block: introduce backup-top filter driver (7df7868b) · Commits · SUMMER2020 / students / proj-2021291

block/Makefile.objs

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		@@ -42,6 +42,7 @@ block-obj-y += block-copy.o
		block-obj-y += crypto.o

		block-obj-y += aio_task.o
		block-obj-y += backup-top.o

		common-obj-y += stream.o

block/backup-top.c

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		/*
		* backup-top filter driver
		*
		* The driver performs Copy-Before-Write (CBW) operation: it is injected above
		* some node, and before each write it copies _old_ data to the target node.
		*
		* Copyright (c) 2018-2019 Virtuozzo International GmbH.
		*
		* Author:
		* Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
		*
		* This program is free software; you can redistribute it and/or modify
		* it under the terms of the GNU General Public License as published by
		* the Free Software Foundation; either version 2 of the License, or
		* (at your option) any later version.
		*
		* This program is distributed in the hope that it will be useful,
		* but WITHOUT ANY WARRANTY; without even the implied warranty of
		* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
		* GNU General Public License for more details.
		*
		* You should have received a copy of the GNU General Public License
		* along with this program. If not, see <http://www.gnu.org/licenses/>.
		*/

		#include "qemu/osdep.h"

		#include "sysemu/block-backend.h"
		#include "qemu/cutils.h"
		#include "qapi/error.h"
		#include "block/block_int.h"
		#include "block/qdict.h"
		#include "block/block-copy.h"

		#include "block/backup-top.h"

		typedef struct BDRVBackupTopState {
		BlockCopyState *bcs;
		BdrvChild *target;
		bool active;
		} BDRVBackupTopState;

		static coroutine_fn int backup_top_co_preadv(
		BlockDriverState *bs, uint64_t offset, uint64_t bytes,
		QEMUIOVector *qiov, int flags)
		{
		return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
		}

		static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
		uint64_t bytes)
		{
		/*
		* Here we'd like to use block_copy(), but block-copy need to be moved to
		* use BdrvChildren to correctly use it in backup-top filter. It's a TODO.
		*/

		abort();
		}

		static int coroutine_fn backup_top_co_pdiscard(BlockDriverState *bs,
		int64_t offset, int bytes)
		{
		int ret = backup_top_cbw(bs, offset, bytes);
		if (ret < 0) {
		return ret;
		}

		return bdrv_co_pdiscard(bs->backing, offset, bytes);
		}

		static int coroutine_fn backup_top_co_pwrite_zeroes(BlockDriverState *bs,
		int64_t offset, int bytes, BdrvRequestFlags flags)
		{
		int ret = backup_top_cbw(bs, offset, bytes);
		if (ret < 0) {
		return ret;
		}

		return bdrv_co_pwrite_zeroes(bs->backing, offset, bytes, flags);
		}

		static coroutine_fn int backup_top_co_pwritev(BlockDriverState *bs,
		uint64_t offset,
		uint64_t bytes,
		QEMUIOVector *qiov, int flags)
		{
		if (!(flags & BDRV_REQ_WRITE_UNCHANGED)) {
		int ret = backup_top_cbw(bs, offset, bytes);
		if (ret < 0) {
		return ret;
		}
		}

		return bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
		}

		static int coroutine_fn backup_top_co_flush(BlockDriverState *bs)
		{
		if (!bs->backing) {
		return 0;
		}

		return bdrv_co_flush(bs->backing->bs);
		}

		static void backup_top_refresh_filename(BlockDriverState *bs)
		{
		if (bs->backing == NULL) {
		/*
		* we can be here after failed bdrv_attach_child in
		* bdrv_set_backing_hd
		*/
		return;
		}
		pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
		bs->backing->bs->filename);
		}

		static void backup_top_child_perm(BlockDriverState bs, BdrvChild c,
		const BdrvChildRole *role,
		BlockReopenQueue *reopen_queue,
		uint64_t perm, uint64_t shared,
		uint64_t nperm, uint64_t nshared)
		{
		BDRVBackupTopState *s = bs->opaque;

		if (!s->active) {
		/*
		* The filter node may be in process of bdrv_append(), which firstly do
		* bdrv_set_backing_hd() and then bdrv_replace_node(). This means that
		* we can't unshare BLK_PERM_WRITE during bdrv_append() operation. So,
		* let's require nothing during bdrv_append() and refresh permissions
		* after it (see bdrv_backup_top_append()).
		*/
		*nperm = 0;
		*nshared = BLK_PERM_ALL;
		return;
		}

		if (role == &child_file) {
		/*
		* Target child
		*
		* Share write to target (child_file), to not interfere
		* with guest writes to its disk which may be in target backing chain.
		*/
		*nshared = BLK_PERM_ALL;
		*nperm = BLK_PERM_WRITE;
		} else {
		/* Source child */
		bdrv_filter_default_perms(bs, c, role, reopen_queue, perm, shared,
		nperm, nshared);

		if (perm & BLK_PERM_WRITE) {
		nperm = nperm \| BLK_PERM_CONSISTENT_READ;
		}
		*nshared &= ~BLK_PERM_WRITE;
		}
		}

		BlockDriver bdrv_backup_top_filter = {
		.format_name = "backup-top",
		.instance_size = sizeof(BDRVBackupTopState),

		.bdrv_co_preadv = backup_top_co_preadv,
		.bdrv_co_pwritev = backup_top_co_pwritev,
		.bdrv_co_pwrite_zeroes = backup_top_co_pwrite_zeroes,
		.bdrv_co_pdiscard = backup_top_co_pdiscard,
		.bdrv_co_flush = backup_top_co_flush,

		.bdrv_co_block_status = bdrv_co_block_status_from_backing,

		.bdrv_refresh_filename = backup_top_refresh_filename,

		.bdrv_child_perm = backup_top_child_perm,

		.is_filter = true,
		};

		BlockDriverState bdrv_backup_top_append(BlockDriverState source,
		BlockDriverState *target,
		const char *filter_node_name,
		uint64_t cluster_size,
		BdrvRequestFlags write_flags,
		BlockCopyState **bcs,
		Error **errp)
		{
		Error *local_err = NULL;
		BDRVBackupTopState *state;
		BlockDriverState *top = bdrv_new_open_driver(&bdrv_backup_top_filter,
		filter_node_name,
		BDRV_O_RDWR, errp);

		if (!top) {
		return NULL;
		}

		top->total_sectors = source->total_sectors;
		top->opaque = state = g_new0(BDRVBackupTopState, 1);

		bdrv_ref(target);
		state->target = bdrv_attach_child(top, target, "target", &child_file, errp);
		if (!state->target) {
		bdrv_unref(target);
		bdrv_unref(top);
		return NULL;
		}

		bdrv_drained_begin(source);

		bdrv_ref(top);
		bdrv_append(top, source, &local_err);
		if (local_err) {
		error_prepend(&local_err, "Cannot append backup-top filter: ");
		goto append_failed;
		}

		/*
		* bdrv_append() finished successfully, now we can require permissions
		* we want.
		*/
		state->active = true;
		bdrv_child_refresh_perms(top, top->backing, &local_err);
		if (local_err) {
		error_prepend(&local_err,
		"Cannot set permissions for backup-top filter: ");
		goto failed_after_append;
		}

		/*
		* TODO: Create block-copy-state here (which will utilize @cluster_size and
		* @write_flags parameters which are unused now). For this, block-copy
		* should be refactored to use BdrvChildren.
		*/
		state->bcs = NULL;
		if (!state->bcs) {
		error_setg(&local_err, "Cannot create block-copy-state");
		goto failed_after_append;
		}
		*bcs = state->bcs;

		bdrv_drained_end(source);

		return top;

		failed_after_append:
		state->active = false;
		bdrv_backup_top_drop(top);

		append_failed:
		bdrv_drained_end(source);
		bdrv_unref_child(top, state->target);
		bdrv_unref(top);
		error_propagate(errp, local_err);

		return NULL;
		}

		void bdrv_backup_top_drop(BlockDriverState *bs)
		{
		BDRVBackupTopState *s = bs->opaque;
		AioContext *aio_context = bdrv_get_aio_context(bs);

		block_copy_state_free(s->bcs);

		aio_context_acquire(aio_context);

		bdrv_drained_begin(bs);

		s->active = false;
		bdrv_child_refresh_perms(bs, bs->backing, &error_abort);
		bdrv_replace_node(bs, backing_bs(bs), &error_abort);
		bdrv_set_backing_hd(bs, NULL, &error_abort);

		bdrv_drained_end(bs);

		bdrv_unref(bs);

		aio_context_release(aio_context);
		}

block/backup-top.h

0 → 100644

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Original line number	Diff line number	Diff line
		/*
		* backup-top filter driver
		*
		* The driver performs Copy-Before-Write (CBW) operation: it is injected above
		* some node, and before each write it copies _old_ data to the target node.
		*
		* Copyright (c) 2018-2019 Virtuozzo International GmbH.
		*
		* Author:
		* Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
		*
		* This program is free software; you can redistribute it and/or modify
		* it under the terms of the GNU General Public License as published by
		* the Free Software Foundation; either version 2 of the License, or
		* (at your option) any later version.
		*
		* This program is distributed in the hope that it will be useful,
		* but WITHOUT ANY WARRANTY; without even the implied warranty of
		* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
		* GNU General Public License for more details.
		*
		* You should have received a copy of the GNU General Public License
		* along with this program. If not, see <http://www.gnu.org/licenses/>.
		*/

		#ifndef BACKUP_TOP_H
		#define BACKUP_TOP_H

		#include "block/block_int.h"
		#include "block/block-copy.h"

		BlockDriverState bdrv_backup_top_append(BlockDriverState source,
		BlockDriverState *target,
		const char *filter_node_name,
		uint64_t cluster_size,
		BdrvRequestFlags write_flags,
		BlockCopyState **bcs,
		Error **errp);
		void bdrv_backup_top_drop(BlockDriverState *bs);

		#endif /* BACKUP_TOP_H */