bwlp/qemu.git/block/nbd.c, branch spice_video_codecs

block: add BDRV_REQ_REGISTERED_BUF request flag

2022-10-26T18:56:42+00:00

Block drivers may optimize I/O requests accessing buffers previously registered with bdrv_register_buf(). Checking whether all elements of a request's QEMUIOVector are within previously registered buffers is expensive, so we need a hint from the user to avoid costly checks. Add a BDRV_REQ_REGISTERED_BUF request flag to indicate that all QEMUIOVector elements in an I/O request are known to be within previously registered buffers. Always pass the flag through to driver read/write functions. There is little harm in passing the flag to a driver that does not use it. Passing the flag to drivers avoids changes across many block drivers. Filter drivers would need to explicitly support the flag and pass through to their children when the children support it. That's a lot of code changes and it's hard to remember to do that everywhere, leading to silent reduced performance when the flag is accidentally dropped. The only problematic scenario with the approach in this patch is when a driver passes the flag through to internal I/O requests that don't use the same I/O buffer. In that case the hint may be set when it should actually be clear. This is a rare case though so the risk is low. Some drivers have assert(!flags), which no longer works when BDRV_REQ_REGISTERED_BUF is passed in. These assertions aren't very useful anyway since the functions are called almost exclusively by bdrv_driver_preadv/pwritev() so if we get flags handling right there then the assertion is not needed. Signed-off-by: Stefan Hajnoczi Message-id: 20221013185908.1297568-7-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi

nbd: add missing coroutine_fn annotations

2022-10-07T10:11:40+00:00

Callers of coroutine_fn must be coroutine_fn themselves, or the call must be within "if (qemu_in_coroutine())". Apply coroutine_fn to functions where this holds. Reviewed-by: Alberto Faria Reviewed-by: Eric Blake Signed-off-by: Paolo Bonzini Message-Id: <20220922084924.201610-11-pbonzini@redhat.com> [kwolf: Fixed up coding style] Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf

block: use 'unsigned' for in_flight field on driver state

2022-06-29T07:57:02+00:00

This patch makes in_flight field 'unsigned' for BDRVNBDState and MirrorBlockJob. This matches the definition of this field on BDS and is generically correct - we should never get negative value here. Signed-off-by: Denis V. Lunev CC: John Snow CC: Vladimir Sementsov-Ogievskiy CC: Kevin Wolf CC: Hanna Reitz CC: Eric Blake Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Vladimir Sementsov-Ogievskiy

nbd: trace long NBD operations

2022-06-29T07:57:02+00:00

At the moment there are 2 sources of lengthy operations if configured: * open connection, which could retry inside and * reconnect of already opened connection These operations could be quite lengthy and cumbersome to catch thus it would be quite natural to add trace points for them. This patch is based on the original downstream work made by Vladimir. Signed-off-by: Denis V. Lunev CC: Eric Blake CC: Vladimir Sementsov-Ogievskiy CC: Kevin Wolf CC: Hanna Reitz CC: Paolo Bonzini Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Vladimir Sementsov-Ogievskiy

nbd: Drop dead code spotted by Coverity

2022-06-24T15:07:06+00:00

CID 1488362 points out that the second 'rc >= 0' check is now dead code. Reported-by: Peter Maydell Fixes: 172f5f1a40(nbd: remove peppering of nbd_client_connected) Signed-off-by: Eric Blake Message-Id: <20220516210519.76135-1-eblake@redhat.com> Reviewed-by: Peter Maydell Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Kevin Wolf

nbd: document what is protected by the CoMutexes

2022-04-26T18:16:42+00:00

Signed-off-by: Paolo Bonzini Message-Id: <20220414175756.671165-10-pbonzini@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Lukas Straub Signed-off-by: Eric Blake

nbd: take receive_mutex when reading requests[].receiving

2022-04-26T18:16:41+00:00

requests[].receiving is set by nbd_receive_replies() under the receive_mutex; Read it under the same mutex as well. Waking up receivers on errors happens after each reply finishes processing, in nbd_co_receive_one_chunk(). If there is no currently-active reply, there are two cases: * either there is no active request at all, in which case no element of request[] can have .receiving = true * or nbd_receive_replies() must be running and owns receive_mutex; in that case it will get back to nbd_co_receive_one_chunk() because the socket has been shutdown, and all waiting coroutines will wake up in turn. Signed-off-by: Paolo Bonzini Message-Id: <20220414175756.671165-9-pbonzini@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Lukas Straub Signed-off-by: Eric Blake

nbd: move s->state under requests_lock

2022-04-26T18:16:39+00:00

Remove the confusing, and most likely wrong, atomics. The only function that used to be somewhat in a hot path was nbd_client_connected(), but it is not anymore after the previous patches. The same logic is used both to check if a request had to be reissued and also in nbd_reconnecting_attempt(). The former cases are outside requests_lock, while nbd_reconnecting_attempt() does have the lock, therefore the two have been separated in the previous commit. nbd_client_will_reconnect() can simply take s->requests_lock, while nbd_reconnecting_attempt() can inline the access now that no complicated atomics are involved. Signed-off-by: Paolo Bonzini Message-Id: <20220414175756.671165-8-pbonzini@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Lukas Straub Signed-off-by: Eric Blake

nbd: code motion and function renaming

2022-04-26T18:16:38+00:00

Prepare for the next patch, so that the diff is less confusing. nbd_client_connecting is moved closer to the definition point. nbd_client_connecting_wait() is kept only for the reconnection logic; when it is used to check if a request has to be reissued, use the renamed function nbd_client_will_reconnect(). In the next patch, the two cases will have different locking requirements. Signed-off-by: Paolo Bonzini Message-Id: <20220414175756.671165-7-pbonzini@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Lukas Straub Signed-off-by: Eric Blake

nbd: use a QemuMutex to synchronize yanking, reconnection and coroutines

2022-04-26T18:16:37+00:00

The condition for waiting on the s->free_sema queue depends on both s->in_flight and s->state. The latter is currently using atomics, but this is quite dubious and probably wrong. Because s->state is written in the main thread too, for example by the yank callback, it cannot be protected by a CoMutex. Introduce a separate lock that can be used by nbd_co_send_request(); later on this lock will also be used for s->state. There will not be any contention on the lock unless there is a yank or reconnect, so this is not performance sensitive. Signed-off-by: Paolo Bonzini Message-Id: <20220414175756.671165-6-pbonzini@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Lukas Straub Signed-off-by: Eric Blake