Re: [Qemu-devel] [PATCH RFC] qemu-io: Prefer stderr for error messages

[Richard W.M. Jones]

On Thu, Dec 13, 2018 at 03:22:10PM +0100, Kevin Wolf wrote:
> Am 13.12.2018 um 11:11 hat Daniel P. Berrangé geschrieben:
> > On Wed, Dec 12, 2018 at 04:04:10PM -0600, Eric Blake wrote:
> > > When a qemu-io command fails, it's best if the failure message
> > > goes to stderr rather than stdout.
> > > 
> > > Reported-by: Richard W.M. Jones <address@hidden>
> > > Signed-off-by: Eric Blake <address@hidden>
> > > ---
> > > 
> > > RFC because at least iotest 60 (found by -qcow2 -g quick) breaks due
> > > to reordering of output lines, and I'd rather know if we like this
> > > idea before bothering to revisit all affected iotests (including
> > > discovering if other slower ones have similar problems).
> > 
> > I think the change is correct. Error messages should never go to stdout.
> 
> I'm not sure about this, to be honest. qemu-io is first and foremost an
> interactive program, and spreading output across two streams, one
> buffered and one unbuffered, in an interactive program feels like it has
> to result in surprises.

Just for the record we're using qemu-io extensively for testing
nbdkit, and it's always used non-interactively (ie. ‘qemu-io -c’).
The bug (if it is such) was found because I was using qemu-io to test
for expected errors.

https://github.com/libguestfs/nbdkit/search?q=qemu-io

Rich.

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