Re: [Qemu-devel] [PATCH v3 1/1] block/gluster: add support for multiple gluster backup volfile servers

[Eric Blake]

On 09/21/2015 05:24 AM, Prasanna Kumar Kalever wrote:
> This patch adds a way to specify multiple backup volfile servers to the 
> gluster
> block backend of QEMU with tcp|rdma transport types and their port numbers.
> 

> 
> This patch gives a mechanism to provide all the server addresses which are in
> replica set, so in case server1 is down VM can still boot from any of the
> active servers.
> 
> This is equivalent to the backup-volfile-servers option supported by
> mount.glusterfs (FUSE way of mounting gluster volume)
> 
> This patch depends on a recent fix in libgfapi raised as part of this work:
> http://review.gluster.org/#/c/12114/ (not merged yet)
> 

It would be nice to get that merged before we take this in qemu.

> Credits: Sincere thanks to Kevin Wolf <address@hidden> and
> "Deepak C Shetty" <address@hidden> for inputs and all their support
> 

Up to here is good.

> v1:
> multiple server addresses but common port number and transport type
> pattern: URI syntax with query (?) delimitor
> syntax:
>     file=gluster[+transport-type]://server1:24007/testvol/a.img\
>          ?backup-volfile-servers=server2&backup-volfile-servers=server3

But the changelog information here should instead occur...


> 
> Signed-off-by: Prasanna Kumar Kalever <address@hidden>
> ---

...here, so that it is helpful to reviewers but doesn't clog qemu.git
history (a year from now, we won't care how many iterations a patch went
through, only what got committed).


> +++ b/qapi/block-core.json
> @@ -1382,7 +1382,7 @@
>    'data': [ 'archipelago', 'blkdebug', 'blkverify', 'bochs', 'cloop',
>              'dmg', 'file', 'ftp', 'ftps', 'host_cdrom', 'host_device',
>              'host_floppy', 'http', 'https', 'null-aio', 'null-co', 
> 'parallels',
> -            'qcow', 'qcow2', 'qed', 'quorum', 'raw', 'tftp', 'vdi', 'vhdx',
> +            'qcow', 'qcow2', 'qed', 'quorum', 'gluster', 'raw', 'tftp', 
> 'vdi', 'vhdx',
>              'vmdk', 'vpc', 'vvfat' ] }

Please keep this list sorted.  Also, missing documentation that
'gluster' was added in 2.5.

>  
>  ##
> @@ -1794,6 +1794,43 @@
>              '*read-pattern': 'QuorumReadPattern' } }
>  
>  ##
> +# @GlusterTuplePattern

Name is long. Something like 'GlusterHost' would be nicer.

> +#
> +# Gluster tuple pattern
> +#
> +# @transport:    #transport type used to connect to gluster management daemon
> +#                 it can be tcp|rdma (default 'tcp')
> +#
> +# @port:         port number on which glusterd is listening. (default 24007)

To have a default, the parameter needs to be optional ('*port').

> +#
> +# @server:       server address (hostname/ipv4/ipv6 addresses)
> +#
> +# Since: 2.4+

s/2.4+/2.5/ (there is no 2.4+ release; the release that this will appear
in is 2.5)

> +##
> +{ 'struct': 'GlusterTuplePattern',
> +  'data': { 'server': 'str',
> +            'transport': 'str',

Yuck. Please don't open-code this as a 'str', but instead define it as
an enum:

{ 'enum': 'GlusterTransport', 'data': [ 'tcp', 'rdma' ] }

> +            'port': 'str' } }

Should port be an integer instead of a string? I guess we already allow
named ports in other network-related interfaces, but it would still be
nice to have an 'alternate' type that allows both integer and string.

It would be nice if your documentation of the parameters occurred in the
same order as the parameters appear in the 'struct'.

> +
> +##
> +# @BlockdevOptionsGluster
> +#
> +# Driver specific block device options for Gluster
> +#
> +# @volname:      name of gluster volume where our VM image resides
> +#
> +# @image-path:   absolute path to image file in gluster volume
> +#
> +# @backup-volfile-servers: holds multiple tuples of {server, transport, port}
> +#
> +# Since: 2.4+

s/2.4+/2.5/

> +##
> +{ 'struct': 'BlockdevOptionsGluster',
> +  'data': { 'volname': 'str',
> +            'image-path': 'str',
> +            'backup-volfile-servers': [ 'GlusterTuplePattern' ] } }

Shouldn't this be simply 'volfile-servers', as you are including the
primary server in addition to the backup servers?

> +
> +##
>  # @BlockdevOptions
>  #
>  # Options for creating a block device.
> @@ -1814,6 +1851,7 @@
>        'ftp':        'BlockdevOptionsFile',
>        'ftps':       'BlockdevOptionsFile',
>  # TODO gluster: Wait for structured options
> +      'gluster':    'BlockdevOptionsGluster',
>        'host_cdrom': 'BlockdevOptionsFile',
>        'host_device':'BlockdevOptionsFile',
>        'host_floppy':'BlockdevOptionsFile',
> 

There's also work on the list to expose NBD in a structured fashion; I'm
a bit worried that the two proposals might need to be sharing some
common functionality, rather than independently inventing slightly
different syntax.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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