Re: [Qemu-devel] Para-virtualized ram-based filesystem?

[Anthony Liguori <anthony@codemonkey.ws>]

On 04/15/2011 04:09 PM, Ritchie, Stuart wrote:
> Hi all,
>
> Has anyone looked at implementing a para-virtualized ram-based filesystem
> for qemu?  Or any similar dynamic memory mapping techniques for running
> guests?
>
> What I had in mind would be a convenient, zero-copy mechanism for sharing
> dynamically allocated, memory mapped files between host and guests.
>
> The host provides a primary memory-mapped file system (ramfs, tmpfs,
> hugetlbfs, etc), and the guest kernel and qemu use this host fs to provide
> the illusion to guest applications that the filesystem is local.
>
> The guest kernel contains a new filesystem, say call it vramfs,
> implementing the various VFS handlers for a para-virt filesystem.  These
> handlers call out to qemu, which in turn emulates them by invoking the
> required host system calls.

You can do this with ivshmem today.  You give it a path to a shared 
memory file, and then there's a path in sysfs that you can mmap() in 
userspace in the guest.

Regards,

Anthony Liguori

> Handling mmap/munmap is tricky -- but this is where the magic is.  There
> does seem to be some qemu infrastructure to dynamically map memory into a
> running system, though it may be designed for different requirements
> (e.g., device memory).
>
> I currently have the resources to work on this and am looking forward to
> contributing my work back to the community.  I would appreciate any help
> or pointers on this effort.
>
> Cheers,
> --Stuart
>
>
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