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[Xen-devel] [PATCH v2 20/20] xen/tools: VM forking toolstack side



Add necessary bits to implement "xl fork-vm", "xl fork-launch-dm" and
"xl fork-reset" commands. The process is split in two to allow tools needing
access to the new VM as fast as possible after it was forked. It is expected
that under certain use-cases the second command that launches QEMU will be
skipped entirely.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
---
 tools/libxc/include/xenctrl.h |   6 +
 tools/libxc/xc_memshr.c       |  22 ++++
 tools/libxl/libxl.h           |   7 +
 tools/libxl/libxl_create.c    | 237 +++++++++++++++++++++++-----------
 tools/libxl/libxl_dm.c        |   2 +-
 tools/libxl/libxl_dom.c       |  83 ++++++++----
 tools/libxl/libxl_internal.h  |   1 +
 tools/libxl/libxl_types.idl   |   1 +
 tools/xl/xl.h                 |   5 +
 tools/xl/xl_cmdtable.c        |  22 ++++
 tools/xl/xl_saverestore.c     |  96 ++++++++++++++
 tools/xl/xl_vmcontrol.c       |   8 ++
 12 files changed, 386 insertions(+), 104 deletions(-)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index b5ffa53d55..39afdb9b33 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -2221,6 +2221,12 @@ int xc_memshr_range_share(xc_interface *xch,
                           uint64_t first_gfn,
                           uint64_t last_gfn);
 
+int xc_memshr_fork(xc_interface *xch,
+                   uint32_t source_domain,
+                   uint32_t client_domain);
+
+int xc_memshr_fork_reset(xc_interface *xch, uint32_t forked_domain);
+
 /* Debug calls: return the number of pages referencing the shared frame backing
  * the input argument. Should be one or greater.
  *
diff --git a/tools/libxc/xc_memshr.c b/tools/libxc/xc_memshr.c
index 5ef56a6933..ef5a5ee6a4 100644
--- a/tools/libxc/xc_memshr.c
+++ b/tools/libxc/xc_memshr.c
@@ -237,6 +237,28 @@ int xc_memshr_debug_gref(xc_interface *xch,
     return xc_memshr_memop(xch, domid, &mso);
 }
 
+int xc_memshr_fork(xc_interface *xch, uint32_t pdomid, uint32_t domid)
+{
+    xen_mem_sharing_op_t mso;
+
+    memset(&mso, 0, sizeof(mso));
+
+    mso.op = XENMEM_sharing_op_fork;
+    mso.u.fork.parent_domain = pdomid;
+
+    return xc_memshr_memop(xch, domid, &mso);
+}
+
+int xc_memshr_fork_reset(xc_interface *xch, uint32_t domid)
+{
+    xen_mem_sharing_op_t mso;
+
+    memset(&mso, 0, sizeof(mso));
+    mso.op = XENMEM_sharing_op_fork_reset;
+
+    return xc_memshr_memop(xch, domid, &mso);
+}
+
 int xc_memshr_audit(xc_interface *xch)
 {
     xen_mem_sharing_op_t mso;
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 54abb9db1f..75cb070587 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -1536,6 +1536,13 @@ int libxl_domain_create_new(libxl_ctx *ctx, 
libxl_domain_config *d_config,
                             const libxl_asyncop_how *ao_how,
                             const libxl_asyncprogress_how *aop_console_how)
                             LIBXL_EXTERNAL_CALLERS_ONLY;
+int libxl_domain_fork_vm(libxl_ctx *ctx, uint32_t pdomid, uint32_t *domid)
+                             LIBXL_EXTERNAL_CALLERS_ONLY;
+int libxl_domain_fork_launch_dm(libxl_ctx *ctx, libxl_domain_config *d_config,
+                                uint32_t domid,
+                                const libxl_asyncprogress_how *aop_console_how)
+                                LIBXL_EXTERNAL_CALLERS_ONLY;
+int libxl_domain_fork_reset(libxl_ctx *ctx, uint32_t domid);
 int libxl_domain_create_restore(libxl_ctx *ctx, libxl_domain_config *d_config,
                                 uint32_t *domid, int restore_fd,
                                 int send_back_fd,
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 32d45dcef0..e0d219596c 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -536,12 +536,12 @@ out:
     return ret;
 }
 
