Question: direct I/O for system volume

Question: direct I/O for system volume

[Jun Kamada]

Hi all,

I have a simple question about the device passthrough functionality,
that Xen 3.3 started to support. Does the functionality provide direct
I/O for "system volume" in guest domain? I suppose extension of many
components, such as guest firmware, will be needed. Somebody have a 
plan to do the extension?

Best regards,

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Jun Kamada

Re: Question: direct I/O for system volume

[Samuel Thibault]

Hello,

Jun Kamada, le Wed 27 Aug 2008 20:07:23 +0900, a écrit :
> Does the functionality provide direct I/O for "system volume" in guest
> domain?

What do you call "system volume"?

Samuel

Re: Question: direct I/O for system volume

[Jun Kamada]

Hi Samuel-san,

On Thu, 28 Aug 2008 09:59:08 +0100
Samuel Thibault <samuel.thibault@eu.citrix.com> wrote:
> Jun Kamada, le Wed 27 Aug 2008 20:07:23 +0900, a 馗rit :
> > Does the functionality provide direct I/O for "system volume" in guest
> > domain?
> 
> What do you call "system volume"?

Sorry, it means "boot disk". 

Guest software can directly see HBA(Host Bus Adapter) as a hardware 
by using the device passthrough functionality. However, current guest
BIOS doesn't have a capability to load and invoke expansion ROM stored 
in the HBA, I guess. As a result, the guest OS cannot boot up from a 
disk under the HBA.

#If my understanding was wrong, please point out.

I understand that this limitation does not come from the device
passthrough functionality, but probably from guest BIOS or the other
component.

Best regards,


-----
Jun Kamada

Re: Question: direct I/O for system volume

[Samuel Thibault]

Hello,

Jun Kamada, le Thu 28 Aug 2008 18:31:23 +0900, a écrit :
> On Thu, 28 Aug 2008 09:59:08 +0100
> Samuel Thibault <samuel.thibault@eu.citrix.com> wrote:
> > Jun Kamada, le Wed 27 Aug 2008 20:07:23 +0900, a 馗rit :
> > > Does the functionality provide direct I/O for "system volume" in guest
> > > domain?
> > 
> > What do you call "system volume"?
> 
> Sorry, it means "boot disk". 
> 
> Guest software can directly see HBA(Host Bus Adapter) as a hardware 
> by using the device passthrough functionality. However, current guest
> BIOS doesn't have a capability to load and invoke expansion ROM stored 
> in the HBA, I guess. As a result, the guest OS cannot boot up from a 
> disk under the HBA.

Ok, much more clear :)
You may want to have a look at Jean Guyader's work on VGA card
pass-through, which precisely requires mapping the expansion ROM into
the guest.  In other words, the tools to achieve it are there, I guess
you just need to assemble them.

Samuel

Re: Question: direct I/O for system volume

[Jun Kamada]

Hi Samuel-san,

Thank you for your helpful information. I will access the work.

Best regards,


On Thu, 28 Aug 2008 10:44:41 +0100
Samuel Thibault <samuel.thibault@eu.citrix.com> wrote:

> Hello,
> 
> Jun Kamada, le Thu 28 Aug 2008 18:31:23 +0900, a ecrit :
> > On Thu, 28 Aug 2008 09:59:08 +0100
> > Samuel Thibault <samuel.thibault@eu.citrix.com> wrote:
> > > Jun Kamada, le Wed 27 Aug 2008 20:07:23 +0900, a 馗rit :
> > > > Does the functionality provide direct I/O for "system volume" in guest
> > > > domain?
> > > 
> > > What do you call "system volume"?
> > 
> > Sorry, it means "boot disk". 
> > 
> > Guest software can directly see HBA(Host Bus Adapter) as a hardware 
> > by using the device passthrough functionality. However, current guest
> > BIOS doesn't have a capability to load and invoke expansion ROM stored 
> > in the HBA, I guess. As a result, the guest OS cannot boot up from a 
> > disk under the HBA.
> 
> Ok, much more clear :)
> You may want to have a look at Jean Guyader's work on VGA card
> pass-through, which precisely requires mapping the expansion ROM into
> the guest.  In other words, the tools to achieve it are there, I guess
> you just need to assemble them.
> 
> Samuel


-----
Jun Kamada