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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.

Rich.

-- 
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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