MMC and reliable write - was: since when does ARM map the kernel memory in sections?

Pavel Machek pavel at
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
  manufacturer AFAICS).
(cesky, pictures)

More information about the linux-arm-kernel mailing list