[Qemu-devel] Re: [RFC PATCH 07/20] Introduce qemu_put_vector() and qemu_put_vector_prepare() to use put_vector() in QEMUFile.

[Anthony Liguori]

On 04/22/2010 11:02 PM, Yoshiaki Tamura wrote:
> Anthony Liguori wrote:
> > On 04/21/2010 12:57 AM, Yoshiaki Tamura wrote:
> > > For fool proof purpose, qemu_put_vector_parepare should be called
> > > before qemu_put_vector. Then, if qemu_put_* functions except this is
> > > called after qemu_put_vector_prepare, program will abort().
> > >
> > > Signed-off-by: Yoshiaki Tamura<address@hidden>
> >
> > I don't get it. What's this protecting against?
>
> This was introduced to prevent mixing the order of normal write and 
> vector write, and flush QEMUFile buffer before handling vectors.
> While qemu_put_buffer copies data to QEMUFile buffer, 
> qemu_put_vector() will bypass that buffer.
>
> It's just fool proof purpose for what we encountered at beginning, and 
> if the user of qemu_put_vector() is careful enough, we can remove 
> qemu_put_vectore_prepare().  While writing this message, I started to 
> think that just calling qemu_fflush() in qemu_put_vector() would be 
> enough...

I definitely think removing the vector stuff in the first version would 
simplify the process of getting everything merged.  I'd prefer not to 
have two apis so if vector operations were important from a performance 
perspective, I'd want to see everything converted to a vector API.

Regards,

Anthony Liguori