[PATCH v10 06/19] multi-process: define MPQemuMsg format and transmission functions

[elena.ufimtseva@oracle.com]

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>
---
 MAINTAINERS              |   2 +
 include/io/mpqemu-link.h |  60 ++++++++++
 io/meson.build           |   2 +
 io/mpqemu-link.c         | 230 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 294 insertions(+)
 create mode 100644 include/io/mpqemu-link.h
 create mode 100644 io/mpqemu-link.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 38d19c83cd..1ca1f8ccff 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3045,6 +3045,8 @@ F: hw/pci-host/remote.c
 F: include/hw/pci-host/remote.h
 F: hw/i386/remote.c
 F: include/hw/i386/remote.h
+F: io/mpqemu-link.c
+F: include/io/mpqemu-link.h
 
 Build and test automation
 -------------------------
diff --git a/include/io/mpqemu-link.h b/include/io/mpqemu-link.h
new file mode 100644
index 0000000000..3505e062dd
--- /dev/null
+++ b/include/io/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;
+} QEMU_PACKED 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/io/meson.build b/io/meson.build
index 768c1b5ec3..3d40cd8867 100644
--- a/io/meson.build
+++ b/io/meson.build
@@ -15,6 +15,8 @@ io_ss.add(files(
   'task.c',
 ))
 
+io_ss.add(when: 'CONFIG_MPQEMU', if_true: files('mpqemu-link.c'))
+
 io_ss = io_ss.apply(config_host, strict: false)
 libio = static_library('io', io_ss.sources() + genh,
                        dependencies: [io_ss.dependencies()],
diff --git a/io/mpqemu-link.c b/io/mpqemu-link.c
new file mode 100644
index 0000000000..42df2af229
--- /dev/null
+++ b/io/mpqemu-link.c
@@ -0,0 +1,230 @@
+/*
+ * 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 "io/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;
+ */
+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;
+    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());
+    }
+    /*
+     * 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);
+
+    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);
+    }
+
+    return;
+}
+
+/*
+ * Read message from 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;
+ */
+static ssize_t mpqemu_read(QIOChannel *ioc, void *buf, size_t len, int **fds,
+                           size_t *nfds, Error **errp)
+{
+    struct iovec iov = { .iov_base = buf, .iov_len = len };
+    bool iolock = qemu_mutex_iothread_locked();
+    bool iothread = qemu_get_current_aio_context() == qemu_get_aio_context()
+                        ? false : true;
+    struct iovec *iovp = &iov;
+    Error *local_err = NULL;
+    unsigned int niov = 1;
+    size_t *l_nfds = nfds;
+    int **l_fds = fds;
+    ssize_t bytes = 0;
+    size_t size;
+
+    size = iov.iov_len;
+
+    /*
+     * Dont use in IOThread out of co-routine context as
+     * it will block IOThread.
+     */
+    if (iothread) {
+        assert(qemu_in_coroutine());
+    }
+
+    while (size > 0) {
+        bytes = qio_channel_readv_full(ioc, iovp, niov, l_fds, l_nfds,
+                                       &local_err);
+        if (bytes == QIO_CHANNEL_ERR_BLOCK) {
+            /*
+             * 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();
+            }
+            if (qemu_in_coroutine()) {
+                qio_channel_yield(ioc, G_IO_IN);
+            } else {
+                qio_channel_wait(ioc, G_IO_IN);
+            }
+            /* See above comment why skip locking here. */
+            if (iolock && !iothread && !qemu_in_coroutine()) {
+                qemu_mutex_lock_iothread();
+            }
+            continue;
+        }
+
+        if (bytes <= 0) {
+            error_propagate(errp, local_err);
+            return -EIO;
+        }
+
+        l_fds = NULL;
+        l_nfds = NULL;
+
+        size -= bytes;
+
+        (void)iov_discard_front(&iovp, &niov, bytes);
+    }
+
+    return len - size;
+}
+
+void mpqemu_msg_recv(MPQemuMsg *msg, QIOChannel *ioc, Error **errp)
+{
+    Error *local_err = NULL;
+    int *fds = NULL;
+    size_t nfds = 0;
+    ssize_t len;
+
+    len = mpqemu_read(ioc, (void *)msg, MPQEMU_MSG_HDR_SIZE, &fds, &nfds,
+                      &local_err);
+    if (!local_err) {
+        if (len == -EIO) {
+            error_setg(&local_err, "Connection closed.");
+            goto fail;
+        }
+        if (len < 0) {
+            error_setg(&local_err, "Message length is less than 0");
+            goto fail;
+        }
+        if (len != MPQEMU_MSG_HDR_SIZE) {
+            error_setg(&local_err, "Message header corrupted");
+            goto fail;
+        }
+    } else {
+        goto fail;
+    }
+
+    if (msg->size > sizeof(msg->data)) {
+        error_setg(&local_err, "Invalid size for message");
+        goto fail;
+    }
+
+    if (mpqemu_read(ioc, (void *)&msg->data, msg->size, NULL, NULL,
+                    &local_err) < 0) {
+        goto fail;
+    }
+
+    msg->num_fds = nfds;
+    if (nfds) {
+        memcpy(msg->fds, fds, nfds * sizeof(int));
+    }
+
+fail:
+    if (errp) {
+        error_propagate(errp, local_err);
+    } else if (local_err) {
+        error_report_err(local_err);
+    }
+}
+
+bool mpqemu_msg_valid(MPQemuMsg *msg)
+{
+    if (msg->cmd >= MPQEMU_CMD_MAX && msg->cmd < 0) {
+        return false;
+    }
+
+    /* Verify FDs. */
+    if (msg->num_fds >= REMOTE_MAX_FDS) {
+        return false;
+    }
+
+    if (msg->num_fds > 0) {
+        for (int i = 0; i < msg->num_fds; i++) {
+            if (fcntl(msg->fds[i], F_GETFL) == -1) {
+                return false;
+            }
+        }
+    }
+
+    return true;
+}
-- 
2.25.GIT