|
| From: | Marc-André Lureau |
| Subject: | Re: [PATCH v12 08/19] multi-process: define MPQemuMsg format and transmission functions |
| Date: | Thu, 10 Dec 2020 12:20:06 +0400 |
On Mon, Dec 07, 2020 at 05:18:46PM +0400, Marc-André Lureau wrote:
> Hi
>
> On Wed, Dec 2, 2020 at 12:25 AM Jagannathan Raman <jag.raman@oracle.com>
> wrote:
>
> > From: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> >
> > Defines MPQemuMsg, which is the message that is sent to the remote
> > process. This message is sent over QIOChannel and is used to
> > command the remote process to perform various tasks.
> > Define transmission functions used by proxy and by remote.
> > There are certain restrictions on where its safe to use these
> > functions:
> > - From main loop in co-routine context. Will block the main loop if not
> > in
> > co-routine context;
> > - From vCPU thread with no co-routine context and if the channel is not
> > part
> > of the main loop handling;
> > - From IOThread within co-routine context, outside of co-routine context
> > will
> > block IOThread;
> >
> > Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> > Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> > Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> > ---
> > include/hw/remote/mpqemu-link.h | 60 ++++++++++
> > hw/remote/mpqemu-link.c | 242
> > ++++++++++++++++++++++++++++++++++++++++
> > MAINTAINERS | 2 +
> > hw/remote/meson.build | 1 +
> > 4 files changed, 305 insertions(+)
> > create mode 100644 include/hw/remote/mpqemu-link.h
> > create mode 100644 hw/remote/mpqemu-link.c
> >
> > diff --git a/include/hw/remote/mpqemu-link.h
> > b/include/hw/remote/mpqemu-link.h
> > new file mode 100644
> > index 0000000..2d79ff8
> > --- /dev/null
> > +++ b/include/hw/remote/mpqemu-link.h
> > @@ -0,0 +1,60 @@
> > +/*
> > + * Communication channel between QEMU and remote device process
> > + *
> > + * Copyright © 2018, 2020 Oracle and/or its affiliates.
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or
> > later.
> > + * See the COPYING file in the top-level directory.
> > + *
> > + */
> > +
> > +#ifndef MPQEMU_LINK_H
> > +#define MPQEMU_LINK_H
> > +
> > +#include "qom/object.h"
> > +#include "qemu/thread.h"
> > +#include "io/channel.h"
> > +
> > +#define REMOTE_MAX_FDS 8
> > +
> > +#define MPQEMU_MSG_HDR_SIZE offsetof(MPQemuMsg, data.u64)
> > +
> > +/**
> > + * MPQemuCmd:
> > + *
> > + * MPQemuCmd enum type to specify the command to be executed on the remote
> > + * device.
> > + */
> > +typedef enum {
> > + MPQEMU_CMD_INIT,
> > + MPQEMU_CMD_MAX,
> > +} MPQemuCmd;
> > +
> > +/**
> > + * MPQemuMsg:
> > + * @cmd: The remote command
> > + * @size: Size of the data to be shared
> > + * @data: Structured data
> > + * @fds: File descriptors to be shared with remote device
> > + *
> > + * MPQemuMsg Format of the message sent to the remote device from QEMU.
> > + *
> > + */
> > +typedef struct {
> > + int cmd;
> > + size_t size;
> > +
> > + union {
> > + uint64_t u64;
> > + } data;
> > +
> > + int fds[REMOTE_MAX_FDS];
> > + int num_fds;
> > +} MPQemuMsg;
> > +
> > +void mpqemu_msg_send(MPQemuMsg *msg, QIOChannel *ioc, Error **errp);
> > +void mpqemu_msg_recv(MPQemuMsg *msg, QIOChannel *ioc, Error **errp);
> > +
> > +bool mpqemu_msg_valid(MPQemuMsg *msg);
> > +
> > +#endif
> > diff --git a/hw/remote/mpqemu-link.c b/hw/remote/mpqemu-link.c
> > new file mode 100644
> > index 0000000..e535ed2
> > --- /dev/null
> > +++ b/hw/remote/mpqemu-link.c
> > @@ -0,0 +1,242 @@
> > +/*
> > + * Communication channel between QEMU and remote device process
> > + *
> > + * Copyright © 2018, 2020 Oracle and/or its affiliates.
