Re: Proposal to improve filesystem/block snapshot interaction

["Jörn Engel" <joern@logfs.org>]

On Tue, 30 October 2007 18:35:08 +0900, Dongjun Shin wrote:
> On 10/30/07, Greg Banks <gnb@sgi.com> wrote:
> >
> > BIO_HINT_RELEASE
> >     The bio's block extent is no longer in use by the filesystem
> >     and will not be read in the future.  Any storage used to back
> >     the extent may be released without any threat to filesystem
> >     or data integrity.
> 
> I'd like to second the proposal, but it would be more useful to bring the hint
> down to the physical devices.

Absolutely.  Logfs would love to have an erase operation for block
devices as well.  However the above doesn't quite match my needs,
because the blocks _will_ be read in the future.

There are two reasons for reading things back later.  The good one is to
determine whether the segment was erased or not.  Reads should return
either valid data or one of (all-0xff, all-0x00, -ESOMETHING).  Having
a dedicated error code would be best.

And getting the device erasesize would be useful as well, for obvious
reasons.

Jörn

-- 
When you close your hand, you own nothing. When you open it up, you
own the whole world.
-- Li Mu Bai in Tiger & Dragon
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