-int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
-                       libxl__domain_build_state *state,
-                       uint32_t *domid)
+static int libxl__domain_make_xs_entries(libxl__gc *gc, libxl_domain_config 
*d_config,
+                                         libxl__domain_build_state *state,
+                                         uint32_t domid)
 {
     libxl_ctx *ctx = libxl__gc_owner(gc);
-    int ret, rc, nb_vm;
+    int rc, nb_vm;
     const char *dom_type;
     char *uuid_string;
     char *dom_path, *vm_path, *libxl_path;
@@ -553,7 +553,6 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
 
     /* convenience aliases */
     libxl_domain_create_info *info = &d_config->c_info;
-    libxl_domain_build_info *b_info = &d_config->b_info;
 
     uuid_string = libxl__uuid2string(gc, info->uuid);
     if (!uuid_string) {
@@ -561,64 +560,7 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
         goto out;
     }
 
-    /* Valid domid here means we're soft resetting. */
-    if (!libxl_domid_valid_guest(*domid)) {
-        struct xen_domctl_createdomain create = {
-            .ssidref = info->ssidref,
-            .max_vcpus = b_info->max_vcpus,
-            .max_evtchn_port = b_info->event_channels,
-            .max_grant_frames = b_info->max_grant_frames,
-            .max_maptrack_frames = b_info->max_maptrack_frames,
-        };
-
-        if (info->type != LIBXL_DOMAIN_TYPE_PV) {
-            create.flags |= XEN_DOMCTL_CDF_hvm;
-            create.flags |=
-                libxl_defbool_val(info->hap) ? XEN_DOMCTL_CDF_hap : 0;
-            create.flags |=
-                libxl_defbool_val(info->oos) ? 0 : XEN_DOMCTL_CDF_oos_off;
-        }
-
-        assert(info->passthrough != LIBXL_PASSTHROUGH_DEFAULT);
-        LOG(DETAIL, "passthrough: %s",
-            libxl_passthrough_to_string(info->passthrough));
-
-        if (info->passthrough != LIBXL_PASSTHROUGH_DISABLED)
-            create.flags |= XEN_DOMCTL_CDF_iommu;
-
-        if (info->passthrough == LIBXL_PASSTHROUGH_SYNC_PT)
-            create.iommu_opts |= XEN_DOMCTL_IOMMU_no_sharept;
-
-        /* Ultimately, handle is an array of 16 uint8_t, same as uuid */
-        libxl_uuid_copy(ctx, (libxl_uuid *)&create.handle, &info->uuid);
-
-        ret = libxl__arch_domain_prepare_config(gc, d_config, &create);
-        if (ret < 0) {
-            LOGED(ERROR, *domid, "fail to get domain config");
-            rc = ERROR_FAIL;
-            goto out;
-        }
-
-        ret = xc_domain_create(ctx->xch, domid, &create);
-        if (ret < 0) {
-            LOGED(ERROR, *domid, "domain creation fail");
-            rc = ERROR_FAIL;
-            goto out;
-        }
-
-        rc = libxl__arch_domain_save_config(gc, d_config, state, &create);
-        if (rc < 0)
-            goto out;
-    }
-
-    ret = xc_cpupool_movedomain(ctx->xch, info->poolid, *domid);
-    if (ret < 0) {
-        LOGED(ERROR, *domid, "domain move fail");
-        rc = ERROR_FAIL;
-        goto out;
-    }
-
-    dom_path = libxl__xs_get_dompath(gc, *domid);
+    dom_path = libxl__xs_get_dompath(gc, domid);
     if (!dom_path) {
         rc = ERROR_FAIL;
         goto out;
@@ -626,12 +568,12 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
 
     vm_path = GCSPRINTF("/vm/%s", uuid_string);
     if (!vm_path) {
-        LOGD(ERROR, *domid, "cannot allocate create paths");
+        LOGD(ERROR, domid, "cannot allocate create paths");
         rc = ERROR_FAIL;
         goto out;
     }
 
