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

[Ritchie, Stuart]

On 4/17/11 5:43 AM, "Avi Kivity" <address@hidden> wrote:

>On 04/16/2011 02:58 AM, Ritchie, Stuart wrote:
>> >
>> >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.
>>
>> Please correct me if I am wrong, but with ivshmem you must to manage
>>your
>> world within a single, fixed size region.  I appreciate the simplicity
>>of
>> mapping the whole region all in one go, but our requirements are a bit
>> different.  Even if you could pass multiple -device ivshmem instances,
>> it's still a fixed environment.  Right?
>>
>
>You could place a read-only filesystem (say iso9660) in the region and
>mount it; it will then appear as a complete filesystem.

We've thought about formatting the region as a ramdisk, but the block
layer shields mmap() from the storage, thus requiring a data copy into the
page-cache.  The great thing about ramfs/tmpfs is the data is used
in-place; we'd lose that when going with a ramdisk or other real
filesystem.

--Stuart


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