Libguestfs - Oct 2015 - Re: [PATCHv4 0/2] Introduce vfs_minimum_size API to get minimum filesystem size.

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.

-- 
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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.

-- 
Your sincerely,
Maxim Perevedentsev

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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