Re: [Qemu-devel] [PATCH 2/2] qemu-ga: add guest-fstrim command

[Michael Roth]

On Fri, Jun 22, 2012 at 10:48:56AM -0700, Chris Wedgwood wrote:
> > FITRIM is a mounted filesystem feature to discard (or "trim") blocks which
> > are not in use by the filesystem. This is useful for solid-state drives
> > (SSDs) and thinly-provisioned storage.  Provide access to the feature
> > from the host so that filesystems can be trimmed periodically or before
> > migration.
> 
> Why can't we use the block layer for this?   AHCI (I think) already
> has support, others could be added some some coordination.

I'm not sure I understand, wouldn't the filesystem need to be involved
at some level? How can the block layer differentiate lazilly discarded data
blocks from ones that are still in use without the aid of the
filesystem?

> 
> That was existing operating systems with current filesystems will DTRT
> when needed.
>