MMC and reliable write - was: since when does ARM map the kernel memory in sections?
pavel at ucw.cz
Mon Jun 6 06:28:55 EDT 2011
> > So basically add a new REQ_ flag - something like REQ_SAFE, which
> > would ensure that data
> > on block storage is not corrupted due to interrupting this write (or
> > even, after the write, if the card does some optimizations). We
> > already have a flag that ensures corruptions don't occur
> > because of local-to-disk caches - REQ_FUA, so this would just thinking
> > about what effects REQ_FUA already has that's not considered. On a
> > (spinning) disk, I can't image that interrupting a REQ_FUA write would
> > cause data loss somewhere other than where data was written.
> > Then it would be as simple as a mount flag that would ensure all
> > (write) accesses are FUA accesses, to ensure desired behavior for
> > platforms where power could be cut at any moment.
> I think you're mixing up different concepts.
> On a spinning hard disk, _all_ writes don't cause data loss other than
> where data is written, rounded up to the sector (512 or 4096 bytes).
Yes, so on mmc there are two different problems:
* reliability of write itself (REL_WRITE solves that)
* reliability of data around write (there are for bits "controlling"
it in 4.4.1 MMC specs, unfortunately they are only writable by card
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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