Xen users - May 2005 - O_DIRECT for file-backed dom-U devices?

Hi again

It struck me that dom-U and dom-0 might be inadvertantly caching the 
same data.

For example, if a dom-U device is backed by a dom-0 device, is there 
anything specifically stopping dom-0 from caching the underlying block 
device (I presume theres some block-device-level caching?).

Even worse, with dom-U device backed by a loop-back file, it seems that 
the same data could be cached in dom-U at the file level and block 
level, and then again in dom-0 (for the FS containing the loop-back 
file) at the file and block level.

Are loop-back files specifically opened with O_DIRECT or similar when 
mounted as loop-back to prevent this?

Or maybe I''m just confused.
Roland




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