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

[Daniel P . Berrangé]

On Mon, May 23, 2022 at 08:02:45PM +0200, Marc-André Lureau wrote:
> Hi
> 
> On Mon, May 23, 2022 at 7:56 PM Daniel P. Berrangé <berrange@redhat.com>
> wrote:
> 
> > 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.
> >
> >
> It's a bit problematic to make qemu-ga standalone, and have a common shared
> subproject/library.
> 
> Maybe introduce a callback for QEMU/QMP "/dev/fdset" handling ? any better
> idea ?

If we want to make qemu-ga standalone, then IMHO we should be
aggressively switching it to use as many GLib APIs as possible,
eliminating its reliance on any of QEMU's home-grown portability
functions. All the 'FILE *' / 'open' scenarios could be replaced
with GIO's GFile/GInputStream/GOutputStream for example.

With regards,
Daniel
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