-    libxl_path = libxl__xs_libxl_path(gc, *domid);
+    libxl_path = libxl__xs_libxl_path(gc, domid);
     if (!libxl_path) {
         rc = ERROR_FAIL;
         goto out;
@@ -642,10 +584,10 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
 
     roperm[0].id = 0;
     roperm[0].perms = XS_PERM_NONE;
-    roperm[1].id = *domid;
+    roperm[1].id = domid;
     roperm[1].perms = XS_PERM_READ;
 
-    rwperm[0].id = *domid;
+    rwperm[0].id = domid;
     rwperm[0].perms = XS_PERM_NONE;
 
 retry_transaction:
@@ -663,7 +605,7 @@ retry_transaction:
                     noperm, ARRAY_SIZE(noperm));
 
     xs_write(ctx->xsh, t, GCSPRINTF("%s/vm", dom_path), vm_path, 
strlen(vm_path));
-    rc = libxl__domain_rename(gc, *domid, 0, info->name, t);
+    rc = libxl__domain_rename(gc, domid, 0, info->name, t);
     if (rc)
         goto out;
 
@@ -740,7 +682,7 @@ retry_transaction:
 
     vm_list = libxl_list_vm(ctx, &nb_vm);
     if (!vm_list) {
-        LOGD(ERROR, *domid, "cannot get number of running guests");
+        LOGD(ERROR, domid, "cannot get number of running guests");
         rc = ERROR_FAIL;
         goto out;
     }
@@ -764,7 +706,7 @@ retry_transaction:
             t = 0;
             goto retry_transaction;
         }
-        LOGED(ERROR, *domid, "domain creation ""xenstore transaction commit 
failed");
+        LOGED(ERROR, domid, "domain creation ""xenstore transaction commit 
failed");
         rc = ERROR_FAIL;
         goto out;
     }
@@ -776,6 +718,80 @@ retry_transaction:
     return rc;
 }
 
+int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
+                       libxl__domain_build_state *state,
+                       uint32_t *domid)
+{
+    libxl_ctx *ctx = libxl__gc_owner(gc);
+    int ret, rc;
+
+    /* convenience aliases */
+    libxl_domain_create_info *info = &d_config->c_info;
+    libxl_domain_build_info *b_info = &d_config->b_info;
+
+    /* Valid domid here means we're soft resetting. */
+    if (!libxl_domid_valid_guest(*domid)) {
+        struct xen_domctl_createdomain create = {
+            .ssidref = info->ssidref,
+            .max_vcpus = b_info->max_vcpus,
+            .max_evtchn_port = b_info->event_channels,
+            .max_grant_frames = b_info->max_grant_frames,
+            .max_maptrack_frames = b_info->max_maptrack_frames,
+        };
+
+        if (info->type != LIBXL_DOMAIN_TYPE_PV) {
+            create.flags |= XEN_DOMCTL_CDF_hvm;
+            create.flags |=
+                libxl_defbool_val(info->hap) ? XEN_DOMCTL_CDF_hap : 0;
+            create.flags |=
+                libxl_defbool_val(info->oos) ? 0 : XEN_DOMCTL_CDF_oos_off;
+        }
+
+        assert(info->passthrough != LIBXL_PASSTHROUGH_DEFAULT);
+        LOG(DETAIL, "passthrough: %s",
+            libxl_passthrough_to_string(info->passthrough));
+
+        if (info->passthrough != LIBXL_PASSTHROUGH_DISABLED)
+            create.flags |= XEN_DOMCTL_CDF_iommu;
+
+        if (info->passthrough == LIBXL_PASSTHROUGH_SYNC_PT)
+            create.iommu_opts |= XEN_DOMCTL_IOMMU_no_sharept;
+
+        /* Ultimately, handle is an array of 16 uint8_t, same as uuid */
+        libxl_uuid_copy(ctx, (libxl_uuid *)&create.handle, &info->uuid);
+
+        ret = libxl__arch_domain_prepare_config(gc, d_config, &create);
+        if (ret < 0) {
+            LOGED(ERROR, *domid, "fail to get domain config");
+            rc = ERROR_FAIL;
+            goto out;
+        }
+
+        ret = xc_domain_create(ctx->xch, domid, &create);
+        if (ret < 0) {
+            LOGED(ERROR, *domid, "domain creation fail");
+            rc = ERROR_FAIL;
+            goto out;
+        }
+
+        rc = libxl__arch_domain_save_config(gc, d_config, state, &create);
+        if (rc < 0)
+            goto out;
+    }
+
+    ret = xc_cpupool_movedomain(ctx->xch, info->poolid, *domid);
+    if (ret < 0) {
+        LOGED(ERROR, *domid, "domain move fail");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = libxl__domain_make_xs_entries(gc, d_config, state, *domid);
+
+out:
+    return rc;
+}
+
 static int store_libxl_entry(libxl__gc *gc, uint32_t domid,
                              libxl_domain_build_info *b_info)
 {
@@ -1097,15 +1113,31 @@ static void initiate_domain_create(libxl__egc *egc,
     ret = libxl__domain_config_setdefault(gc,d_config,domid);
     if (ret) goto error_out;
 
-    ret = libxl__domain_make(gc, d_config, &dcs->build_state, &domid);
-    if (ret) {
-        LOGD(ERROR, domid, "cannot make domain: %d", ret);
+    if ( !d_config->dm_restore_file )
+    {
+        ret = libxl__domain_make(gc, d_config, &dcs->build_state, &domid);
         dcs->guest_domid = domid;
+
+        if (ret) {
+            LOGD(ERROR, domid, "cannot make domain: %d", ret);
+            ret = ERROR_FAIL;
+            goto error_out;
+        }
+    } else if ( dcs->guest_domid != INVALID_DOMID ) {
+        domid = dcs->guest_domid;
+
+        ret = libxl__domain_make_xs_entries(gc, d_config, &dcs->build_state, 
domid);
+        if (ret) {
+            LOGD(ERROR, domid, "cannot make domain: %d", ret);
+            ret = ERROR_FAIL;
+            goto error_out;
+        }
+    } else {
+        LOGD(ERROR, domid, "cannot make domain");
         ret = ERROR_FAIL;
         goto error_out;
     }
 
-    dcs->guest_domid = domid;
     dcs->sdss.dm.guest_domid = 0; /* means we haven't spawned */
 
     /* post-4.13 todo: move these next bits of defaulting to
@@ -1141,7 +1173,7 @@ static void initiate_domain_create(libxl__egc *egc,
     if (ret)
         goto error_out;
 
-    if (restore_fd >= 0 || dcs->domid_soft_reset != INVALID_DOMID) {
+    if (restore_fd >= 0 || dcs->domid_soft_reset != INVALID_DOMID || 
d_config->dm_restore_file) {
         LOGD(DEBUG, domid, "restoring, not running bootloader");
         domcreate_bootloader_done(egc, &dcs->bl, 0);
     } else  {
@@ -1217,7 +1249,16 @@ static void domcreate_bootloader_done(libxl__egc *egc,
     dcs->sdss.dm.callback = domcreate_devmodel_started;
     dcs->sdss.callback = domcreate_devmodel_started;
 
-    if (restore_fd < 0 && dcs->domid_soft_reset == INVALID_DOMID) {
+    if (restore_fd < 0 && dcs->domid_soft_reset == INVALID_DOMID && 
!d_config->dm_restore_file) {
+        rc = libxl__domain_build(gc, d_config, domid, state);
+        domcreate_rebuild_done(egc, dcs, rc);
+        return;
+    }
+
+    if ( d_config->dm_restore_file ) {
+        dcs->srs.dcs = dcs;
+        dcs->srs.ao = ao;
+        state->forked_vm = true;
         rc = libxl__domain_build(gc, d_config, domid, state);
         domcreate_rebuild_done(egc, dcs, rc);
         return;
@@ -1415,6 +1456,7 @@ static void domcreate_rebuild_done(libxl__egc *egc,
     /* convenience aliases */
     const uint32_t domid = dcs->guest_domid;
     libxl_domain_config *const d_config = dcs->guest_config;
+    libxl__domain_build_state *const state = &dcs->build_state;
 
     if (ret) {
         LOGD(ERROR, domid, "cannot (re-)build domain: %d", ret);
@@ -1422,6 +1464,9 @@ static void domcreate_rebuild_done(libxl__egc *egc,
         goto error_out;
     }
 
+    if ( d_config->dm_restore_file )
+        state->saved_state = GCSPRINTF("%s", d_config->dm_restore_file);
+
     store_libxl_entry(gc, domid, &d_config->b_info);
 
     libxl__multidev_begin(ao, &dcs->multidev);
@@ -1823,10 +1868,13 @@ static int do_domain_create(libxl_ctx *ctx, 
libxl_domain_config *d_config,
     GCNEW(cdcs);
     cdcs->dcs.ao = ao;
     cdcs->dcs.guest_config = d_config;
+    cdcs->dcs.guest_domid = *domid;
+
     libxl_domain_config_init(&cdcs->dcs.guest_config_saved);
     libxl_domain_config_copy(ctx, &cdcs->dcs.guest_config_saved, d_config);
     cdcs->dcs.restore_fd = cdcs->dcs.libxc_fd = restore_fd;
     cdcs->dcs.send_back_fd = send_back_fd;
+
     if (restore_fd > -1) {
         cdcs->dcs.restore_params = *params;
         rc = libxl__fd_flags_modify_save(gc, cdcs->dcs.restore_fd,
@@ -2069,6 +2117,43 @@ int libxl_domain_create_new(libxl_ctx *ctx, 
libxl_domain_config *d_config,
                             ao_how, aop_console_how);
 }
 
+int libxl_domain_fork_vm(libxl_ctx *ctx, uint32_t pdomid, uint32_t *domid)
+{
+    int rc;
+    struct xen_domctl_createdomain create = {0};
+    create.flags |= XEN_DOMCTL_CDF_hvm;
+    create.flags |= XEN_DOMCTL_CDF_hap;
+    create.flags |= XEN_DOMCTL_CDF_oos_off;
+    create.arch.emulation_flags = (XEN_X86_EMU_ALL & ~XEN_X86_EMU_VPCI);
+
+    create.ssidref = SECINITSID_DOMU;
+    create.max_vcpus = 1; // placeholder, will be cloned from pdomid
+    create.max_evtchn_port = 1023;
+    create.max_grant_frames = LIBXL_MAX_GRANT_FRAMES_DEFAULT;
+    create.max_maptrack_frames = LIBXL_MAX_MAPTRACK_FRAMES_DEFAULT;
+
+    if ( (rc = xc_domain_create(ctx->xch, domid, &create)) )
+        return rc;
+
+    if ( (rc = xc_memshr_fork(ctx->xch, pdomid, *domid)) )
+        xc_domain_destroy(ctx->xch, *domid);
+
+    return rc;
+}
+
+int libxl_domain_fork_launch_dm(libxl_ctx *ctx, libxl_domain_config *d_config,
+                                uint32_t domid,
+                                const libxl_asyncprogress_how *aop_console_how)
+{
+    unset_disk_colo_restore(d_config);
+    return do_domain_create(ctx, d_config, &domid, -1, -1, 0, 0, 
aop_console_how);
+}
+
+int libxl_domain_fork_reset(libxl_ctx *ctx, uint32_t domid)
+{
+    return xc_memshr_fork_reset(ctx->xch, domid);
+}
+
 int libxl_domain_create_restore(libxl_ctx *ctx, libxl_domain_config *d_config,
                                 uint32_t *domid, int restore_fd,
                                 int send_back_fd,
diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index dac1b8ddb8..a119e789a7 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -2784,7 +2784,7 @@ static void device_model_spawn_outcome(libxl__egc *egc,
 
     libxl__domain_build_state *state = dmss->build_state;
 
-    if (state->saved_state) {
+    if (state->saved_state && !state->forked_vm) {
         ret2 = unlink(state->saved_state);
         if (ret2) {
             LOGED(ERROR, dmss->guest_domid, "%s: failed to remove device-model 
state %s",
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index cdb294ab8d..95e6ecc9d3 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -392,9 +392,12 @@ int libxl__build_pre(libxl__gc *gc, uint32_t domid,
     libxl_domain_build_info *const info = &d_config->b_info;
     libxl_ctx *ctx = libxl__gc_owner(gc);
     char *xs_domid, *con_domid;
-    int rc;
+    int rc = 0;
     uint64_t size;
 
+    if ( state->forked_vm )
+        goto skip_fork;
+
     if (xc_domain_max_vcpus(ctx->xch, domid, info->max_vcpus) != 0) {
         LOG(ERROR, "Couldn't set max vcpu count");
         return ERROR_FAIL;
@@ -499,29 +502,6 @@ int libxl__build_pre(libxl__gc *gc, uint32_t domid,
         }
     }
 
-
-    rc = libxl__arch_extra_memory(gc, info, &size);
-    if (rc < 0) {
-        LOGE(ERROR, "Couldn't get arch extra constant memory size");
-        return ERROR_FAIL;
-    }
-
-    if (xc_domain_setmaxmem(ctx->xch, domid, info->target_memkb + size) < 0) {
-        LOGE(ERROR, "Couldn't set max memory");
-        return ERROR_FAIL;
-    }
-
-    xs_domid = xs_read(ctx->xsh, XBT_NULL, "/tool/xenstored/domid", NULL);
-    state->store_domid = xs_domid ? atoi(xs_domid) : 0;
-    free(xs_domid);
-
-    con_domid = xs_read(ctx->xsh, XBT_NULL, "/tool/xenconsoled/domid", NULL);
-    state->console_domid = con_domid ? atoi(con_domid) : 0;
-    free(con_domid);
-
-    state->store_port = xc_evtchn_alloc_unbound(ctx->xch, domid, 
state->store_domid);
-    state->console_port = xc_evtchn_alloc_unbound(ctx->xch, domid, 
state->console_domid);
-
     if (info->type != LIBXL_DOMAIN_TYPE_PV)
         hvm_set_conf_params(ctx->xch, domid, info);
 
@@ -556,8 +536,34 @@ int libxl__build_pre(libxl__gc *gc, uint32_t domid,
                          info->altp2m);
     }
 
+    rc = libxl__arch_extra_memory(gc, info, &size);
+    if (rc < 0) {
+        LOGE(ERROR, "Couldn't get arch extra constant memory size");
+        return ERROR_FAIL;
+    }
+
+    if (xc_domain_setmaxmem(ctx->xch, domid, info->target_memkb + size) < 0) {
+        LOGE(ERROR, "Couldn't set max memory");
+        return ERROR_FAIL;
+    }
+
     rc = libxl__arch_domain_create(gc, d_config, domid);
+    if ( rc )
+        goto out;
 
+skip_fork:
+    xs_domid = xs_read(ctx->xsh, XBT_NULL, "/tool/xenstored/domid", NULL);
+    state->store_domid = xs_domid ? atoi(xs_domid) : 0;
+    free(xs_domid);
+
+    con_domid = xs_read(ctx->xsh, XBT_NULL, "/tool/xenconsoled/domid", NULL);
+    state->console_domid = con_domid ? atoi(con_domid) : 0;
+    free(con_domid);
+
+    state->store_port = xc_evtchn_alloc_unbound(ctx->xch, domid, 
state->store_domid);
+    state->console_port = xc_evtchn_alloc_unbound(ctx->xch, domid, 
state->console_domid);
+
+out:
     return rc;
 }
 
@@ -615,6 +621,9 @@ int libxl__build_post(libxl__gc *gc, uint32_t domid,
     char **ents;
     int i, rc;
 
+    if ( state->forked_vm )
+        goto skip_fork;
+
     if (info->num_vnuma_nodes && !info->num_vcpu_soft_affinity) {
         rc = set_vnuma_affinity(gc, domid, info);
         if (rc)
@@ -639,6 +648,7 @@ int libxl__build_post(libxl__gc *gc, uint32_t domid,
         }
     }
 
+skip_fork:
     ents = libxl__calloc(gc, 12 + (info->max_vcpus * 2) + 2, sizeof(char *));
     ents[0] = "memory/static-max";
     ents[1] = GCSPRINTF("%"PRId64, info->max_memkb);
@@ -901,14 +911,16 @@ static int hvm_build_set_params(xc_interface *handle, 
uint32_t domid,
                                 libxl_domain_build_info *info,
                                 int store_evtchn, unsigned long *store_mfn,
                                 int console_evtchn, unsigned long *console_mfn,
-                                domid_t store_domid, domid_t console_domid)
+                                domid_t store_domid, domid_t console_domid,
+                                bool forked_vm)
 {
     struct hvm_info_table *va_hvm;
     uint8_t *va_map, sum;
     uint64_t str_mfn, cons_mfn;
     int i;
 
-    if (info->type == LIBXL_DOMAIN_TYPE_HVM) {
+    if ( info->type == LIBXL_DOMAIN_TYPE_HVM && !forked_vm )
+    {
         va_map = xc_map_foreign_range(handle, domid,
                                       XC_PAGE_SIZE, PROT_READ | PROT_WRITE,
                                       HVM_INFO_PFN);
@@ -1224,6 +1236,23 @@ int libxl__build_hvm(libxl__gc *gc, uint32_t domid,
     struct xc_dom_image *dom = NULL;
     bool device_model = info->type == LIBXL_DOMAIN_TYPE_HVM ? true : false;
 
+    if ( state->forked_vm )
+    {
+        rc = hvm_build_set_params(ctx->xch, domid, info, state->store_port,
+                                  &state->store_mfn, state->console_port,
+                                  &state->console_mfn, state->store_domid,
+                                  state->console_domid, state->forked_vm);
+
+        if ( rc )
+            return rc;
+
+        return xc_dom_gnttab_seed(ctx->xch, domid, true,
+                                  state->console_mfn,
+                                  state->store_mfn,
+                                  state->console_domid,
+                                  state->store_domid);
+    }
+
     xc_dom_loginit(ctx->xch);
 
     /*
@@ -1348,7 +1377,7 @@ int libxl__build_hvm(libxl__gc *gc, uint32_t domid,
     rc = hvm_build_set_params(ctx->xch, domid, info, state->store_port,
                                &state->store_mfn, state->console_port,
                                &state->console_mfn, state->store_domid,
-                               state->console_domid);
+                               state->console_domid, false);
     if (rc != 0) {
         LOG(ERROR, "hvm build set params failed");
         goto out;
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index b5adbfe4b7..ea6fe133a5 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1360,6 +1360,7 @@ typedef struct {
 
     char *saved_state;
     int dm_monitor_fd;
+    bool forked_vm;
 
     libxl__file_reference pv_kernel;
     libxl__file_reference pv_ramdisk;
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 7921950f6a..7c4c4057a9 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -956,6 +956,7 @@ libxl_domain_config = Struct("domain_config", [
     ("on_watchdog", libxl_action_on_shutdown),
     ("on_crash", libxl_action_on_shutdown),
     ("on_soft_reset", libxl_action_on_shutdown),
+    ("dm_restore_file", string, {'const': True}),
     ], dir=DIR_IN)
 
 libxl_diskinfo = Struct("diskinfo", [
diff --git a/tools/xl/xl.h b/tools/xl/xl.h
index 60bdad8ffb..9bdad6526e 100644
--- a/tools/xl/xl.h
+++ b/tools/xl/xl.h
@@ -31,6 +31,7 @@ struct cmd_spec {
 };
 
