Re: [Qemu-devel] [PATCH 2/2] Add the blockdev-reopen and blockdev-migrate commands

[Kevin Wolf <kwolf@redhat.com>]

Am 24.02.2012 12:37, schrieb Federico Simoncelli:
> Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
> ---
>  block/blkmirror.c |    2 +-
>  blockdev.c        |  109 +++++++++++++++++++++++++++++++++++++++++++++++------
>  hmp-commands.hx   |   36 +++++++++++++++++
>  hmp.c             |   30 ++++++++++++++
>  hmp.h             |    2 +
>  qapi-schema.json  |   63 ++++++++++++++++++++++++++++++
>  6 files changed, 229 insertions(+), 13 deletions(-)
> 
> diff --git a/block/blkmirror.c b/block/blkmirror.c
> index 39927c8..49e3381 100644
> --- a/block/blkmirror.c
> +++ b/block/blkmirror.c
> @@ -81,7 +81,7 @@ static int blkmirror_open(BlockDriverState *bs, const char *filename, int flags)
>          bdrv_delete(m->bs[0]);
>          return -ENOMEM;
>      }
> -    ret = bdrv_open(m->bs[1], filename, flags, NULL);
> +    ret = bdrv_open(m->bs[1], filename, flags | BDRV_O_NO_BACKING, NULL);
>      if (ret < 0) {
>          bdrv_delete(m->bs[0]);
>          return ret;

Was this hunk meant to be in patch 1?

> diff --git a/blockdev.c b/blockdev.c
> index 2c132a3..1df2542 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -646,9 +646,8 @@ void do_commit(Monitor *mon, const QDict *qdict)
>      }
>  }
>  
> -void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
> -                                bool has_format, const char *format,
> -                                Error **errp)
> +static void change_blockdev_image(const char *device, const char *new_image_file,
> +                                  const char *format, bool create, Error **errp)
>  {
>      BlockDriverState *bs;
>      BlockDriver *drv, *old_drv, *proto_drv;
> @@ -671,7 +670,7 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
>      old_drv = bs->drv;
>      flags = bs->open_flags;
>  
> -    if (!has_format) {
> +    if (!format) {
>          format = "qcow2";
>      }
>  
> @@ -681,24 +680,26 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
>          return;
>      }
>  
> -    proto_drv = bdrv_find_protocol(snapshot_file);
> +    proto_drv = bdrv_find_protocol(new_image_file);
>      if (!proto_drv) {
>          error_set(errp, QERR_INVALID_BLOCK_FORMAT, format);
>          return;
>      }
>  
> -    ret = bdrv_img_create(snapshot_file, format, bs->filename,
> -                          bs->drv->format_name, NULL, -1, flags);
> -    if (ret) {
> -        error_set(errp, QERR_UNDEFINED_ERROR);
> -        return;
> +    if (create) {
> +        ret = bdrv_img_create(new_image_file, format, bs->filename,
> +                              bs->drv->format_name, NULL, -1, flags);
> +        if (ret) {
> +            error_set(errp, QERR_UNDEFINED_ERROR);
> +            return;
> +        }
>      }
>  
>      bdrv_drain_all();
>      bdrv_flush(bs);
>  
>      bdrv_close(bs);
> -    ret = bdrv_open(bs, snapshot_file, flags, drv);
> +    ret = bdrv_open(bs, new_image_file, flags, drv);
>      /*
>       * If reopening the image file we just created fails, fall back
>       * and try to re-open the original image. If that fails too, we
> @@ -709,11 +710,95 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
>          if (ret != 0) {
>              error_set(errp, QERR_OPEN_FILE_FAILED, old_filename);
>          } else {
> -            error_set(errp, QERR_OPEN_FILE_FAILED, snapshot_file);
> +            error_set(errp, QERR_OPEN_FILE_FAILED, new_image_file);
>          }
>      }
>  }
>  
> +void qmp_blockdev_reopen(const char *device, const char *new_image_file,
> +                         bool has_format, const char *format, Error **errp)
> +{
> +    change_blockdev_image(device, new_image_file,
> +                          has_format ? format : NULL, false, errp);
> +}
> +
> +void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
> +                                bool has_format, const char *format,
> +                                Error **errp)
> +{
> +    change_blockdev_image(device, snapshot_file,
> +                          has_format ? format : NULL, true, errp);
> +}
> +
> +void qmp_blockdev_migrate(const char *device, BlockMigrateOp mode,
> +                          const char *destination, bool has_new_image_file,
> +                          const char *new_image_file, Error **errp)
> +{
> +    BlockDriverState *bs;
> +    BlockDriver *drv;
> +    int i, j, escape;
> +    char filename[2048];
> +
> +    bs = bdrv_find(device);
> +    if (!bs) {
> +        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> +        return;
> +    }
> +    if (bdrv_in_use(bs)) {
> +        error_set(errp, QERR_DEVICE_IN_USE, device);
> +        return;
> +    }
> +
> +    if (mode == BLOCK_MIGRATE_OP_MIRROR) {

Move into a separate function?

> +        drv = bdrv_find_format("blkmirror");
> +        if (!drv) {
> +            error_set(errp, QERR_INVALID_BLOCK_FORMAT, "blkmirror");
> +            return;
> +        }
> +
> +        if (!has_new_image_file) {
> +            new_image_file = bs->filename;
> +        }
> +
> +        pstrcpy(filename, sizeof(filename), "blkmirror:");
> +        i = strlen("blkmirror:");
> +
> +        escape = 0;
> +        for (j = 0; j < strlen(new_image_file); j++) {
> + loop:
> +            if (!(i < sizeof(filename) - 2)) {
> +                error_set(errp, QERR_INVALID_PARAMETER_VALUE,
> +                          "new-image-file", "shorter filename");
> +                return;
> +            }
> +
> +            if (new_image_file[j] == ':' || new_image_file[j] == '\\') {

Markus suggested that using comma for the separator is better even
though it requires escaping. It would allow to parse the option string
with QemuOpts.

> +                if (!escape) {
> +                    filename[i++] = '\\', escape = 1;
> +                    goto loop;
> +                } else {
> +                    escape = 0;
> +                }
> +            }
> +
> +            filename[i++] = new_image_file[j];
> +        }

Looks like a string helper for qemu-option.c (it contains the parser, so
keeping the escaping nearby would make sense).

> +
> +        if (i + strlen(destination) + 2 > sizeof(filename)) {
> +            error_set(errp, QERR_INVALID_PARAMETER_VALUE,
> +                      "destination", "shorter filename");
> +            return;
> +        }
> +
> +        filename[i++] = ':';
> +        pstrcpy(filename + i, sizeof(filename) - i - 2, destination);
> +
> +        change_blockdev_image(device, filename, "blkmirror", false, errp);
> +    } else if (mode == BLOCK_MIGRATE_OP_STREAM) {
> +        error_set(errp, QERR_NOT_SUPPORTED);

Why even define it then?

> +    }
> +}
> +
>  static void eject_device(BlockDriverState *bs, int force, Error **errp)
>  {
>      if (bdrv_in_use(bs)) {
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 573b823..ccb1f62 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -886,6 +886,42 @@ Snapshot device, using snapshot file as target if provided
>  ETEXI
>  
>      {
> +        .name       = "blkdev_reopen",

NACK on the name. Let's reserve blkdev_*/blockdev_* for the proper API
(that we'll release with the qemu version that comes with Hurd 1.0).

drive_* would align well with the existing drive_add/del commands.

> +        .args_type  = "device:B,new-image-file:s?,format:s?",
> +        .params     = "device [new-image-file] [format]",
> +        .help       = "Assigns a new image file to a device.\n\t\t\t"
> +                      "The image will be opened using the format\n\t\t\t"
> +                      "specified or 'qcow2' by default.",
> +        .mhandler.cmd = hmp_blkdev_reopen,
> +    },
> +
> +STEXI
> +@item blkdev_reopen
> +@findex blkdev_reopen
> +Assigns a new image file to a device.
> +ETEXI
> +
> +    {
> +        .name       = "blkdev_migrate",
> +        .args_type  = "mirror:-m,device:B,destination:s,new-image-file:s?",
> +        .params     = "device mode destination [new-image-file]",
> +        .help       = "Migrates the device to a new destination.\n\t\t\t"
> +                      "The default migration method is 'stream',\n\t\t\t"
> +                      "the option -m is used to select 'mirror'\n\t\t\t"
> +                      "(currently the only method supported).\n\t\t\t"
> +                      "An optional existing image file that will\n\t\t\t"
> +                      "replace the current one in the device\n\t\t\t"
> +                      "can be specified.",
> +        .mhandler.cmd = hmp_blkdev_migrate,
> +    },
> +
> +STEXI
> +@item blkdev_migrate
> +@findex blkdev_migrate
> +Migrates the device to a new destination.
> +ETEXI
> +
> +    {
>          .name       = "drive_add",
>          .args_type  = "pci_addr:s,opts:s",
>          .params     = "[[<domain>:]<bus>:]<slot>\n"
> diff --git a/hmp.c b/hmp.c
> index 8ff8c94..b687b8f 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -701,6 +701,36 @@ void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict)
>      hmp_handle_error(mon, &errp);
>  }
>  
> +void hmp_blkdev_reopen(Monitor *mon, const QDict *qdict)
> +{
> +    const char *device = qdict_get_str(qdict, "device");
> +    const char *filename = qdict_get_str(qdict, "new-image-file");
> +    const char *format = qdict_get_try_str(qdict, "format");
> +    Error *errp = NULL;
> +
> +    qmp_blockdev_reopen(device, filename, !!format, format, &errp);
> +    hmp_handle_error(mon, &errp);
> +}
> +
> +void hmp_blkdev_migrate(Monitor *mon, const QDict *qdict)
> +{
> +    bool mirror = qdict_get_try_bool(qdict, "mirror", 0);
> +    const char *device = qdict_get_str(qdict, "device");
> +    const char *destination = qdict_get_str(qdict, "destination");
> +    const char *new_image_file = qdict_get_try_str(qdict, "new-image-file");
> +    BlockMigrateOp mode;
> +    Error *errp = NULL;
> +
> +    if (mirror)
> +        mode = BLOCK_MIGRATE_OP_MIRROR;
> +    else
> +        mode = BLOCK_MIGRATE_OP_STREAM;
> +
> +    qmp_blockdev_migrate(device, mode, destination,
> +                         !!new_image_file, new_image_file, &errp);
> +    hmp_handle_error(mon, &errp);
> +}
> +
>  void hmp_migrate_cancel(Monitor *mon, const QDict *qdict)
>  {
>      qmp_migrate_cancel(NULL);
> diff --git a/hmp.h b/hmp.h
> index 18eecbd..f4e802b 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -47,6 +47,8 @@ void hmp_block_passwd(Monitor *mon, const QDict *qdict);
>  void hmp_balloon(Monitor *mon, const QDict *qdict);
>  void hmp_block_resize(Monitor *mon, const QDict *qdict);
>  void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict);
> +void hmp_blkdev_reopen(Monitor *mon, const QDict *qdict);
> +void hmp_blkdev_migrate(Monitor *mon, const QDict *qdict);
>  void hmp_migrate_cancel(Monitor *mon, const QDict *qdict);
>  void hmp_migrate_set_downtime(Monitor *mon, const QDict *qdict);
>  void hmp_migrate_set_speed(Monitor *mon, const QDict *qdict);
> diff --git a/qapi-schema.json b/qapi-schema.json
> index d02ee86..c86796a 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1136,6 +1136,69 @@
>    'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str' } }
>  
>  ##
> +# @blockdev-reopen
> +#
> +# Assigns a new image file to a device.
> +#
> +# @device: the name of the device for which we are chainging the image file.
> +#
> +# @new-image-file: the target of the new image. If the file doesn't exists the
> +#                  command will fail.
> +#
> +# @format: #optional the format of the new image, default is 'qcow2'.
> +#
> +# Returns: nothing on success
> +#          If @device is not a valid block device, DeviceNotFound
> +#          If @new-image-file can't be opened, OpenFileFailed
> +#          If @format is invalid, InvalidBlockFormat
> +#
> +# Since 1.1
> +##
> +
> +{ 'command': 'blockdev-reopen',
> +  'data': { 'device': 'str', 'new-image-file': 'str', '*format': 'str' } }

Same consideration on the name.

Also I think we should immediately mark the command as deprecated (I
think there is precedence for it, though I can't remember which command
it was). This is not an interface we'll want to keep long term.

Kevin