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Re: [libvirt] [PATCHv4 1/2] virsh: add new --details option to pool-list



On Thu, Jul 01, 2010 at 11:50:20AM +0100, Daniel P. Berrange wrote:
> On Thu, Jul 01, 2010 at 11:38:06AM +0100, Richard W.M. Jones wrote:
> > On Tue, Jun 22, 2010 at 12:35:32PM -0600, Eric Blake wrote:
> > > On 06/22/2010 12:24 PM, Hugh O. Brock wrote:
> > > >> Correct, we shouldn't change this behaviour - it'll break apps parsing
> > > >> the output
> > > > 
> > > > FWIW Rich Jones complains that the output as it stands is nigh on
> > > > unparseable anyway. Perhaps we should consider that a bug, and fix
> > > > it...
> > > 
> > > The new --details option is our chance to change output - it outputs
> > > whatever format we want, because it is a new flag; Rich, do you have any
> > > preferences about what it _should_ output?
> > > 
> > > Here's what pool-list --details would currently do, if we applied
> > > Justin's patch as-is (modulo no line wrapping added by my email client):
> > 
> > Sorry, been away for a couple of weeks.
> > 
> > > virsh # pool-list --details --all
> > > Name       State     Autostart  Persistent  Capacity  Allocation  Available
> > > ---------------------------------------------------------------------------
> > > default    running   yes        yes          1.79 TB     1.49 TB  304.77 GB
> > > image_dir  running   yes        yes          1.79 TB     1.49 TB  304.77 GB
> > > tmp        inactive  no         yes                -           -          -
> > 
> > One good thing, and several bad things about that.  The good thing is
> > that empty columns are presented with '-' which means you can use awk
> > and sort -k to parse the output columnwise.
> > 
> > The bad things:
> > 
> > * Space within fields "1.79 TB" (awk / sort -k in fact _won't_ work).
> > 
> > * Numeric fields aren't numbers: You can't sort -n on "1.79 TB", and
> >   you can't read that number into a script and do math on it.  Most
> >   tools have a "-h" or "--human" option in order to generate human-
> >   readable numbers (without spaces), but default to just printing the
> >   raw numbers.
> > 
> > * Unnecessary "-------" line.
> > 
> > * Title line should be optional.  Have a --no-title option or
> >   something like that to suppress it.
> > 
> > * Does virsh still print an unnecessary blank line after the output?
> >   If so, stop doing that.
> 
> All of these bad things are just an artifact of trying to use the same
> output format for humans & machines. To address all those would make
> the result unpleasant for humans. We really do just need to create a
> dedicated format for machines, csv or json, or somethingelse and leave
> the human format alone

Actually I think we *do* need the --details convenience method for
human-readable output, *and* a better machine-parseable format. Justin
is mostly interested in making virsh more usable for people, which I
fully support -- making it easier to script is also a bonus however.

--Hugh
> 
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