bwlp/qemu.git/block/copy-before-write.c, branch spice_video_codecs

block: introduce bdrv_open_file_child() helper

2022-10-27T18:14:11+00:00

Almost all drivers call bdrv_open_child() similarly. Let's create a helper for this. The only not updated drivers that call bdrv_open_child() to set bs->file are raw-format and snapshot-access: raw-format sometimes want to have filtered child but don't set drv->is_filter to true. snapshot-access wants only DATA | PRIMARY Possibly we should implement drv->is_filter_func() handler, to consider raw-format as filter when it works as filter.. But it's another story. Note also, that we decrease assignments to bs->file in code: it helps us restrict modifying this field in further commit. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Message-Id: <20220726201134.924743-3-vsementsov@yandex-team.ru> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf

copy-before-write: add missing coroutine_fn annotations

2022-10-07T10:11:41+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 Signed-off-by: Paolo Bonzini Message-Id: <20220922084924.201610-16-pbonzini@redhat.com> [kwolf: Fixed up coding style] Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf

block/copy-before-write: implement cbw-timeout option

2022-06-29T07:56:12+00:00

In some scenarios, when copy-before-write operations lasts too long time, it's better to cancel it. Most useful would be to use the new option together with on-cbw-error=break-snapshot: this way if cbw operation takes too long time we'll just cancel backup process but do not disturb the guest too much. Note the tricky point of realization: we keep additional point in bs->in_flight during block_copy operation even if it's timed-out. Background "cancelled" block_copy operations will finish at some point and will want to access state. We should care to not free the state in .bdrv_close() earlier. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz [vsementsov: use bdrv_inc_in_flight()/bdrv_dec_in_flight() instead of direct manipulation on bs->in_flight] Signed-off-by: Vladimir Sementsov-Ogievskiy

block/block-copy: block_copy(): add timeout_ns parameter

2022-06-29T07:56:12+00:00

Add possibility to limit block_copy() call in time. To be used in the next commit. As timed-out block_copy() call will continue in background anyway (we can't immediately cancel IO operation), it's important also give user a possibility to pass a callback, to do some additional actions on block-copy call finish. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Signed-off-by: Vladimir Sementsov-Ogievskiy

block/copy-before-write: add on-cbw-error open parameter

2022-06-28T07:20:31+00:00

Currently, behavior on copy-before-write operation failure is simple: report error to the guest. Let's implement alternative behavior: break the whole copy-before-write process (and corresponding backup job or NBD client) but keep guest working. It's needed if we consider guest stability as more important. The realisation is simple: on copy-before-write failure we set s->snapshot_ret and continue guest operations. s->snapshot_ret being set will lead to all further snapshot API requests. Note that all in-flight snapshot-API requests may still success: we do wait for them on BREAK_SNAPSHOT-failure path in cbw_do_copy_before_write(). Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Signed-off-by: Vladimir Sementsov-Ogievskiy

block/copy-before-write: refactor option parsing

2022-06-28T07:20:31+00:00

We are going to add one more option of enum type. Let's refactor option parsing so that we can simply work with BlockdevOptionsCbw object. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Signed-off-by: Vladimir Sementsov-Ogievskiy

block: copy-before-write: realize snapshot-access API

2022-03-07T08:33:31+00:00

Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz

block/copy-before-write: add bitmap open parameter

2022-03-07T08:33:30+00:00

This brings "incremental" mode to copy-before-write filter: user can specify bitmap so that filter will copy only "dirty" areas. Signed-off-by: Vladimir Sementsov-Ogievskiy Message-Id: <20220303194349.2304213-5-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz

block/block-copy: block_copy_state_new(): add bitmap parameter

2022-03-07T08:33:30+00:00

This will be used in the following commit to bring "incremental" mode to copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Message-Id: <20220303194349.2304213-4-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz

block/block-copy: move copy_bitmap initialization to block_copy_state_new()

2022-03-07T08:33:30+00:00

We are going to complicate bitmap initialization in the further commit. And in future, backup job will be able to work without filter (when source is immutable), so we'll need same bitmap initialization in copy-before-write filter and in backup job. So, it's reasonable to do it in block-copy. Note that for now cbw_open() is the only caller of block_copy_state_new(). Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Hanna Reitz Message-Id: <20220303194349.2304213-2-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz