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Re: [Qemu-devel] [PATCH 1/1] Migration: libvirt live migration over RDMA

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] [PATCH 1/1] Migration: libvirt live migration over RDMA of ipv6 addr failed
Date: Tue, 24 Jan 2017 17:36:19 +0000
User-agent: Mutt/1.7.1 (2016-10-04)

On Tue, Jan 24, 2017 at 09:44:33AM -0600, David Dai wrote:
> Using libvirt to do live migration over RDMA via ip v6 address failed. 
> For example:
> # virsh migrate  --live --migrateuri rdma://[deba::2222]:49152  \
>               rhel73_host1_guest1 qemu+ssh://[deba::2222]/system --verbose
> address@hidden::2222's password:
> error: internal error: unable to execute QEMU command 'migrate': RDMA ERROR:  
>                   could not rdma_getaddrinfo address deba
> As we can see, the ip v6 address used by rdma_getaddrinfo() has only "deba" 
> part. It should be "deba::2222".
> 1) According to rfc 3986, a literal ip v6 address should be enclosed 
> in '[' and ']'.
> When using virsh command to do live migration via ip v6 addresss, user
> will input the ip v6 address with brackets (i.e. rdma://[deba::2222]:49152).
> libvirt will parse command line option by calling virURIParse(). 
> Inside it calls virStringStripIPv6Brackets() to strip off the brackets.
> The uri passed in to virURIParse()  is:
>    "uri = rdma://[deba::2222]:49152"
> Inside virURIParse() routine, it will strip off the bracket '[' and ']' if
> it's ip v6 address. Then save the ip v6 address in this format "deba::2222" 
> in the virURI->server field, and to be passed to qemu.
> 2) At the beginning of migration, in qemu's qemu_rdma_data_init(host_port) 
> routine, it calls inet_parse(host_port) routine to parse the ip v6 address 
> and 
> port string obtained from libvirt.
> The input string host_port passed to qemu_rdma_data_init() can be:
>     "hostname:port", or
>     "ipv4address:port", or
>     "[ipv6address]:port" (i.e "[deba::2222]:49152"), or
>     "ipv6address:port" (i.e "deba::2222:49152").
> Existing qemu api inet_parse() can handle the above first 3 cases properly,  
> but didn't handle the last case ("ipv6address:port") correctly.
> In this live migration over rdma via ip v6 address case, the server ip v6 
> address obtained from libvirt doesn't contain the brackets '[' and ']' 
> (i.e. "deba::2222:49152"). It caused inet_parse() to parse only "deba" part, 
> and stopped at the 1st colon ':'. As the result, the subsequent 
> rdma_getaddrinfo() with ip address "deba" will fail.
> If we don't strip off brackets '[' and ']' for an ip v6 address in libvirt's 
> virURIParse(), it will cause libvirt ipv6 ssh authentication failure.
> If using libvirt to do live migration over TCP via ip v6 address:
> # virsh migrate  --live --migrateuri tcp://[deba::2222]:49152  \
>               rhel73_host1_guest1 qemu+ssh://[deba::2222]/system --verbose
> It works fine.
> In migrateuri of tcp case, libvirt will call virNetSocketNewConnectTCP()
> directly to connect to remote "deba::2222:49152" after it strips off
> the bracket '[' and ']' for an ip v6 address. 
> On qemu side, fd_start_outgoing_migration() will be called to do migration.
> It doesn't call inet_parse(). So we don't see issue in tcp case.
> Solution:
> I choose to fix the code in qemu's inet_parse() routine to parse the
> ip v6 addresss w/o brackets properly (i.e. "deba::2222:49152" format).

That is not right - "deba::222:49152" is *not* a valid address. It
is mandatory to use [] when providing a numeric IPv6 address. So
there's nothing broken in QEMU here - libvirt needs fixing to pass
correct data to QEMU

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