block/copy-on-read.c - qemu - Git at Google

 /*
  * Copy-on-read filter block driver
  *
  * Copyright (c) 2018 Red Hat, Inc.
  *
  * Author:
  *   Max Reitz <mreitz@redhat.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 or
  * (at your option) version 3 of the License.
  *
  * 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 "block/block-io.h"
 #include "block/block_int.h"
 #include "qemu/module.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "block/copy-on-read.h"


 typedef struct BDRVStateCOR {
     BlockDriverState *bottom_bs;
     bool chain_frozen;
 } BDRVStateCOR;


 static int cor_open(BlockDriverState *bs, QDict *options, int flags,
                     Error **errp)
 {
     BlockDriverState *bottom_bs = NULL;
     BDRVStateCOR *state = bs->opaque;
     /* Find a bottom node name, if any */
     const char *bottom_node = qdict_get_try_str(options, "bottom");
     int ret;

     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
     if (ret < 0) {
         return ret;
     }

     bs->supported_read_flags = BDRV_REQ_PREFETCH;

     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
         (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);

     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
             bs->file->bs->supported_zero_flags);

     if (bottom_node) {
         bottom_bs = bdrv_find_node(bottom_node);
         if (!bottom_bs) {
             error_setg(errp, "Bottom node '%s' not found", bottom_node);
             qdict_del(options, "bottom");
             return -EINVAL;
         }
         qdict_del(options, "bottom");

         if (!bottom_bs->drv) {
             error_setg(errp, "Bottom node '%s' not opened", bottom_node);
             return -EINVAL;
         }

         if (bottom_bs->drv->is_filter) {
             error_setg(errp, "Bottom node '%s' is a filter", bottom_node);
             return -EINVAL;
         }

         if (bdrv_freeze_backing_chain(bs, bottom_bs, errp) < 0) {
             return -EINVAL;
         }
         state->chain_frozen = true;

         /*
          * We do freeze the chain, so it shouldn't be removed. Still, storing a
          * pointer worth bdrv_ref().
          */
         bdrv_ref(bottom_bs);
     }
     state->bottom_bs = bottom_bs;

     /*
      * We don't need to call bdrv_child_refresh_perms() now as the permissions
      * will be updated later when the filter node gets its parent.
      */

     return 0;
 }


 #define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
                           | BLK_PERM_WRITE \
                           | BLK_PERM_RESIZE)
 #define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)

 static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
                            BdrvChildRole role,
                            BlockReopenQueue *reopen_queue,
                            uint64_t perm, uint64_t shared,
                            uint64_t *nperm, uint64_t *nshared)
 {
     *nperm = perm & PERM_PASSTHROUGH;
     *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;

     /* We must not request write permissions for an inactive node, the child
      * cannot provide it. */
     if (!(bs->open_flags & BDRV_O_INACTIVE)) {
         *nperm |= BLK_PERM_WRITE_UNCHANGED;
     }
 }


 static int64_t coroutine_fn cor_co_getlength(BlockDriverState *bs)
 {
     return bdrv_co_getlength(bs->file->bs);
 }


 static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs,
                                            int64_t offset, int64_t bytes,
                                            QEMUIOVector *qiov,
                                            size_t qiov_offset,
                                            BdrvRequestFlags flags)
 {
     int64_t n;
     int local_flags;
     int ret;
     BDRVStateCOR *state = bs->opaque;

     if (!state->bottom_bs) {
         return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
                                    flags | BDRV_REQ_COPY_ON_READ);
     }

     while (bytes) {
         local_flags = flags;

         /* In case of failure, try to copy-on-read anyway */
         ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
         if (ret <= 0) {
             ret = bdrv_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
                                           state->bottom_bs, true, offset,
                                           n, &n);
             if (ret > 0 || ret < 0) {
                 local_flags |= BDRV_REQ_COPY_ON_READ;
             }
             /* Finish earlier if the end of a backing file has been reached */
             if (n == 0) {
                 break;
             }
         }

         /* Skip if neither read nor write are needed */
         if ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) !=
             BDRV_REQ_PREFETCH) {
             ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
                                       local_flags);
             if (ret < 0) {
                 return ret;
             }
         }

         offset += n;
         qiov_offset += n;
         bytes -= n;
     }

     return 0;
 }


 static int coroutine_fn cor_co_pwritev_part(BlockDriverState *bs,
                                             int64_t offset,
                                             int64_t bytes,
                                             QEMUIOVector *qiov,
                                             size_t qiov_offset,
                                             BdrvRequestFlags flags)
 {
     return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
                                 flags);
 }


 static int coroutine_fn cor_co_pwrite_zeroes(BlockDriverState *bs,
                                              int64_t offset, int64_t bytes,
                                              BdrvRequestFlags flags)
 {
     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 }


 static int coroutine_fn cor_co_pdiscard(BlockDriverState *bs,
                                         int64_t offset, int64_t bytes)
 {
     return bdrv_co_pdiscard(bs->file, offset, bytes);
 }


 static int coroutine_fn cor_co_pwritev_compressed(BlockDriverState *bs,
                                                   int64_t offset,
                                                   int64_t bytes,
                                                   QEMUIOVector *qiov)
 {
     return bdrv_co_pwritev(bs->file, offset, bytes, qiov,
                            BDRV_REQ_WRITE_COMPRESSED);
 }


 static void coroutine_fn cor_co_eject(BlockDriverState *bs, bool eject_flag)
 {
     bdrv_co_eject(bs->file->bs, eject_flag);
 }


 static void coroutine_fn cor_co_lock_medium(BlockDriverState *bs, bool locked)
 {
     bdrv_co_lock_medium(bs->file->bs, locked);
 }


 static void cor_close(BlockDriverState *bs)
 {
     BDRVStateCOR *s = bs->opaque;

     if (s->chain_frozen) {
         s->chain_frozen = false;
         bdrv_unfreeze_backing_chain(bs, s->bottom_bs);
     }

     bdrv_unref(s->bottom_bs);
 }


 static BlockDriver bdrv_copy_on_read = {
     .format_name                        = "copy-on-read",
     .instance_size                      = sizeof(BDRVStateCOR),

     .bdrv_open                          = cor_open,
     .bdrv_close                         = cor_close,
     .bdrv_child_perm                    = cor_child_perm,

     .bdrv_co_getlength                  = cor_co_getlength,

     .bdrv_co_preadv_part                = cor_co_preadv_part,
     .bdrv_co_pwritev_part               = cor_co_pwritev_part,
     .bdrv_co_pwrite_zeroes              = cor_co_pwrite_zeroes,
     .bdrv_co_pdiscard                   = cor_co_pdiscard,
     .bdrv_co_pwritev_compressed         = cor_co_pwritev_compressed,

     .bdrv_co_eject                      = cor_co_eject,
     .bdrv_co_lock_medium                = cor_co_lock_medium,

     .has_variable_length                = true,
     .is_filter                          = true,
 };


 void bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs)
 {
     BDRVStateCOR *s = cor_filter_bs->opaque;

     /* unfreeze, as otherwise bdrv_replace_node() will fail */
     if (s->chain_frozen) {
         s->chain_frozen = false;
         bdrv_unfreeze_backing_chain(cor_filter_bs, s->bottom_bs);
     }
     bdrv_drop_filter(cor_filter_bs, &error_abort);
     bdrv_unref(cor_filter_bs);
 }


 static void bdrv_copy_on_read_init(void)
 {
     bdrv_register(&bdrv_copy_on_read);
 }

 block_init(bdrv_copy_on_read_init);
	/*
	* Copy-on-read filter block driver
	*
	* Copyright (c) 2018 Red Hat, Inc.
	*
	* Author:
	* Max Reitz <mreitz@redhat.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 or
	* (at your option) version 3 of the License.
	*
	* 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 "block/block-io.h"
	#include "block/block_int.h"
	#include "qemu/module.h"
	#include "qapi/error.h"
	#include "qapi/qmp/qdict.h"
	#include "block/copy-on-read.h"


	typedef struct BDRVStateCOR {
	BlockDriverState *bottom_bs;
	bool chain_frozen;
	} BDRVStateCOR;


	static int cor_open(BlockDriverState bs, QDict options, int flags,
	Error **errp)
	{
	BlockDriverState *bottom_bs = NULL;
	BDRVStateCOR *state = bs->opaque;
	/* Find a bottom node name, if any */
	const char *bottom_node = qdict_get_try_str(options, "bottom");
	int ret;

	ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
	if (ret < 0) {
	return ret;
	}

	bs->supported_read_flags = BDRV_REQ_PREFETCH;

	bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED \|
	(BDRV_REQ_FUA & bs->file->bs->supported_write_flags);

	bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED \|
	((BDRV_REQ_FUA \| BDRV_REQ_MAY_UNMAP \| BDRV_REQ_NO_FALLBACK) &
	bs->file->bs->supported_zero_flags);

	if (bottom_node) {
	bottom_bs = bdrv_find_node(bottom_node);
	if (!bottom_bs) {
	error_setg(errp, "Bottom node '%s' not found", bottom_node);
	qdict_del(options, "bottom");
	return -EINVAL;
	}
	qdict_del(options, "bottom");

	if (!bottom_bs->drv) {
	error_setg(errp, "Bottom node '%s' not opened", bottom_node);
	return -EINVAL;
	}

	if (bottom_bs->drv->is_filter) {
	error_setg(errp, "Bottom node '%s' is a filter", bottom_node);
	return -EINVAL;
	}

	if (bdrv_freeze_backing_chain(bs, bottom_bs, errp) < 0) {
	return -EINVAL;
	}
	state->chain_frozen = true;

	/*
	* We do freeze the chain, so it shouldn't be removed. Still, storing a
	* pointer worth bdrv_ref().
	*/
	bdrv_ref(bottom_bs);
	}
	state->bottom_bs = bottom_bs;

	/*
	* We don't need to call bdrv_child_refresh_perms() now as the permissions
	* will be updated later when the filter node gets its parent.
	*/

	return 0;
	}


	#define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
	\| BLK_PERM_WRITE \
	\| BLK_PERM_RESIZE)
	#define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)

	static void cor_child_perm(BlockDriverState bs, BdrvChild c,
	BdrvChildRole role,
	BlockReopenQueue *reopen_queue,
	uint64_t perm, uint64_t shared,
	uint64_t nperm, uint64_t nshared)
	{
	*nperm = perm & PERM_PASSTHROUGH;
	*nshared = (shared & PERM_PASSTHROUGH) \| PERM_UNCHANGED;

	/* We must not request write permissions for an inactive node, the child
	* cannot provide it. */
	if (!(bs->open_flags & BDRV_O_INACTIVE)) {
	*nperm \|= BLK_PERM_WRITE_UNCHANGED;
	}
	}


	static int64_t coroutine_fn cor_co_getlength(BlockDriverState *bs)
	{
	return bdrv_co_getlength(bs->file->bs);
	}


	static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs,
	int64_t offset, int64_t bytes,
	QEMUIOVector *qiov,
	size_t qiov_offset,
	BdrvRequestFlags flags)
	{
	int64_t n;
	int local_flags;
	int ret;
	BDRVStateCOR *state = bs->opaque;

	if (!state->bottom_bs) {
	return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
	flags \| BDRV_REQ_COPY_ON_READ);
	}

	while (bytes) {
	local_flags = flags;

	/* In case of failure, try to copy-on-read anyway */
	ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
	if (ret <= 0) {
	ret = bdrv_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
	state->bottom_bs, true, offset,
	n, &n);
	if (ret > 0 \|\| ret < 0) {
	local_flags \|= BDRV_REQ_COPY_ON_READ;
	}
	/* Finish earlier if the end of a backing file has been reached */
	if (n == 0) {
	break;
	}
	}

	/* Skip if neither read nor write are needed */
	if ((local_flags & (BDRV_REQ_PREFETCH \| BDRV_REQ_COPY_ON_READ)) !=
	BDRV_REQ_PREFETCH) {
	ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
	local_flags);
	if (ret < 0) {
	return ret;
	}
	}

	offset += n;
	qiov_offset += n;
	bytes -= n;
	}

	return 0;
	}


	static int coroutine_fn cor_co_pwritev_part(BlockDriverState *bs,
	int64_t offset,
	int64_t bytes,
	QEMUIOVector *qiov,
	size_t qiov_offset,
	BdrvRequestFlags flags)
	{
	return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
	flags);
	}


	static int coroutine_fn cor_co_pwrite_zeroes(BlockDriverState *bs,
	int64_t offset, int64_t bytes,
	BdrvRequestFlags flags)
	{
	return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
	}


	static int coroutine_fn cor_co_pdiscard(BlockDriverState *bs,
	int64_t offset, int64_t bytes)
	{
	return bdrv_co_pdiscard(bs->file, offset, bytes);
	}


	static int coroutine_fn cor_co_pwritev_compressed(BlockDriverState *bs,
	int64_t offset,
	int64_t bytes,
	QEMUIOVector *qiov)
	{
	return bdrv_co_pwritev(bs->file, offset, bytes, qiov,
	BDRV_REQ_WRITE_COMPRESSED);
	}


	static void coroutine_fn cor_co_eject(BlockDriverState *bs, bool eject_flag)
	{
	bdrv_co_eject(bs->file->bs, eject_flag);
	}


	static void coroutine_fn cor_co_lock_medium(BlockDriverState *bs, bool locked)
	{
	bdrv_co_lock_medium(bs->file->bs, locked);
	}


	static void cor_close(BlockDriverState *bs)
	{
	BDRVStateCOR *s = bs->opaque;

	if (s->chain_frozen) {
	s->chain_frozen = false;
	bdrv_unfreeze_backing_chain(bs, s->bottom_bs);
	}

	bdrv_unref(s->bottom_bs);
	}


	static BlockDriver bdrv_copy_on_read = {
	.format_name = "copy-on-read",
	.instance_size = sizeof(BDRVStateCOR),

	.bdrv_open = cor_open,
	.bdrv_close = cor_close,
	.bdrv_child_perm = cor_child_perm,

	.bdrv_co_getlength = cor_co_getlength,

	.bdrv_co_preadv_part = cor_co_preadv_part,
	.bdrv_co_pwritev_part = cor_co_pwritev_part,
	.bdrv_co_pwrite_zeroes = cor_co_pwrite_zeroes,
	.bdrv_co_pdiscard = cor_co_pdiscard,
	.bdrv_co_pwritev_compressed = cor_co_pwritev_compressed,

	.bdrv_co_eject = cor_co_eject,
	.bdrv_co_lock_medium = cor_co_lock_medium,

	.has_variable_length = true,
	.is_filter = true,
	};


	void bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs)
	{
	BDRVStateCOR *s = cor_filter_bs->opaque;

	/* unfreeze, as otherwise bdrv_replace_node() will fail */
	if (s->chain_frozen) {
	s->chain_frozen = false;
	bdrv_unfreeze_backing_chain(cor_filter_bs, s->bottom_bs);
	}
	bdrv_drop_filter(cor_filter_bs, &error_abort);
	bdrv_unref(cor_filter_bs);
	}


	static void bdrv_copy_on_read_init(void)
	{
	bdrv_register(&bdrv_copy_on_read);
	}

	block_init(bdrv_copy_on_read_init);