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Re: [Libguestfs] [PATCH 1/2] New API: btrfs_filesystem_show




> -----Original Message-----
> From: Richard W.M. Jones [mailto:rjones redhat com]
> Sent: Friday, March 06, 2015 4:43 PM
> To: Chen, Hanxiao/陈 晗霄
> Cc: libguestfs redhat com
> Subject: Re: [Libguestfs] [PATCH 1/2] New API: btrfs_filesystem_show
> 
> On Fri, Mar 06, 2015 at 07:39:36AM +0000, Chen, Hanxiao wrote:
> >
> >
> > > -----Original Message-----
> > > From: Richard W.M. Jones [mailto:rjones redhat com]
> > > Sent: Thursday, March 05, 2015 8:59 PM
> > > To: Chen, Hanxiao/陈 晗霄
> > > Cc: libguestfs redhat com
> > > Subject: Re: [Libguestfs] [PATCH 1/2] New API: btrfs_filesystem_show
> > >
> > > AFAICT this API doesn't work:
> > >
> > >   $ ./run guestfish -N fs:btrfs btrfs-filesystem-show /dev/sda1
> > >   libguestfs: error: btrfs_filesystem_show: /dev/sda1:
> > >
> >
> > That might be a bug of btrfs-progs. v3.17 works fine.
> > I'll fix it.
> >
> > > When I tried the btrfs-filesystem-show-all API, I see a lot of
> > > structure in the output:
> > >
> > >   $ ./run guestfish -N fs:btrfs btrfs-filesystem-show-all
> > >   Label: none  uuid: f7754d86-baa1-40e7-a563-46976e81d64c
> > >          Total devices 1 FS bytes used 28.00KiB
> > >          devid    1 size 99.88MiB used 12.00MiB path /dev/sda1
> > >
> > >   Btrfs v3.18
> > >
> > > Usually we should try to turn that text into structs, otherwise every
> > > consumer of libguestfs has to write parsing code themselves.
> > >
> > > *However* in this case I'm having a hard time understanding why anyone
> > > would want to use the API.  Most likely if they were debugging a btrfs
> > > problem, they'd be using 'virt-rescue' and would be able to run
> > > arbitrary commands.  Some of the other information, like UUID and
> > > label is available through other APIs (eg. get-uuid).  Other
> > > information like the layout of devices could be modelled with some
> > > very complex structs on the libguestfs side, but does anyone need
> > > this?
> > >
> >
> > btrfs filesystem show could tell user info when they what to use:
> > btrfs filesystem balance
> >
> > What's more,
> > it could tell us if some of the btrfs device is missing:
> > If we had 10 btrfs devices but one of them is missing, we could use
> > btrfs-filesystem-show to find out which one is missing in a convenient way.
> 
> I don't doubt that it's useful, but these kind of user-facing
> debugging operations would probably be done using 'virt-rescue'.
> 

Thanks for the clarification, I see.

Regards, 
- Chen


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