Re: [PATCH v4 10/11] 9p: darwin: meson: Allow VirtFS on Darwin

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Montag, 7. Februar 2022 15:39:30 CET Greg Kurz wrote:
> On Mon, 07 Feb 2022 15:15:46 +0100
> 
> Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:
> > On Montag, 7. Februar 2022 02:05:32 CET Will Cohen wrote:
> > > On Sun, Feb 6, 2022 at 4:22 PM Philippe Mathieu-Daudé <f4bug@amsat.org>
> > > 
> > > wrote:
> > > > On 6/2/22 21:07, Will Cohen wrote:
> > > > > From: Keno Fischer <keno@juliacomputing.com>
> > > > > 
> > > > > Signed-off-by: Keno Fischer <keno@juliacomputing.com>
> > > > > [Michael Roitzsch: - Rebase for NixOS]
> > > > > Signed-off-by: Michael Roitzsch <reactorcontrol@icloud.com>
> > > > > [Will Cohen: - Rebase to master]
> > > > > Signed-off-by: Will Cohen <wwcohen@gmail.com>
> > > > > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > > > > [Will Cohen: - Add check for pthread_fchdir_np to virtfs]
> > > > > Signed-off-by: Will Cohen <wwcohen@gmail.com>
> > > > > ---
> > > > > 
> > > > >   fsdev/meson.build |  1 +
> > > > >   meson.build       | 14 ++++++++++----
> > > > >   2 files changed, 11 insertions(+), 4 deletions(-)
> > > > > 
> > > > > -have_virtfs_proxy_helper = have_virtfs and have_tools
> > > > > +have_virtfs_proxy_helper = targetos == 'linux' and have_virtfs and
> > > > 
> > > > have_tools
> > > > 
> > > > Why do you restrict the proxy-helper to Linux?
> > > 
> > > Only because porting the proxy-helper to macOS is outside the scope of
> > > this
> > > particular patch. While some initial concepts around it have been
> > > considered by some of the contributors to this patch, those
> > > implementations
> > > weren't tested enough and the security implications weren't considered
> > > in
> > > full. We assume that this could be an additional implementation later
> > > on,
> > > if the functionality is considered important down the road.
> > 
> > In general that's fine with me. I would have probably made that
> > "targetos != 'darwin'" instead of "targetos == 'linux'", but I leave that
> > up to you.
> > 
> > On the long term we will probably deprecate the 9p 'proxy' fs driver
> > anyway. While it had some good ideas, being realistic though: nobody has
> > worked on the 9p proxy driver/backend for many years and it is not in
> > good shape.
> It definitely isn't indeed. Also it is super slow by design
> since the round trip of a 9p request involves QEMU on both entry
> and exit:
> 
>    [guest] --> [QEMU]--> [virtfs-proxy-helper]-->[QEMU]-->[guest]
> 
> A more modern and efficient approach would be to have a vhost-user-9p
> implementation : requests would be directly handled by the external
> process, without QEMU hops. But this a fair amount of work.

That's already a bit offtopic, but how would you imagine that to work? You 
mean a system dependent solution that e.g. plugs in into KVM or something?

> > I can imagine that due to the ground being laid by these series, that we
> > will also open 9p for BSD, but that should be done a bit later and hence
> > does not belong into these series.
> > 
> > But once again: it would not have hurt to make your intentions clear
> > either in the commit log or by in-source comment. :)
> > 
> > Best regards,
> > Christian Schoenebeck