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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'.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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