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

[Max Reitz <mreitz@redhat.com>]

On 05.03.2014 21:20, Benoît Canet wrote:
> The Wednesday 05 Mar 2014 à 20:58:12 (+0100), Max Reitz wrote :
>> On 05.03.2014 17:04, Benoît Canet wrote:
>>> 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 ?
>> You're right, that'd be shorter. It's just that I'm so in the habit
>> of writing "ret = foo(); if (ret < 0) { return ret; / goto fail; }"
>> that I didn't notice. ;-)
>>
>>>> +}
>>>> +
>>>> +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.
>> I'll just rebase on top of Paolo's series then.
> It's a sugestion made by Paolo. I wrote the actual code.
> The series is :
> "[PATCH] Rewrite block filter snapshot authorization mechanism"

Okay, thank you again. :-)

Max

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