[Xen-devel] [PATCH 2/3] libxl_qmp: Command migrate.

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This command works in two steps. First, a fd is sent to QEMU through the QMP
socket. And then, the second command "migrate" use the fd previously sent to
ask QEMU to save its states.

This come with an alternative qmp_send function that can send a fd.

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/libxl/libxl_internal.h |    2 +
 tools/libxl/libxl_qmp.c      |  109 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 111 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 84da6b1..e4afd2b 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -528,6 +528,8 @@ _hidden int libxl__qmp_query_serial(libxl__qmp_handler 
*qmp);
 _hidden int libxl__qmp_pci_add(libxl__gc *gc, int d, libxl_device_pci *pcidev);
 _hidden int libxl__qmp_pci_del(libxl__gc *gc, int domid,
                                libxl_device_pci *pcidev);
+/* Save current QEMU state into fd. */
+_hidden int libxl__qmp_migrate(libxl__gc *gc, int domid, int fd);
 /* close and free the QMP handler */
 _hidden void libxl__qmp_close(libxl__qmp_handler *qmp);
 /* remove the socket file, if the file has already been removed,
diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
index 99ab4fa..891ca9e 100644
--- a/tools/libxl/libxl_qmp.c
+++ b/tools/libxl/libxl_qmp.c
@@ -532,6 +532,52 @@ out:
     return rc;
 }
 
+static int qmp_send_fd(libxl__gc *gc, libxl__qmp_handler *qmp,
+                       libxl_key_value_list *args,
+                       qmp_callback_t callback, void *opaque,
+                       qmp_request_context *context,
+                       int fd)
+{
+    struct msghdr msg = { 0 };
+    struct cmsghdr *cmsg;
+    char control[CMSG_SPACE(sizeof (fd))];
+    struct iovec iov;
+    char *buf = NULL;
+
+    buf = qmp_send_prepare(gc, qmp, "getfd", args, callback, opaque, context);
+
+    /* Response data */
+    iov.iov_base = buf;
+    iov.iov_len  = strlen(buf);
+
+    /* compose the message */
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+    msg.msg_control = control;
+    msg.msg_controllen = sizeof (control);
+
+    /* attach open fd */
+    cmsg = CMSG_FIRSTHDR(&msg);
+    cmsg->cmsg_level = SOL_SOCKET;
+    cmsg->cmsg_type = SCM_RIGHTS;
+    cmsg->cmsg_len = CMSG_LEN(sizeof (fd));
+    *(int *)CMSG_DATA(cmsg) = fd;
+
+    msg.msg_controllen = cmsg->cmsg_len;
+
+    if (sendmsg(qmp->qmp_fd, &msg, 0) < 0) {
+        LIBXL__LOG_ERRNO(qmp->ctx, LIBXL__LOG_ERROR,
+                         "Failed to send a QMP message to QEMU.");
+        return ERROR_FAIL;
+    }
+    if (libxl_write_exactly(qmp->ctx, qmp->qmp_fd, "\r\n", 2,
+                            "CRLF", "QMP socket")) {
+        return ERROR_FAIL;
+    }
+
+    return qmp->last_id_used;
+}
+
 static int qmp_synchronous_send(libxl__qmp_handler *qmp, const char *cmd,
                                 libxl_key_value_list *args,
                                 qmp_callback_t callback, void *opaque,
@@ -768,6 +814,69 @@ int libxl__qmp_pci_del(libxl__gc *gc, int domid, 
libxl_device_pci *pcidev)
     return qmp_device_del(gc, domid, id);
 }
 
+static int qmp_getfd(libxl__gc *gc, libxl__qmp_handler *qmp,
+                     int fd, const char *name)
+{
+    flexarray_t *parameters = NULL;
+    libxl_key_value_list args = NULL;
+    int rc = 0;
+
+    parameters = flexarray_make(2, 1);
+    if (!parameters)
+        return ERROR_NOMEM;
+    flexarray_append_pair(parameters, "fdname", (char*)name);
+    args = libxl__xs_kvs_of_flexarray(gc, parameters, parameters->count);
+    if (!args) {
+        rc = ERROR_NOMEM;
+        goto out;
+    }
+
+    if (qmp_send_fd(gc, qmp, &args, NULL, NULL, NULL, fd) < 0) {
+        rc = ERROR_FAIL;
+    }
+out:
+    flexarray_free(parameters);
+    return rc;
+}
+
+int libxl__qmp_migrate(libxl__gc *gc, int domid, int fd)
+{
+#define MIGRATE_FD_NAME "dm-migrate"
+    libxl__qmp_handler *qmp = NULL;
+    flexarray_t *parameters = NULL;
+    libxl_key_value_list args = NULL;
+    int rc = 0;
+
+    qmp = libxl__qmp_initialize(libxl__gc_owner(gc), domid);
+    if (!qmp)
+        return ERROR_FAIL;
+
+    rc = qmp_getfd(gc, qmp, fd, MIGRATE_FD_NAME);
+    if (rc)
+        goto out;
+
+    parameters = flexarray_make(2, 1);
+    if (!parameters) {
+        rc = ERROR_NOMEM;
+        goto out;
+    }
+    flexarray_append_pair(parameters, "uri", "fd:" MIGRATE_FD_NAME);
+    args = libxl__xs_kvs_of_flexarray(gc, parameters, parameters->count);
+    if (!args) {
+        rc = ERROR_NOMEM;
+        goto out2;
+    }
+
+    rc = qmp_synchronous_send(qmp, "migrate", &args,
+                              NULL, NULL, qmp->timeout);
+
+out2:
+    flexarray_free(parameters);
+out:
+    libxl__qmp_close(qmp);
+    return rc;
+}
+
 int libxl__qmp_initializations(libxl_ctx *ctx, uint32_t domid)
 {
     libxl__qmp_handler *qmp = NULL;
-- 
Anthony PERARD


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