Re: [Xen-devel] [PATCH for-4.12 RFC] xen/console: Handle NUL character in buffer sent via CONSOLEIO_write

[Julien Grall <julien.grall@xxxxxxx>]

Hi Juergen,

On 3/5/19 12:57 PM, Juergen Gross wrote:
> On 27/02/2019 11:45, Julien Grall wrote:
> > (+ Juergen Gross as RM)
> >
> > I forgot to CC Juergen for this.
> >
> > On 2/26/19 11:03 PM, Julien Grall wrote:
> > > After upgrading Debian to Buster, I started noticing console mangling
> > > when using zsh. This is happenning because output sent by zsh to the
> > > console may contain NUL character in the middle of the buffer.
> > >
> > > Linux is sending the buffer as it is to Xen console via CONSOLEIO_write.
> > > However, the implementation in Xen considers NUL character is used to
> > > terminate the buffer and therefore will ignore anything after it.
> > >
> > > The actual documentation of CONSOLEIO_write is pretty limited. From the
> > > declaration, the hypercall takes a buffer and size. So this could lead
> > > to think the NUL character is allowed in the middle of the buffer.
> > >
> > > This patch updates the console API to pass the size along the buffer
> > > down so we can remove the reliance on buffer terminating by a NUL
> > > character.
> > >
> > > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> The risk for a regression is too high this late in the 4.12 release
> process IMO.
This code path is fairly well tested (console are used pretty much all 
the times). So a regression would be quickly noticed.
This patch has the advantage to allow upgrade to a newer Debian without 
loosing part of your prompt on zsh. I am not sure whether the problem is 
the same with other Distros.
> My plan is to have only one further RC before branching off 4.12,
> so please let us shift this patch to 4.13.
I understand. It is possible to workaround the problem at least with 
zsh. So a release note in Xen (and maybe Debian) should do the job.
Cheers,

--
Julien Grall

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