Re: [fstests PATCH v6 2/2] generic: add test for DAX MAP_SYNC support

[Eryu Guan <eguan@redhat.com>]

On Thu, Dec 07, 2017 at 04:19:50PM -0700, Ross Zwisler wrote:
> This test creates a file and writes to it via an mmap(), but never syncs
> via fsync/msync.  This process is tracked via dm-log-writes, then replayed.
> 
> If MAP_SYNC is working the dm-log-writes replay will show the test file
> with 1 MiB of on-media block allocations.  This is because each allocating
> page fault included an implicit metadata sync.  If MAP_SYNC isn't working
> (which you can test by removing the "-S" flag to xfs_io mmap) the file
> will be smaller or missing entirely.
> 
> Note that dm-log-writes doesn't track the data that we write via the
> mmap(), so we can't do any data integrity checking.  We can only verify
> that the metadata writes for the page faults happened.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> 
> ---
> 
> Changes since v5:
>  - Addressed Eryu's comments.  Thanks for the review.

Thanks for the explanation on the dm-log-writes dax support! I agree
that we should keep _require_log_writes_dax for now till dm-log-writes
gains full dax support. I added some comments about this above the
helper definition and queued the patchset for next fstests update. (Test
was re-numbered as generic/470, BTW.)

Thanks,
Eryu