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Tue, 3 Mar 2020 19:56:43 +0000 (UTC) Received: from work-vm (ovpn-117-2.ams2.redhat.com [10.36.117.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6586690782; Tue, 3 Mar 2020 19:56:30 +0000 (UTC) Date: Tue, 3 Mar 2020 19:56:27 +0000 From: "Dr. David Alan Gilbert" To: Jagannathan Raman Subject: Re: [PATCH v5 08/50] multi-process: add functions to synchronize proxy and remote endpoints Message-ID: <20200303195627.GW3170@work-vm> References: <3d013f0091ac6babb55f30cadf6ed806c322b7ce.1582576372.git.jag.raman@oracle.com> MIME-Version: 1.0 In-Reply-To: <3d013f0091ac6babb55f30cadf6ed806c322b7ce.1582576372.git.jag.raman@oracle.com> User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: elena.ufimtseva@oracle.com, fam@euphon.net, swapnil.ingle@nutanix.com, john.g.johnson@oracle.com, qemu-devel@nongnu.org, kraxel@redhat.com, quintela@redhat.com, mst@redhat.com, armbru@redhat.com, kanth.ghatraju@oracle.com, felipe@nutanix.com, thuth@redhat.com, ehabkost@redhat.com, konrad.wilk@oracle.com, liran.alon@oracle.com, stefanha@redhat.com, thanos.makatos@nutanix.com, rth@twiddle.net, kwolf@redhat.com, berrange@redhat.com, mreitz@redhat.com, ross.lagerwall@citrix.com, marcandre.lureau@gmail.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Jagannathan Raman (jag.raman@oracle.com) wrote: > In some cases, for example MMIO read, QEMU has to wait for the remote to > complete a command before proceeding. An eventfd based mechanism is > added to synchronize QEMU & remote process. >=20 > Signed-off-by: John G Johnson > Signed-off-by: Jagannathan Raman > Signed-off-by: Elena Ufimtseva > --- > include/io/mpqemu-link.h | 7 +++++++ > io/mpqemu-link.c | 41 +++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 48 insertions(+) >=20 > diff --git a/include/io/mpqemu-link.h b/include/io/mpqemu-link.h > index 2f2dd83..ae04fca 100644 > --- a/include/io/mpqemu-link.h > +++ b/include/io/mpqemu-link.h > @@ -135,4 +135,11 @@ void mpqemu_link_set_callback(MPQemuLinkState *s, > mpqemu_link_callback callback); > void mpqemu_start_coms(MPQemuLinkState *s); > =20 > +#define GET_REMOTE_WAIT eventfd(0, EFD_CLOEXEC) > +#define PUT_REMOTE_WAIT(wait) close(wait) > +#define PROXY_LINK_WAIT_DONE 1 > + > +uint64_t wait_for_remote(int efd); > +void notify_proxy(int fd, uint64_t val); > + > #endif > diff --git a/io/mpqemu-link.c b/io/mpqemu-link.c > index bac120b..73b7032 100644 > --- a/io/mpqemu-link.c > +++ b/io/mpqemu-link.c > @@ -10,6 +10,7 @@ > =20 > #include "qemu/osdep.h" > #include "qemu-common.h" > +#include > =20 > #include "qemu/module.h" > #include "io/mpqemu-link.h" > @@ -216,6 +217,46 @@ int mpqemu_msg_recv(MPQemuMsg *msg, MPQemuChannel *c= han) > return rc; > } > =20 > +uint64_t wait_for_remote(int efd) > +{ > + struct pollfd pfd =3D { .fd =3D efd, .events =3D POLLIN }; > + uint64_t val; > + int ret; > + > + ret =3D poll(&pfd, 1, 1000); > + > + switch (ret) { > + case 0: > + qemu_log_mask(LOG_REMOTE_DEBUG, "Error wait_for_remote: Timed ou= t\n"); > + /* TODO: Kick-off error recovery */ > + return ULLONG_MAX; Shouldn't these be UINT64_MAX? > + case -1: > + qemu_log_mask(LOG_REMOTE_DEBUG, "Poll error wait_for_remote: %s\= n", > + strerror(errno)); > + return ULLONG_MAX; > + default: > + if (read(efd, &val, sizeof(val)) =3D=3D -1) { > + qemu_log_mask(LOG_REMOTE_DEBUG, "Error wait_for_remote: %s\n= ", > + strerror(errno)); > + return ULLONG_MAX; > + } > + } > + > + val =3D (val =3D=3D ULLONG_MAX) ? val : (val - 1); Can you explain what's going on there?? > + return val; > +} > + > +void notify_proxy(int efd, uint64_t val) > +{ > + val =3D (val =3D=3D ULLONG_MAX) ? val : (val + 1); > + > + if (write(efd, &val, sizeof(val)) =3D=3D -1) { I'd actually check the write/read's are returning sizeof(val) - they can on a bad day return 0 or send only a few bytes; in theory? Dave > + qemu_log_mask(LOG_REMOTE_DEBUG, "Error notify_proxy: %s\n", > + strerror(errno)); > + } > +} > + > static gboolean mpqemu_link_handler_prepare(GSource *gsrc, gint *timeout= ) > { > g_assert(timeout); > --=20 > 1.8.3.1 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK