[Qemu-devel] iSER transport name is not good

[Qemu-devel] iSER transport name is not good

[Charles Kelimod]

Hello,


I'm on the road of modifying libvirt to add iSER support, and I found qemu
is actually support that. But, the transport name is iSER, which should be
RDMA and there libvirt already defined it.

Best Regards,
Charles.

Re: [Qemu-devel] iSER transport name is not good

[Dr. David Alan Gilbert]

* Charles Kelimod (lichstor@gmail.com) wrote:
> Hello,
> 
> 
> I'm on the road of modifying libvirt to add iSER support, and I found qemu
> is actually support that. But, the transport name is iSER, which should be
> RDMA and there libvirt already defined it.
> 
> Best Regards,
> Charles.

Hi Charles,
  So this is iSCSI extensions for RDMA?  I've cc'd in the qemu iSCSI
maintainers.
  Can you just explain what you're seeing libvirt do and what you think
qemu is expecting it to do for iSER?

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Qemu-devel] iSER transport name is not good

[ronnie sahlberg]

David,

Yes, QEMU has supported iSER (iSCSI extensions for RDMA) via a
userspace library, libiscsi, since about a year.
Here is a nice presentation from the developer of iSER support :
https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjChpba3PnXAhXBKZQKHQa9DEYQFggpMAA&url=https%3A%2F%2Fwww.snia.org%2Fsites%2Fdefault%2Ffiles%2FSDC%2F2016%2Fpresentations%2Fstorage_networking%2FShterman-Grimberg_Greenberg_Performance%2520Implications%2520Libiscsi_%2520RDMA_V6.pdf&usg=AOvVaw3xyvdIciRKVprboN6rClTA

In QEMU, you use it the same way as you would use the userspace iSCSI
support which has been in QEMU for quite a long time.
The only difference is that instead of providing a
iscsi://<host>/<iqn>/<lun> you select iSER by specifying an url of the
form
iser://<host>/<iqn>/<lun>


I.e. the only difference is the protocol part of the URL. When QEMU
passes this URL to libiscsi, it allows the library to decide on
whether to use normal iSCSI or whether it should use iSER.

I think RDMA would be a less good name for this as RDMA is not only
used to transport iSCSI but is also used for NFS as well as SMB.



regards
ronnie sahlberg


On Fri, Dec 8, 2017 at 4:41 AM, Dr. David Alan Gilbert
<dgilbert@redhat.com> wrote:
> * Charles Kelimod (lichstor@gmail.com) wrote:
>> Hello,
>>
>>
>> I'm on the road of modifying libvirt to add iSER support, and I found qemu
>> is actually support that. But, the transport name is iSER, which should be
>> RDMA and there libvirt already defined it.
>>
>> Best Regards,
>> Charles.
>
> Hi Charles,
>   So this is iSCSI extensions for RDMA?  I've cc'd in the qemu iSCSI
> maintainers.
>   Can you just explain what you're seeing libvirt do and what you think
> qemu is expecting it to do for iSER?
>
> Dave
>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Qemu-devel] iSER transport name is not good

[Charles Kelimod]

Hi Dave and Sahlberg,

for this type of name:iser://<host>/<iqn>/<lun>, I completely agree with
you.
my issue is when I create an vm from libvirt, the qemu command line should
be:
-drive
file.driver=iser,file.portal=xx.xx.xx.xx:3260,file.target=iqn.xxx,file.lun=0,file.transport=iser

Actually "iser" is added by me in libvirt, which can work by a little
modification. But I think file.transport=rdma would be better, as I think
iser is protocol, and rdma is transport, and libvirt defined it, if I added
a new transport name (iser) in libvirt, it will be confusable.

Best Regards,
Charles.

On Fri, Dec 8, 2017 at 2:07 PM, ronnie sahlberg <ronniesahlberg@gmail.com>
wrote:

> David,
>
> Yes, QEMU has supported iSER (iSCSI extensions for RDMA) via a
> userspace library, libiscsi, since about a year.
> Here is a nice presentation from the developer of iSER support :
> https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=
> web&cd=1&cad=rja&uact=8&ved=0ahUKEwjChpba3PnXAhXBKZQKHQa9D
> EYQFggpMAA&url=https%3A%2F%2Fwww.snia.org%2Fsites%2Fdefault%2Ffiles%2FSDC%
> 2F2016%2Fpresentations%2Fstorage_networking%2FShterman-Grimberg_Greenberg_
> Performance%2520Implications%2520Libiscsi_%2520RDMA_V6.pdf&usg=
> AOvVaw3xyvdIciRKVprboN6rClTA
>
> In QEMU, you use it the same way as you would use the userspace iSCSI
> support which has been in QEMU for quite a long time.
> The only difference is that instead of providing a
> iscsi://<host>/<iqn>/<lun> you select iSER by specifying an url of the
> form
> iser://<host>/<iqn>/<lun>
>
>
> I.e. the only difference is the protocol part of the URL. When QEMU
> passes this URL to libiscsi, it allows the library to decide on
> whether to use normal iSCSI or whether it should use iSER.
>
> I think RDMA would be a less good name for this as RDMA is not only
> used to transport iSCSI but is also used for NFS as well as SMB.
>
>
>
> regards
> ronnie sahlberg
>
>
> On Fri, Dec 8, 2017 at 4:41 AM, Dr. David Alan Gilbert
> <dgilbert@redhat.com> wrote:
> > * Charles Kelimod (lichstor@gmail.com) wrote:
> >> Hello,
> >>
> >>
> >> I'm on the road of modifying libvirt to add iSER support, and I found
> qemu
> >> is actually support that. But, the transport name is iSER, which should
> be
> >> RDMA and there libvirt already defined it.
> >>
> >> Best Regards,
> >> Charles.
> >
> > Hi Charles,
> >   So this is iSCSI extensions for RDMA?  I've cc'd in the qemu iSCSI
> > maintainers.
> >   Can you just explain what you're seeing libvirt do and what you think
> > qemu is expecting it to do for iSER?
> >
> > Dave
> >
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>

Re: [Qemu-devel] iSER transport name is not good

[Dr. David Alan Gilbert]

* Charles Kelimod (lichstor@gmail.com) wrote:
> Hi Dave and Sahlberg,
> 
> for this type of name:iser://<host>/<iqn>/<lun>, I completely agree with
> you.
> my issue is when I create an vm from libvirt, the qemu command line should
> be:
> -drive
> file.driver=iser,file.portal=xx.xx.xx.xx:3260,file.target=iqn.xxx,file.lun=0,file.transport=iser
> 
> Actually "iser" is added by me in libvirt, which can work by a little
> modification. But I think file.transport=rdma would be better, as I think
> iser is protocol, and rdma is transport, and libvirt defined it, if I added
> a new transport name (iser) in libvirt, it will be confusable.

This isn't something I know much about, however:
   a) The transport name is already defined as 'iser' in qemu, so that's
what needs to be used; we can't change it because someone somewhere
might alreadybe using it.
   b) iSER is a standard name for this, so it won't be confusing to
     people used to dealing with iSCSI over RDMA
   c) You of course need to check on the libvirt lists how they want
     to expose the setting.

Dave

> Best Regards,
> Charles.
> 
> On Fri, Dec 8, 2017 at 2:07 PM, ronnie sahlberg <ronniesahlberg@gmail.com>
> wrote:
> 
> > David,
> >
> > Yes, QEMU has supported iSER (iSCSI extensions for RDMA) via a
> > userspace library, libiscsi, since about a year.
> > Here is a nice presentation from the developer of iSER support :
> > https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=
> > web&cd=1&cad=rja&uact=8&ved=0ahUKEwjChpba3PnXAhXBKZQKHQa9D
> > EYQFggpMAA&url=https%3A%2F%2Fwww.snia.org%2Fsites%2Fdefault%2Ffiles%2FSDC%
> > 2F2016%2Fpresentations%2Fstorage_networking%2FShterman-Grimberg_Greenberg_
> > Performance%2520Implications%2520Libiscsi_%2520RDMA_V6.pdf&usg=
> > AOvVaw3xyvdIciRKVprboN6rClTA
> >
> > In QEMU, you use it the same way as you would use the userspace iSCSI
> > support which has been in QEMU for quite a long time.
> > The only difference is that instead of providing a
> > iscsi://<host>/<iqn>/<lun> you select iSER by specifying an url of the
> > form
> > iser://<host>/<iqn>/<lun>
> >
> >
> > I.e. the only difference is the protocol part of the URL. When QEMU
> > passes this URL to libiscsi, it allows the library to decide on
> > whether to use normal iSCSI or whether it should use iSER.
> >
> > I think RDMA would be a less good name for this as RDMA is not only
> > used to transport iSCSI but is also used for NFS as well as SMB.
> >
> >
> >
> > regards
> > ronnie sahlberg
> >
> >
> > On Fri, Dec 8, 2017 at 4:41 AM, Dr. David Alan Gilbert
> > <dgilbert@redhat.com> wrote:
> > > * Charles Kelimod (lichstor@gmail.com) wrote:
> > >> Hello,
> > >>
> > >>
> > >> I'm on the road of modifying libvirt to add iSER support, and I found
> > qemu
> > >> is actually support that. But, the transport name is iSER, which should
> > be
> > >> RDMA and there libvirt already defined it.
> > >>
> > >> Best Regards,
> > >> Charles.
> > >
> > > Hi Charles,
> > >   So this is iSCSI extensions for RDMA?  I've cc'd in the qemu iSCSI
> > > maintainers.
> > >   Can you just explain what you're seeing libvirt do and what you think
> > > qemu is expecting it to do for iSER?
> > >
> > > Dave
> > >
> > > --
> > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> >
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: [Qemu-devel] iSER transport name is not good

[Daniel P. Berrange]

On Fri, Dec 08, 2017 at 03:27:27PM +0800, Charles Kelimod wrote:
> Hi Dave and Sahlberg,
> 
> for this type of name:iser://<host>/<iqn>/<lun>, I completely agree with
> you.
> my issue is when I create an vm from libvirt, the qemu command line should
> be:
> -drive
> file.driver=iser,file.portal=xx.xx.xx.xx:3260,file.target=iqn.xxx,file.lun=0,file.transport=iser
> 
> Actually "iser" is added by me in libvirt, which can work by a little
> modification. But I think file.transport=rdma would be better, as I think
> iser is protocol, and rdma is transport, and libvirt defined it, if I added
> a new transport name (iser) in libvirt, it will be confusable.

If libvirt already supports this, then we won't change it, as that just creates
needless backcompatibility problems. There's many cases where we have wierd or
undesirable names for things, but at a low level we just accept them and carry
on, as wierd names don't have any negative functional impact. At the higher
app user interface, it can be renamed as desired, since UI has no backcompat
problems, as long as the low level stays the same.


Regards,
Daniel
-- 
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