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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Feb 27, 2019 at 03:25:22AM -0700, Jan Beulich wrote:
> >>> On 27.02.19 at 00:03, <julien.grall@xxxxxxx> 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.
> 
> We don't need the behavior for internal producers, so I think the change
> touches way too much code. I think all you need to do is make the
> hypercall handler sense null characters, and perhaps simply invoke lower
> level handlers multiple times. Or replace them by something else (e.g. a
> blank).

I don't think replacing NULs with blank is the right thing to do. It's
not only about how human perceives the output, but also about scripting.

Wei.

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