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or
> > later.
> > + * See the COPYING file in the top-level directory.
> > + *
> > + */
> > +
> > +#include "qemu/osdep.h"
> > +#include "qemu-common.h"
> > +
> > +#include "qemu/module.h"
> > +#include "hw/remote/mpqemu-link.h"
> > +#include "qapi/error.h"
> > +#include "qemu/iov.h"
> > +#include "qemu/error-report.h"
> > +#include "qemu/main-loop.h"
> > +
> > +/*
> > + * Send message over the ioc QIOChannel.
> > + * This function is safe to call from:
> > + * - From main loop in co-routine context. Will block the main loop if
> > not in
> > + * co-routine context;
> > + * - From vCPU thread with no co-routine context and if the channel is
> > not part
> > + * of the main loop handling;
> > + * - From IOThread within co-routine context, outside of co-routine
> > context
> > + * will block IOThread;
> >
>
> Can drop the extra "From" on each line.
>
> + */
> > +void mpqemu_msg_send(MPQemuMsg *msg, QIOChannel *ioc, Error **errp)
> > +{
> > + bool iolock = qemu_mutex_iothread_locked();
> > + bool iothread = qemu_get_current_aio_context() ==
> > qemu_get_aio_context() ?
> > + false : true;
> >
>
> I would introduce a qemu_in_iothread() helper (similar to
> qemu_in_coroutine() etc)
>
> + Error *local_err = NULL;
> > + struct iovec send[2] = {0};
> > + int *fds = NULL;
> > + size_t nfds = 0;
> > +
> > + send[0].iov_base = msg;
> > + send[0].iov_len = MPQEMU_MSG_HDR_SIZE;
> > +
> > + send[1].iov_base = (void *)&msg->data;
> > + send[1].iov_len = msg->size;
> > +
> > + if (msg->num_fds) {
> > + nfds = msg->num_fds;
> > + fds = msg->fds;
> > + }
> > + /*
> > + * Dont use in IOThread out of co-routine context as
> > + * it will block IOThread.
> > + */
> > + if (iothread) {
> > + assert(qemu_in_coroutine());
> > + }
> >
>
> or simply assert(!iothread || qemu_in_coroutine())
>
> + /*
> > + * Skip unlocking/locking iothread when in IOThread running
> > + * in co-routine context. Co-routine context is asserted above
> > + * for IOThread case.
> > + * Also skip this while in a co-routine in the main context.
> > + */
> > + if (iolock && !iothread && !qemu_in_coroutine()) {
> > + qemu_mutex_unlock_iothread();
> > + }
> > +
> > + (void)qio_channel_writev_full_all(ioc, send, G_N_ELEMENTS(send), fds,
> > nfds,
> > + &local_err);
> >
>
> That extra (void) is probably unnecessary.
>
>
> +
> > + if (iolock && !iothread && !qemu_in_coroutine()) {
> > + /* See above comment why skip locking here. */
> > + qemu_mutex_lock_iothread();
> > + }
> > +
> > + if (errp) {
> > + error_propagate(errp, local_err);
> > + } else if (local_err) {
> > + error_report_err(local_err);
> > + }
> >
>
Hi Marc-Andre,
Thank you for reviewing the patches.
> Not sure this behaviour is recommended. Instead, a trace and an ERRP_GUARD
> would be more idiomatic.
Did you mean to suggest using trace_ functions for the general use, not only the
failure path. Just want to make sure I understood correctly.
Should the trace file subdirectory (in this case ./hw/remote/) be included into
trace_events_subdirs of meson.build with the condition that CONFIG_MULTIPROCESS is enabled?
Something like
<snip>
config_devices_mak_file = target + '-config-devices.mak'
devconfig = keyval.load(meson.current_build_dir() / target + '-config-devices.mak')
have_multiprocess = 'CONFIG_MULTIPROCESS' in devconfig
if have_multiproces
...'
</snip>
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