RE: [Xen-users] ioemu in config file and O_DIRECT option

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> trilok nuwal
> Sent: 07 March 2007 15:11
> To: Xen list
> Subject: [Xen-users] ioemu in config file and O_DIRECT option
> 
> In config file,  'type=ioemu' is added with vif .  Does it 
> make the difference if we don't add.
> Because i did not notice any difference in para as well as 
> full virtulization.
> Same as in case of exporting the disk to Guest dom. Is it 
> just a placeholder or else ?

I think it's "not important" - I'm not entirely sure if there's
historical reasons for it or if it's a "may be needed in the future" (or
both). 
> 
> Second thing, I am running RHEL3 as a HVM DomU on xen-3.0.4.  
> Every thing works fine, but i had a problem to write a file 
> opened with O_DIRECT  option. 
> Does it supports all file IO options ( O_DIRECT etc. )  that 
> RHEL3 supports as normal or does it depends on the drivers, 
> that only for a set of drivers is supports 
> all IO options or something we have to configure in DomU.

In HVM mode, you should be able to do exactly the same things as if
you're running on hardware. I doubt that the basic IDE driver wouldn't
support O_DIRECT. However, O_DIRECT will only work "locally", so if
you're expecting your writes to be unbuffered all the way to the
hardware, that's not going to happen, because Xen gets in the way. 

--
Mats
> 
> Thanks,
> --Trilok 
> 
> 



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