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[0/2] Tristate moount option comatibility fixup

Message ID cover.1604948373.git.msuchanek@suse.de
Headers show
Series Tristate moount option comatibility fixup | expand

Message

Michal Suchánek Nov. 9, 2020, 7:10 p.m. UTC 
Hello,

after the tristate dax option change some applications fail to detect
pmem devices because the dax option no longer shows in mtab when device
is mounted with -o dax.

At first it might seem stupid to detect pmem by looking at the mount
options.

However, if the application actually wants a mount point properly
configured for dax rather than just backed by pmem I do not see any
other easy way.

Also this happens during early installtion steps when the mounted
filesystem is typically empty and you want to perform non-destructive
detection.

If there are better ways to detect dax enabled mount poins I want to
hear all about it. In the meantime we have legacy applications to
support.

It also makes sense that when you mount a device with -o dax it actually
shows dax in the mount options. Not doind so is confusing for humans as
well.

Thanks

Michal

Michal Suchanek (2):
  xfs: show the dax option in mount options.
  ext4: show the dax option in mount options

References: bsc#1178366

 fs/ext4/super.c    | 2 +-
 fs/xfs/xfs_super.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Comments

Theodore Ts'o Nov. 10, 2020, 2:14 p.m. UTC | #1 
On Mon, Nov 09, 2020 at 08:10:07PM +0100, Michal Suchanek wrote:
> Hello,
> 
> after the tristate dax option change some applications fail to detect
> pmem devices because the dax option no longer shows in mtab when device
> is mounted with -o dax.

Which applications?  Name them.

We *really* don't want to encourage applications to make decisions
only based on the mount options.  For example, it could be that the
application's files will have the S_DAX flag set.

It would be a real shame if we are actively encourage applications to
use a broken configuration mechanism which was only used as a hack
while DAX was in experimental status.

						- Ted
Christoph Hellwig Nov. 10, 2020, 6:35 p.m. UTC | #2 
s/moount/mount/