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

[Max Reitz]

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 <mre...@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.


Thanks,

Max

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