Mailinglist Archive: yast-devel (211 mails)

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Re: [yast-devel] High level notes about new storage API
On Fri, Oct 23, 2015 at 10:24:05AM +0200, Josef Reidinger wrote:
On Thu, 22 Oct 2015 17:04:35 +0200
Arvin Schnell <aschnell@xxxxxxxx> wrote:

On Thu, Oct 22, 2015 at 08:59:52AM +0200, Josef Reidinger wrote:

You can mount a device at several mount-points. With btrfs this
is even standard, see
https://github.com/openSUSE/libstorage/blob/master/doc/status-current-code.md.

Yes, I know that device can have multiple mountpoints, but here is
logic reverse. It said that one mount point can have multiple
devices ( or filesystem like used here ) which is at least for
common usage without overlapper layered mount points not possible.

It is possible, although likely stupid:

cat /proc/mounts
[...]
/dev/mapper/system-abuild /mnt ext4 rw,relatime,commit=600 0 0
/dev/mapper/system-giant--xfs /mnt xfs
rw,relatime,attr2,inode64,noquota 0 0

So the API must be able to handle the situation. Or do you prefer
an exception during probing?

I think it is two different things.

1) probing should handle such situation

2) common query should return only later as first one is overlaped, of
course there can be specialized call to manipulate mount points knowing
also about overlap or knowing that removing first mount point return to
game previous one

Currently the ordering does not define that information.

I had a different use-case in mind: If you want to delete
/dev/mapper/system-abuild you first have to unmount it. Since
umount(2) only supports unmounting the topmost filesystem you
also have to unmount /dev/mapper/system-giant--xfs. You have to
present that to the user. So you need all filesystems mounted at
that place.

I do not look at API from probe POV, but from library user POV, so I
query what device content is visible under /mnt, which answer is only
second one.

In general you have to look at the API from both sides. After all
the API has to represent the system and not some theoretic
concept.

Regards,
Arvin

--
Arvin Schnell, <aschnell@xxxxxxxx>
Senior Software Engineer, Research & Development
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
Maxfeldstraße 5
90409 Nürnberg
Germany
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