Re: [Qemu-devel] [PATCH RFC] qemu-char: add an "overlay" backend type

[Paolo Bonzini]

On 16/12/2015 18:56, Daniel P. Berrange wrote:
> Introduce a new QEMU chardev backend called "overlay" which
> allows you to splice together a pair of chardev backends into
> one combined backend. The master backend permits full input/output
> but the slave backend is output only.
> 
> The primary use case for this is to allow arbitrary backends to
> have their data logged to a file, eg a 'file' backend would be
> setup as the slave.
> 
>  $ qemu-system-x86_64 \
>      -chardev socket,host=localhost,port=9000,server=on,nowait,id=char0master 
> \
>      -chardev file,path=/some/log/file.log,id=char0slave \
>      -chardev overlay,id=char0,master=char0master,slave=char0slave  \
>      -device isa-serial,chardev=char0 \
>      ...other args...
> ---
> 
> This idea was suggsted in
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2015-12/msg01256.html
> 
> this patch is a very quick proof of concept impl to illustrate the
> idea.

Hmm, I was a fan of the "do it outside QEMU" idea... It would also fix
the issue you have with qemu_chr_fe_write_all...

Paolo