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



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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