On Thu, 2014-07-17 at 13:59 -0700, Andrew Morton wrote:
> On Thu, 17 Jul 2014 19:32:42 +0300 Sougata Santra <sougata@xxxxxxxxxx> wrote:
>
> > hfsplus_sync_fs always updates volume header information to disk with every
> > sync. This causes problem for systems trying to monitor disk activity to
> > switch them to low power state.
>
> Please fully describe these "problems"? I'm guessing that the fs will
> write the volume header even if it didn't change, so a sync operation
> against a completely clean fs still performs a physical write. But I'd
> prefer not to have to guess!
Absolutely sorry, I assumed it was made clear from the cover letter.
Yes, as you described, the problem is that HFS+ syncs volume header
even if it did not change with every sync operation. Also, I have
done some additional changes because I was modifying hfsplus_sync_fs,
and the problems were relevant, and I thought they should be addressed
in the same patch. Please find them below:
Please Note:
-----------
1) hfsplus_sync_volume_header() is added to call from mount/unmount
sequence, since we just want to write the dirty/clean state to disk.
For unmount, hfsplus_sync_fs is already called from sync_filesystem().
For mount, it gets called from delayed_sync_fs().
2) Also, there was a error in error propagation. It it also fixed in
this patch.
-->snip<--
if (!error)
error2 = error;
-->snap<--
3) The disk is only flushed if there was no error. Previously it was
always flushed without checking the error.
Thanks a lot,
Best regards,
Sougata
>
> > Also hfsplus_sync_fs is explicitly called
> > from mount/unmount, which is unnecessary. During mount/unmount we only want
> > to set/clear volume dirty sate.
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