Re: [PATCH v3 05/15] osdep: export qemu_open_cloexec()

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, May 23, 2022 at 07:30:42PM +0200, Marc-André Lureau wrote:
> Hi
> 
> On Mon, May 23, 2022 at 2:43 PM Daniel P. Berrangé <berrange@redhat.com>
> wrote:
> 
> > On Fri, May 13, 2022 at 08:08:11PM +0200, marcandre.lureau@redhat.com
> > wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Used in the next patch, to simplify qga code.
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >  include/qemu/osdep.h |  1 +
> > >  util/osdep.c         | 10 ++++++++--
> > >  2 files changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > > index 67cc465416..64f51cfb7a 100644
> > > --- a/include/qemu/osdep.h
> > > +++ b/include/qemu/osdep.h
> > > @@ -489,6 +489,7 @@ void sigaction_invoke(struct sigaction *action,
> > >   */
> > >  int qemu_open_old(const char *name, int flags, ...);
> > >  int qemu_open(const char *name, int flags, Error **errp);
> > > +int qemu_open_cloexec(const char *name, int flags, mode_t mode, Error
> > **errp);
> >
> > I don't think we should be exporting this - it is just a variant of the
> > 'qemu_open_old' method that we wanted callers to stop using in favour
> > of explicitly deciding between 'qemu_open' and 'qemu_create'.
> >
> 
> 
> qemu_open() has "/dev/fdset" handling, which qemu-ga and other tools don't
> need.

Right, but exporting this as 'qemu_open_cloexec' is going to mislead
people into thinking it is a better version of 'qemu_open'. This will
cause us to loose support for /dev/fdset in places where we actually
need it.

It is pretty harmless to have /dev/fdset there, even if the tool does
not need it - that's been the case with many QEMU tools for many years.
If we think it is actually a real problem though, we should just have
a way to toggle it on/off from the existing APIs.

eg put  'bool allow_fdset = true"   in softmmu/vl.c, and
'bool allow_fdset = false' in stubs/open.c, and then make
qemu_open_internal conditionalize itself on this global 
variable, so only the system emulators get fdset support
activated.

With regards,
Daniel
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