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Re: [Qemu-block] [Qemu-devel] [PATCH] block/fleecing-filter: new filter
From: |
John Snow |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH] block/fleecing-filter: new filter driver for fleecing |
Date: |
Fri, 29 Jun 2018 15:18:11 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 |
On 06/21/2018 11:48 AM, Vladimir Sementsov-Ogievskiy wrote:
> We need to synchronize backup job with reading from fleecing image
> like it was done in block/replication.c.
>
> Otherwise, the following situation is theoretically possible:
>
> 1. client start reading
> 2. client understand, that there is no corresponding cluster in
> fleecing image
> 3. client is going to read from backing file (i.e. active image)
> 4. guest writes to active image
> 5. this write is stopped by backup(sync=none) and cluster is copied to
> fleecing image
> 6. guest write continues...
> 7. and client reads _new_ (or partly new) date from active image
>
> So, this fleecing-filter should be above fleecing image, the whole
> picture of fleecing looks like this:
>
> +-------+ +------------+
> | | | |
> | guest | | NBD client +<------+
> | | | | |
> ++-----++ +------------+ |only read
> | ^ |
> | IO | |
> v | +-----+------+
> ++-----+---------+ | |
> | | | internal |
> | active image +----+ | NBD server |
> | | | | |
> +-+--------------+ |backup +-+----------+
> ^ |sync=none ^
> |backing | |only read
> | | |
> +-+--------------+ | +------+----------+
> | | | | |
> | fleecing image +<---+ | fleecing filter |
> | | | |
> +--------+-------+ +-----+-----------+
> ^ |
> | |
> +--------------------------+
> file
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
> qapi/block-core.json | 9 ++++---
> block/fleecing-filter.c | 72
> +++++++++++++++++++++++++++++++++++++++++++++++++
> block/Makefile.objs | 1 +
> 3 files changed, 79 insertions(+), 3 deletions(-)
> create mode 100644 block/fleecing-filter.c
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index dfaa050651..b21bc3b693 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2543,7 +2543,8 @@
> 'host_device', 'http', 'https', 'iscsi', 'luks', 'nbd', 'nfs',
> 'null-aio', 'null-co', 'nvme', 'parallels', 'qcow', 'qcow2',
> 'qed',
> 'quorum', 'raw', 'rbd', 'replication', 'sheepdog', 'ssh',
> - 'throttle', 'vdi', 'vhdx', 'vmdk', 'vpc', 'vvfat', 'vxhs' ] }
> + 'throttle', 'vdi', 'vhdx', 'vmdk', 'vpc', 'vvfat', 'vxhs',
> + 'fleecing-filter' ] }
>
> ##
> # @BlockdevOptionsFile:
> @@ -3607,7 +3608,8 @@
> 'vmdk': 'BlockdevOptionsGenericCOWFormat',
> 'vpc': 'BlockdevOptionsGenericFormat',
> 'vvfat': 'BlockdevOptionsVVFAT',
> - 'vxhs': 'BlockdevOptionsVxHS'
> + 'vxhs': 'BlockdevOptionsVxHS',
> + 'fleecing-filter': 'BlockdevOptionsGenericFormat'
> } }
>
> ##
> @@ -4135,7 +4137,8 @@
> 'vmdk': 'BlockdevCreateNotSupported',
> 'vpc': 'BlockdevCreateOptionsVpc',
> 'vvfat': 'BlockdevCreateNotSupported',
> - 'vxhs': 'BlockdevCreateNotSupported'
> + 'vxhs': 'BlockdevCreateNotSupported',
> + 'fleecing-filter': 'BlockdevCreateNotSupported'
> } }
>
> ##
> diff --git a/block/fleecing-filter.c b/block/fleecing-filter.c
> new file mode 100644
> index 0000000000..60bac9c0b4
> --- /dev/null
> +++ b/block/fleecing-filter.c
> @@ -0,0 +1,72 @@
> +#include "qemu/osdep.h"
> +#include "qemu-common.h"
> +#include "block/blockjob.h"
> +#include "block/block_int.h"
> +#include "block/block_backup.h"
> +
> +static int64_t fleecing_getlength(BlockDriverState *bs)
> +{
> + return bdrv_getlength(bs->file->bs);
> +}
> +
> +static coroutine_fn int fleecing_co_preadv(BlockDriverState *bs,
> + uint64_t offset, uint64_t bytes,
> + QEMUIOVector *qiov, int flags)
> +{
> + int ret;
> + BlockJob *job = bs->file->bs->backing->bs->job;
> + CowRequest req;
> +
> + backup_wait_for_overlapping_requests(job, offset, bytes);
> + backup_cow_request_begin(&req, job, offset, bytes);
> +
> + ret = bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
> +
> + backup_cow_request_end(&req);
> +
> + return ret;
> +}
> +
> +static coroutine_fn int fleecing_co_pwritev(BlockDriverState *bs,
> + uint64_t offset, uint64_t bytes,
> + QEMUIOVector *qiov, int flags)
> +{
> + return -EINVAL;
> +}
> +
> +static bool fleecing_recurse_is_first_non_filter(BlockDriverState *bs,
> + BlockDriverState *candidate)
> +{
> + return bdrv_recurse_is_first_non_filter(bs->file->bs, candidate);
> +}
> +
> +static int fleecing_open(BlockDriverState *bs, QDict *options,
> + int flags, Error **errp)
> +{
> + bs->file = bdrv_open_child(NULL, options, "file", bs, &child_file, false,
> + errp);
> +
> + return bs->file ? 0 : -EINVAL;
> +}
> +
> +BlockDriver bdrv_fleecing_filter = {
> + .format_name = "fleecing-filter",
> + .protocol_name = "fleecing-filter",
> + .instance_size = 0,
> +
> + .bdrv_open = fleecing_open,
> +
> + .bdrv_getlength = fleecing_getlength,
> + .bdrv_co_preadv = fleecing_co_preadv,
> + .bdrv_co_pwritev = fleecing_co_pwritev,
> +
> + .is_filter = true,
> + .bdrv_recurse_is_first_non_filter = fleecing_recurse_is_first_non_filter,
> +};
> +
> +static void bdrv_fleecing_init(void)
> +{
> + bdrv_register(&bdrv_fleecing_filter);
> +}
> +
> +block_init(bdrv_fleecing_init);
> diff --git a/block/Makefile.objs b/block/Makefile.objs
> index 899bfb5e2c..aa0a6dd971 100644
> --- a/block/Makefile.objs
> +++ b/block/Makefile.objs
> @@ -27,6 +27,7 @@ block-obj-y += write-threshold.o
> block-obj-y += backup.o
> block-obj-$(CONFIG_REPLICATION) += replication.o
> block-obj-y += throttle.o copy-on-read.o
> +block-obj-y += fleecing-filter.o
>
> block-obj-y += crypto.o
>
>
Dropping this one from review queue in favor of the fleecing discussion
on "[Qemu-devel] [PATCH v2 0/3] image fleecing"
--js