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RE: [Xen-devel] VBD extents
- To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx
- From: Eric Tessler <maiden1134@xxxxxxxxx>
- Date: Wed, 19 Jan 2005 14:53:40 -0800 (PST)
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So in XEN 2.0 is VBD grow/shrink used? I searched through the source code and could not find anyone who is generating these messages to blkback. From my understanding, blkback needs the VBD extent info to generate the I/O requests to the real disk device driver (the physical disk on domain 0). If indeed these messages will eventually be removed, i take it XEND will need to send a message to blkback identifying the disk device driver it should use for I/O (by supplying it a device ID like with the VBD extents).
Eric
Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx> wrote:
> Can anyone tell me what exactly the VBD extents are used for
> in the XEN back-end block device driver? It almost looks
> like each virtual disk is made up of multiple physical drives
> if I read the code correctly (for each VBD grow message
> received by blkback, it opens a device and retreives various
> info such as its size).
The extent stuff is left over from Xen 1.2, where we effectively had to
do our own version of LVM inside Xen. We'd like to give the code a
spring clean and do away with the grow/srink control messages
altogether. At the same time it would be sensible to add support for
multiple blk rings, and possibly the ability to 'tunnel' certain ioctls
e.g. eject CD.
Ian
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