()Vladimir Sementsov-Ogievskiy
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-21-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: drop unused block_copy_set_progress_callback()Vladimir Sementsov-Ogievskiy
Drop unused code. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-20-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26backup: move to block-copyVladimir Sementsov-Ogievskiy
This brings async request handling and block-status driven chunk sizes to backup out of the box, which improves backup performance. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-18-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/backup: drop extra gotos from backup_run()Vladimir Sementsov-Ogievskiy
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-17-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: make progress_bytes_callback optionalVladimir Sementsov-Ogievskiy
We are going to stop use of this callback in the following commit. Still the callback handling code will be dropped in a separate commit. So, for now let's make it optional. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-16-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26qapi: backup: add max-chunk and max-workers to x-perf structVladimir Sementsov-Ogievskiy
Add new parameters to configure future backup features. The patch doesn't introduce aio backup requests (so we actually have only one worker) neither requests larger than one cluster. Still, formally we satisfy these maximums anyway, so add the parameters now, to facilitate further patch which will really change backup job behavior. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-11-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: add block_copy_cancelVladimir Sementsov-Ogievskiy
Add function to cancel running async block-copy call. It will be used in backup. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-8-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: add ratelimit to block-copyVladimir Sementsov-Ogievskiy
We are going to directly use one async block-copy operation for backup job, so we need rate limiter. We want to maintain current backup behavior: only background copying is limited and copy-before-write operations only participate in limit calculation. Therefore we need one rate limiter for block-copy state and boolean flag for block-copy call state for actual limitation. Note, that we can't just calculate each chunk in limiter after successful copying: it will not save us from starting a lot of async sub-requests which will exceed limit too much. Instead let's use the following scheme on sub-request creation: 1. If at the moment limit is not exceeded, create the request and account it immediately. 2. If at the moment limit is already exceeded, drop create sub-request and handle limit instead (by sleep). With this approach we'll never exceed the limit more than by one sub-request (which pretty much matches current backup behavior). Note also, that if there is in-flight block-copy async call, block_copy_kick() should be used after set-speed to apply new setup faster. For that block_copy_kick() published in this patch. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-7-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: add list of all call-statesVladimir Sementsov-Ogievskiy
It simplifies debugging. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-6-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: add max_chunk and max_workers parametersVladimir Sementsov-Ogievskiy
They will be used for backup. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-5-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: implement block_copy_asyncVladimir Sementsov-Ogievskiy
We'll need async block-copy invocation to use in backup directly. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-4-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/block-copy: More explicit call_stateVladimir Sementsov-Ogievskiy
Refactor common path to use BlockCopyCallState pointer as parameter, to prepare it for use in asynchronous block-copy (at least, we'll need to run block-copy in a coroutine, passing the whole parameters as one pointer). Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-3-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26qapi: backup: add perf.use-copy-range parameterVladimir Sementsov-Ogievskiy
Experiments show, that copy_range is not always making things faster. So, to make experimentation simpler, let's add a parameter. Some more perf parameters will be added soon, so here is a new struct. For now, add new backup qmp parameter with x- prefix for the following reasons: - We are going to add more performance parameters, some will be related to the whole block-copy process, some only to background copying in backup (ignored for copy-before-write operations). - On the other hand, we are going to use block-copy interface in other block jobs, which will need performance options as well.. And it should be the same structure or at least somehow related. So, there are too much unclean things about how the interface and now we need the new options mostly for testing. Let's keep them experimental for a while. In do_backup_common() new x-perf parameter handled in a way to make further options addition simpler. We add use-copy-range with default=true, and we'll change the default in further patch, after moving backup to use block-copy. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210116214705.822267-2-vsementsov@virtuozzo.com> [mreitz: s/5\.2/6.0/] Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block: apply COR-filter to block-stream jobsAndrey Shinkevich
This patch completes the series with the COR-filter applied to block-stream operations. Adding the filter makes it possible in future implement discarding copied regions in backing files during the block-stream job, to reduce the disk overuse (we need control on permissions). Also, the filter now is smart enough to do copy-on-read with specified base, so we have benefit on guest reads even when doing block-stream of the part of the backing chain. Several iotests are slightly modified due to filter insertion. Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201216061703.70908-14-vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block/stream: add s->target_bsVladimir Sementsov-Ogievskiy
Add a direct link to target bs for convenience and to simplify following commit which will insert COR filter above target bs. This is a part of original commit written by Andrey. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20201216061703.70908-13-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26qapi: block-stream: add "bottom" argumentVladimir Sementsov-Ogievskiy
The code already don't freeze base node and we try to make it prepared for the situation when base node is changed during the operation. In other words, block-stream doesn't own base node. Let's introduce a new interface which should replace the current one, which will in better relations with the code. Specifying bottom node instead of base, and requiring it to be non-filter gives us the following benefits: - drop difference between above_base and base_overlay, which will be renamed to just bottom, when old interface dropped - clean way to work with parallel streams/commits on the same backing chain, which otherwise become a problem when we introduce a filter for stream job - cleaner interface. Nobody will surprised the fact that base node may disappear during block-stream, when there is no word about "base" in the interface. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201216061703.70908-11-vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26stream: rework backing-file changingAndrey Shinkevich
Stream in stream_prepare calls bdrv_change_backing_file() to change backing-file in the metadata of bs. It may use either backing-file parameter given by user or just take filename of base on job start. Backing file format is determined by base on job finish. There are some problems with this design, we solve only two by this patch: 1. Consider scenario with backing-file unset. Current concept of stream supports changing of the base during the job (we don't freeze link to the base). So, we should not save base filename at job start, - let's determine name of the base on job finish. 2. Using direct base to determine filename and format is not very good: base node may be a filter, so its filename may be JSON, and format_name is not good for storing into qcow2 metadata as backing file format. - let's use unfiltered_base Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [vsementsov: change commit subject, change logic in stream_prepare] Message-Id: <20201216061703.70908-10-vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26copy-on-read: skip non-guest reads if no copy neededAndrey Shinkevich
If the flag BDRV_REQ_PREFETCH was set, skip idling read/write operations in COR-driver. It can be taken into account for the COR-algorithms optimization. That check is being made during the block stream job by the moment. Add the BDRV_REQ_PREFETCH flag to the supported_read_flags of the COR-filter. block: Modify the comment for the flag BDRV_REQ_PREFETCH as we are going to use it alone and pass it to the COR-filter driver for further processing. Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20201216061703.70908-9-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26block: include supported_read_flags into BDS structureAndrey Shinkevich
Add the new member supported_read_flags to the BlockDriverState structure. It will control the flags set for copy-on-read operations. Make the block generic layer evaluate supported read flags before they go to a block driver. Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [vsementsov: use assert instead of abort] Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20201216061703.70908-8-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26qapi: copy-on-read filter: add 'bottom' optionAndrey Shinkevich
Add an option to limit copy-on-read operations to specified sub-chain of backing-chain, to make copy-on-read filter useful for block-stream job. Suggested-by: Max Reitz <mreitz@redhat.com> Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [vsementsov: change subject, modified to freeze the chain, do some fixes] Message-Id: <20201216061703.70908-6-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26qapi: add filter-node-name to block-streamAndrey Shinkevich
Provide the possibility to pass the 'filter-node-name' parameter to the block-stream job as it is done for the commit block job. Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [vsementsov: comment indentation, s/Since: 5.2/Since: 6.0/] Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20201216061703.70908-5-vsementsov@virtuozzo.com> [mreitz: s/commit/stream/] Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26copy-on-read: add filter drop functionAndrey Shinkevich
Provide API for the COR-filter removal. Also, drop the filter child permissions for an inactive state when the filter node is being removed. To insert the filter, the block generic layer function bdrv_insert_node() can be used. The new function bdrv_cor_filter_drop() may be considered as an intermediate solution before the QEMU permission update system has overhauled. Then we are able to implement the API function bdrv_remove_node() on the block generic layer. Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20201216061703.70908-4-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-26copy-on-read: support preadv/pwritev_part functionsAndrey Shinkevich
Add support for the recently introduced functions bdrv_co_preadv_part() and bdrv_co_pwritev_part() to the COR-filter driver. Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20201216061703.70908-2-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2021-01-13Merge remote-tracking branch 'remotes/armbru/tags/pull-yank-2021-01-13' into ↵Peter Maydell
staging Yank patches patches for 2021-01-13 # gpg: Signature made Wed 13 Jan 2021 09:25:46 GMT # gpg: using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653 # gpg: issuer "armbru@redhat.com" # gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full] # gpg: aka "Markus Armbruster <armbru@pond.sub.org>" [full] # Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867 4E5F 3870 B400 EB91 8653 * remotes/armbru/tags/pull-yank-2021-01-13: tests/test-char.c: Wait for the chardev to connect in char_socket_client_dupid_test io: Document qmp oob suitability of qio_channel_shutdown and io_shutdown io/channel-tls.c: make qio_channel_tls_shutdown thread-safe migration: Add yank feature chardev/char-socket.c: Add yank feature block/nbd.c: Add yank feature Introduce yank feature Signed-off-by: Peter Maydell <peter.maydell@linaro.org>