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Re: [Libguestfs] [PATCHv4 0/2] Introduce vfs_minimum_size API to get minimum filesystem size.

On Wed, Oct 21, 2015 at 03:44:28PM +0300, Maxim Perevedentsev wrote:
> On 10/20/2015 08:58 PM, Richard W.M. Jones wrote:
> >On Tue, Oct 20, 2015 at 08:56:25PM +0300, Maxim Perevedentsev wrote:
> >>I have an issue with btrfs:
> >>
> >>There's an API
> >>>btrfs inspect-internal min-dev-size /sysroot/
> >>But this API is available only in btrfs-progs >= 4.2.
> >>Before this, there's no reliable way to get minimum size (I could
> >>parse "btrfs filesystem show", but it is veeery inaccurate).
> >>
> >>Can we require btrfs-progs v4.2? Or how should I work-around this issue?
> >Well it's a new API, so we can just tell people they need new
> >btrfs-progs if they want to use the new API.
> >
> >It would be a problem if we were changing an old API, but that's not
> >the case here.
> >
> >Rich.
> OK. I have another question:
> The call for ext works on mounted and unmounted fs.
>               for ntfs on read-only-mounted and unmounted.
>               for btrfs on mounted (ro and rw).
>               for xfs on mounted (ro and rw) (xfs does not support
> shrinking, so guestfs_xfs_info).
> Should we require the user to care about fs mount status / do
> mounts/unmounts ourselves (how to choose mountpoint?) / refuse to
> work if fs is not ro-mounted?
> I would vote for 1st option: include mount check into functions and
> politely report incompatible mount status to user.

Ideally the user wouldn't have to care about the filesystem type, so I
think your solution is the best one.

If you don't do an explicit mount check, is the error message clear
enough?  Doing an actual mount check is complicated.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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