Re: [Qemu-devel] [PATCH 02/10] block/json: Add JSON protocol driver

["Benoît Canet" <benoit.canet@irqsave.net>]

The Monday 03 Mar 2014 à 16:28:45 (+0100), Max Reitz wrote :
> Add a JSON protocol driver which allows supplying block driver options
> through the filename rather than separately. Other than that, it is a
> pure passthrough driver which identifies itself as a filter.
> 
> This patch implements the functions bdrv_parse_filename(),
> bdrv_file_open(), bdrv_close(), bdrv_aio_readv(), bdrv_aio_writev(),
> bdrv_getlength(), bdrv_refresh_limits() and bdrv_get_info().
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/Makefile.objs |   2 +-
>  block/json.c        | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 137 insertions(+), 1 deletion(-)
>  create mode 100644 block/json.c
> 
> diff --git a/block/Makefile.objs b/block/Makefile.objs
> index fd88c03..d4b70f4 100644
> --- a/block/Makefile.objs
> +++ b/block/Makefile.objs
> @@ -5,7 +5,7 @@ block-obj-y += qed-check.o
>  block-obj-$(CONFIG_VHDX) += vhdx.o vhdx-endian.o vhdx-log.o
>  block-obj-$(CONFIG_QUORUM) += quorum.o
>  block-obj-y += parallels.o blkdebug.o blkverify.o
> -block-obj-y += snapshot.o qapi.o
> +block-obj-y += snapshot.o qapi.o json.o
>  block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
>  block-obj-$(CONFIG_POSIX) += raw-posix.o
>  block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
> diff --git a/block/json.c b/block/json.c
> new file mode 100644
> index 0000000..6d63cf6
> --- /dev/null
> +++ b/block/json.c
> @@ -0,0 +1,136 @@
> +/*
> + * JSON filename wrapper protocol driver
> + *
> + * Copyright (c) 2014 Red Hat Inc.
> + *
> + * 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-common.h"
> +#include "block/block_int.h"
> +#include "qapi/qmp/qdict.h"
> +#include "qapi/qmp/qjson.h"
> +
> +static void json_parse_filename(const char *filename, QDict *options,
> +                                Error **errp)
> +{
> +    QObject *file_options_obj;
> +    QDict *full_options;
> +
> +    if (!strstart(filename, "json:", &filename)) {
> +        error_setg(errp, "Unknown protocol prefix for JSON block driver");
> +        return;
> +    }
> +
> +    file_options_obj = qobject_from_json(filename);
> +    if (!file_options_obj) {
> +        error_setg(errp, "Could not parse the JSON options");
> +        return;
> +    }
> +
> +    if (qobject_type(file_options_obj) != QTYPE_QDICT) {
> +        qobject_decref(file_options_obj);
> +        error_setg(errp, "Invalid JSON object");
> +        return;
> +    }
> +
> +    full_options = qdict_new();
> +    qdict_put_obj(full_options, "x-options", file_options_obj);
> +    qdict_flatten(full_options);
> +
> +    qdict_join(options, full_options, true);
> +    assert(qdict_size(full_options) == 0);
> +    QDECREF(full_options);
> +}
> +
> +static int json_open(BlockDriverState *bs, QDict *options, int flags,
> +                     Error **errp)
> +{
> +    int ret;
> +
> +    assert(bs->file == NULL);
> +    ret = bdrv_open_image(&bs->file, NULL, options, "x-options", flags, false,
> +                          errp);


> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    return 0;
Why not ?
    return ret;
}

Do you plan to enrich this code path later ?


> +}
> +
> +static void json_close(BlockDriverState *bs)
> +{
> +}
> +
> +static BlockDriverAIOCB *json_aio_readv(BlockDriverState *bs,
> +                                        int64_t sector_num, QEMUIOVector *qiov,
> +                                        int nb_sectors,
> +                                        BlockDriverCompletionFunc *cb,
> +                                        void *opaque)
> +{
> +    return bdrv_aio_readv(bs->file, sector_num, qiov, nb_sectors, cb, opaque);
> +}
> +
> +static BlockDriverAIOCB *json_aio_writev(BlockDriverState *bs,
> +                                         int64_t sector_num, QEMUIOVector *qiov,
> +                                         int nb_sectors,
> +                                         BlockDriverCompletionFunc *cb,
> +                                         void *opaque)
> +{
> +    return bdrv_aio_writev(bs->file, sector_num, qiov, nb_sectors, cb, opaque);
> +}
> +
> +static int64_t json_getlength(BlockDriverState *bs)
> +{
> +    return bdrv_getlength(bs->file);
> +}
> +
> +static int json_refresh_limits(BlockDriverState *bs)
> +{
> +    bs->bl = bs->file->bl;
> +    return 0;
> +}
> +
> +static int json_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
> +{
> +    return bdrv_get_info(bs->file, bdi);
> +}
> +
> +static BlockDriver bdrv_json = {
> +    .format_name                = "json",
> +    .protocol_name              = "json",
> +    .instance_size              = 0,
> +
> +    .bdrv_parse_filename        = json_parse_filename,
> +    .bdrv_file_open             = json_open,
> +    .bdrv_close                 = json_close,
> +
> +    .bdrv_aio_readv             = json_aio_readv,
> +    .bdrv_aio_writev            = json_aio_writev,
> +
> +    .has_variable_length        = true,
> +    .bdrv_getlength             = json_getlength,
> +
> +    .bdrv_refresh_limits        = json_refresh_limits,
> +    .bdrv_get_info              = json_get_info,
> +
> +    .authorizations             = { true, true },

Paolo make rewrite the snapshot authorization code.
In the new version you need
    .is_filter = true;
    .bdrv_recurse_is_first_children = your_implementation;

I don't know when these patchset will be reviewed and merged so maybe this
version is correct.

> +};
> +
> +static void bdrv_json_init(void)
> +{
> +    bdrv_register(&bdrv_json);
> +}
> +
> +block_init(bdrv_json_init);
> -- 
> 1.9.0
> 
>