Re: [Qemu-devel] [PATCH v3 1/5] support nbd driver in blockdev-add

[Markus Armbruster]

Wen Congyang <address@hidden> writes:

> The NBD driver needs: filename, path or (host, port, exportname).
> It checks which key exists and decides use unix or inet socket.
> It doesn't recognize the key type, so we can't use union, and
> can't reuse InetSocketAddress.
>
> Signed-off-by: Wen Congyang <address@hidden>
> Signed-off-by: zhanghailiang <address@hidden>
> Signed-off-by: Gonglei <address@hidden>
> ---
>  qapi/block-core.json | 42 ++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 11134a8..e68a59f 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1376,12 +1376,14 @@
>  #
>  # @host_device, @host_cdrom: Since 2.1
>  #
> +# @nbd: Since 2.5
> +#
>  # Since: 2.0
>  ##
>  { 'enum': 'BlockdevDriver',
>    'data': [ 'archipelago', 'blkdebug', 'blkverify', 'bochs', 'cloop',
>              'dmg', 'file', 'ftp', 'ftps', 'host_cdrom', 'host_device',
> -            'http', 'https', 'null-aio', 'null-co', 'parallels',
> +            'http', 'https', 'nbd', 'null-aio', 'null-co', 'parallels',
>              'qcow', 'qcow2', 'qed', 'quorum', 'raw', 'tftp', 'vdi', 'vhdx',
>              'vmdk', 'vpc', 'vvfat' ] }
>  
> @@ -1797,6 +1799,42 @@
>              '*read-pattern': 'QuorumReadPattern' } }
>  
>  ##
> +# @BlockdevOptionsNBD
> +#
> +# Driver specific block device options for NBD
> +#
> +# @filename: #optional unix or inet path. The format is:
> +#            unix: nbd+unix:///export?socket=path or
> +#                  nbd:unix:path:exportname=export
> +#            inet: nbd[+tcp]://host[:port]/export or
> +#                  nbd:host[:port]:exportname=export
> +#
> +# @path: #optional filesystem path to use
> +#
> +# @host: #optional host part of the address
> +#
> +# @port: #optional port part of the address
> +#
> +# @ipv4: #optional whether to accept IPv4 addresses, default try both IPv4
> +#        and IPv6
> +#
> +# @ipv6: #optional whether to accept IPv6 addresses, default try both IPv4
> +#        and IPv6
> +#
> +# @export: #optional the NBD export name
> +#
> +# Since: 2.5
> +##
> +{ 'struct': 'BlockdevOptionsNBD',
> +  'data': { '*filename': 'str',
> +            '*path':     'str',
> +            '*host':     'str',
> +            '*port':     'str',
> +            '*ipv4':     'bool',
> +            '*ipv6':     'bool',
> +            '*export':   'str' } }
> +
> +##

I'm afraid this doesn't address Eric's review of your v2.

In v2, you had

    { 'struct': 'BlockdevOptionsNBD',
      'base': 'InetSocketAddress',
      'data': { '*export': 'str' } }

Eric observed that InetSocketAddress can represent a port range.  Since
NBD doesn't support a range, he suggested to have two types rather than
InetSocketAddress: one to represent a single port, and another one to
represent a port range.  He further suggested to make the single port
type a base type of the port range type.

Eric further observed that support for the nbd+unix transport was
missing, and suggested to have a union type combining the various
transports.

Instead of that, you simply replaced InetSocketAddress by a bunch of
optional arguments with (unspoken!) conditions, such as "either
filename, or path+host".  That's not how we want things done in the
schema.

If we decide we want types separate for single ports and port range, you
need those two types.  For either one, you need a union type combining
transports.  It already exists for port ranges: SocketAddress.  You need
to create the other.

We can then discuss names.  For me, InetSocketAddress and SocketAddress
strongly suggest single port.  I'd prefer naming the port range types
*AddressRange or something.

If we decide separate types for single port and port ranges aren't
worthwhile, you can simply use SocketAddress where your v2 used
InetSocketAddress.

Eric, how strongly do you feel about separating the two?

>  # @BlockdevOptions
>  #
>  # Options for creating a block device.
> @@ -1822,7 +1860,7 @@
>        'http':       'BlockdevOptionsFile',
>        'https':      'BlockdevOptionsFile',
>  # TODO iscsi: Wait for structured options
> -# TODO nbd: Should take InetSocketAddress for 'host'?
> +      'nbd':        'BlockdevOptionsNBD',
>  # TODO nfs: Wait for structured options
>        'null-aio':   'BlockdevOptionsNull',
>        'null-co':    'BlockdevOptionsNull',