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Re: [Qemu-devel] [RFC v2 11/32] vhub: Open userfaultfd
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC v2 11/32] vhub: Open userfaultfd |
Date: |
Fri, 15 Sep 2017 18:33:42 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
* Peter Xu (address@hidden) wrote:
> On Thu, Aug 24, 2017 at 08:27:09PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > Open a userfaultfd (on a postcopy_advise) and send it back in
> > the reply to the qemu for it to monitor.
> >
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> > contrib/libvhost-user/libvhost-user.c | 26 +++++++++++++++++++++++---
> > contrib/libvhost-user/libvhost-user.h | 3 +++
> > 2 files changed, 26 insertions(+), 3 deletions(-)
> >
> > diff --git a/contrib/libvhost-user/libvhost-user.c
> > b/contrib/libvhost-user/libvhost-user.c
> > index 47884c0a15..f9b5b12b28 100644
> > --- a/contrib/libvhost-user/libvhost-user.c
> > +++ b/contrib/libvhost-user/libvhost-user.c
> > @@ -15,6 +15,7 @@
> >
> > #include <qemu/osdep.h>
> > #include <sys/eventfd.h>
> > +#include <sys/syscall.h>
> > #include <linux/vhost.h>
> >
> > #include "qemu/atomic.h"
> > @@ -773,11 +774,30 @@ vu_set_vring_enable_exec(VuDev *dev, VhostUserMsg
> > *vmsg)
> > static bool
> > vu_set_postcopy_advise(VuDev *dev, VhostUserMsg *vmsg)
> > {
> > - /* TODO: Open ufd, pass it back in the request
> > - * TODO: Add addresses
> > - */
> > + struct uffdio_api api_struct;
> > +
> > + dev->postcopy_ufd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
> > + /* TODO: Add addresses */
> > vmsg->payload.u64 = 0xcafe;
> > vmsg->size = sizeof(vmsg->payload.u64);
> > +
> > + if (dev->postcopy_ufd == -1) {
> > + vu_panic(dev, "Userfaultfd not available: %s", strerror(errno));
> > + goto out;
>
> We got error but still goto out? I feel like we should reply with
> some kind of error code when any error happens.
See that the out: code returns the dev->postcopy_ufd to qemu
and in this case it's -1 so it is already flagged as an error.
> > + }
> > + api_struct.api = UFFD_API;
> > + api_struct.features = 0;
> > + if (ioctl(dev->postcopy_ufd, UFFDIO_API, &api_struct)) {
> > + vu_panic(dev, "Failed UFFDIO_API: %s", strerror(errno));
> > + close(dev->postcopy_ufd);
> > + dev->postcopy_ufd = -1;
> > + goto out;
>
> Same here.
And there we explicitly set dev->postcopy_ufd = -1 before going to out
so it's sent as the error value.
> > + }
> > + /* TODO: Stash feature flags somewhere */
> > +out:
> > + /* Return a ufd to the QEMU */
> > + vmsg->fd_num = 1;
> > + vmsg->fds[0] = dev->postcopy_ufd;
^^^ see that's where the -1's end up.
> > return true; /* = send a reply */
> > }
Dave
> >
> > diff --git a/contrib/libvhost-user/libvhost-user.h
> > b/contrib/libvhost-user/libvhost-user.h
> > index 3987ce643d..3e8efdd919 100644
> > --- a/contrib/libvhost-user/libvhost-user.h
> > +++ b/contrib/libvhost-user/libvhost-user.h
> > @@ -234,6 +234,9 @@ struct VuDev {
> > * re-initialize */
> > vu_panic_cb panic;
> > const VuDevIface *iface;
> > +
> > + /* Postcopy data */
> > + int postcopy_ufd;
> > };
> >
> > typedef struct VuVirtqElement {
> > --
> > 2.13.5
> >
>
> --
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK