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

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

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"

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