Re: [Xen-devel] [PATCH] Blktap: Userspace file-based image support. (RFC)

["Andrew Warfield" <andrew.warfield@xxxxxxxxxxxx>]

> A very much like the idea of a userspace block device backend.  Have you
> considered what it would take to completely replace blkback with a
> userspace backend?  I'm also curious why you choose a character device
> to interact with the ring queue instead of just attaching to the ring
> queue directly in userspace.
Oops (again), missed answering your char device question.  We just use
a char device to pin up a region of virtual address space for each
disk as it's presented in userspace.  Anyone familiar with blkback
will recognise the technique.  In our case, the first page is a
request/response ring between tap driver and application, and the
remainder is a sparsely populated address space where data pages are
mapped as they fly through.  We signal down with ioctl()s, and up
using poll().

a.

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