block/gluster: add support for multiple gluster servers

block/gluster: add support for multiple gluster servers

This patch adds a way to specify multiple volfile servers to the gluster
block backend of QEMU with tcp|rdma transport types and their port numbers.

Problem:

Currently VM Image on gluster volume is specified like this:

file=gluster[+tcp]://host[:port]/testvol/a.img

Say we have three hosts in a trusted pool with replica 3 volume in action.
When the host mentioned in the command above goes down for some reason,
the other two hosts are still available. But there's currently no way
to tell QEMU about them.

Solution:

New way of specifying VM Image on gluster volume with volfile servers:
(We still support old syntax to maintain backward compatibility)

Basic command line syntax looks like:

Pattern I:
 -drive driver=gluster,
        volume=testvol,path=/path/a.raw,[debug=N,]
        server.0.type=tcp,
        server.0.host=1.2.3.4,
        server.0.port=24007,
        server.1.type=unix,
        server.1.socket=/path/socketfile

Pattern II:
 'json:{"driver":"qcow2","file":{"driver":"gluster",
       "volume":"testvol","path":"/path/a.qcow2",["debug":N,]
       "server":[{hostinfo_1}, ...{hostinfo_N}]}}'

   driver      => 'gluster' (protocol name)
   volume      => name of gluster volume where our VM image resides
   path        => absolute path of image in gluster volume
  [debug]      => libgfapi loglevel [(0 - 9) default 4 -> Error]

  {hostinfo}   => {{type:"tcp",host:"1.2.3.4"[,port=24007]},
                   {type:"unix",socket:"/path/sockfile"}}

   type        => transport type used to connect to gluster management daemon,
                  it can be tcp|unix
   host        => host address (hostname/ipv4/ipv6 addresses/socket path)
   port        => port number on which glusterd is listening.
   socket      => path to socket file

Examples:
1.
 -drive driver=qcow2,file.driver=gluster,
        file.volume=testvol,file.path=/path/a.qcow2,file.debug=9,
        file.server.0.type=tcp,
        file.server.0.host=1.2.3.4,
        file.server.0.port=24007,
        file.server.1.type=unix,
        file.server.1.socket=/var/run/glusterd.socket
2.
  'json:{"driver":"qcow2","file":{"driver":"gluster","volume":"testvol",
         "path":"/path/a.qcow2","debug":9,"server":
         [{"type":"tcp","host":"1.2.3.4","port":"24007"},
          {"type":"unix","socket":"/var/run/glusterd.socket"}
         ]}}'

This patch gives a mechanism to provide all the server addresses, which are in
replica set, so in case host1 is down VM can still boot from any of the
active hosts.

This is equivalent to the backup-volfile-servers option supported by
mount.glusterfs (FUSE way of mounting gluster volume)

credits: sincere thanks to all the supporters

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1468947453-5433-6-git-send-email-prasanna.kalever@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>