 struct domain_create {
+    uint32_t ddomid; /* fork launch dm for this domid */
     int debug;
     int daemonize;
     int monitor; /* handle guest reboots etc */
@@ -45,6 +46,7 @@ struct domain_create {
     const char *config_file;
     char *extra_config; /* extra config string */
     const char *restore_file;
+    const char *dm_restore_file;
     char *colo_proxy_script;
     bool userspace_colo_proxy;
     int migrate_fd; /* -1 means none */
@@ -127,6 +129,9 @@ int main_pciassignable_remove(int argc, char **argv);
 int main_pciassignable_list(int argc, char **argv);
 #ifndef LIBXL_HAVE_NO_SUSPEND_RESUME
 int main_restore(int argc, char **argv);
+int main_fork_vm(int argc, char **argv);
+int main_fork_launch_dm(int argc, char **argv);
+int main_fork_reset(int argc, char **argv);
 int main_migrate_receive(int argc, char **argv);
 int main_save(int argc, char **argv);
 int main_migrate(int argc, char **argv);
diff --git a/tools/xl/xl_cmdtable.c b/tools/xl/xl_cmdtable.c
index 5baa6023aa..94217e4ed4 100644
--- a/tools/xl/xl_cmdtable.c
+++ b/tools/xl/xl_cmdtable.c
@@ -180,6 +180,28 @@ struct cmd_spec cmd_table[] = {
       "-V, --vncviewer          Connect to the VNC display after the domain is 
created.\n"
       "-A, --vncviewer-autopass Pass VNC password to viewer via stdin."
     },
+    { "fork-vm",
+      &main_fork_vm, 0, 1,
+      "Fork a domain from the running parent domid",
+      "[options] <ParentDomid>",
+      "-h                       Print this help.\n"
+      "-d                       Enable debug messages.\n"
+    },
+    { "fork-launch-dm",
+      &main_fork_launch_dm, 0, 1,
+      "Launch the device model for a forked VM",
+      "[options] <ConfigFile> <DmRestoreFile> <Domid>",
+      "-h                       Print this help.\n"
+      "-p                       Do not unpause domain after restoring it.\n"
+      "-d                       Enable debug messages.\n"
+    },
+    { "fork-reset",
+      &main_fork_reset, 0, 1,
+      "Launch the device model for a forked VM",
+      "[options] <Domid>",
+      "-h                       Print this help.\n"
+      "-d                       Enable debug messages.\n"
+    },
     { "migrate-receive",
       &main_migrate_receive, 0, 1,
       "Restore a domain from a saved state",
diff --git a/tools/xl/xl_saverestore.c b/tools/xl/xl_saverestore.c
index 9be033fe65..c1dd74f33e 100644
--- a/tools/xl/xl_saverestore.c
+++ b/tools/xl/xl_saverestore.c
@@ -229,6 +229,102 @@ int main_restore(int argc, char **argv)
     return EXIT_SUCCESS;
 }
 
+int main_fork_vm(int argc, char **argv)
+{
+    int debug = 0;
+    uint32_t pdomid = 0, domid = INVALID_DOMID;
+    int opt;
+
+    SWITCH_FOREACH_OPT(opt, "d", NULL, "fork-vm", 1) {
+    case 'd':
+        debug = 1;
+        break;
+    }
+
+    if (argc-optind == 1) {
+        pdomid = atoi(argv[optind]);
+    } else {
+        help("fork-vm");
+        return EXIT_FAILURE;
+    }
+
+    if (libxl_domain_fork_vm(ctx, pdomid, &domid) || domid == INVALID_DOMID)
+        return EXIT_FAILURE;
+
+    fprintf(stderr, "VM fork created with domid: %u\n", domid);
+    return EXIT_SUCCESS;
+}
+
+int main_fork_launch_dm(int argc, char **argv)
+{
+    const char *config_file = NULL;
+    const char *dm_restore_file = NULL;
+    struct domain_create dom_info;
+    int paused = 0, debug = 0;
+    uint32_t ddomid = 0;
+    int opt, rc;
+
+    SWITCH_FOREACH_OPT(opt, "pd", NULL, "fork-launch-dm", 1) {
+    case 'p':
+        paused = 1;
+        break;
+    case 'd':
+        debug = 1;
+        break;
+    }
+
+    if (argc-optind == 3) {
+        config_file = argv[optind];
+        dm_restore_file = argv[optind + 1];
+        ddomid = atoi(argv[optind + 2]);
+    } else {
+        help("fork-launch-dm");
+        return EXIT_FAILURE;
+    }
+
+    memset(&dom_info, 0, sizeof(dom_info));
+    dom_info.ddomid = ddomid;
+    dom_info.dm_restore_file = dm_restore_file;
+    dom_info.debug = debug;
+    dom_info.paused = paused;
+    dom_info.config_file = config_file;
+    dom_info.migrate_fd = -1;
+    dom_info.send_back_fd = -1;
+
+    rc = create_domain(&dom_info);
+    if (rc < 0)
+        return EXIT_FAILURE;
+
+    return EXIT_SUCCESS;
+}
+
+int main_fork_reset(int argc, char **argv)
+{
+    int debug = 0;
+    uint32_t domid = 0;
+    int opt, rc;
+
+    SWITCH_FOREACH_OPT(opt, "d", NULL, "fork-reset", 1)
+    {
+    case 'd':
+        debug = 1;
+        break;
+    }
+
+    if (argc-optind == 1) {
+        domid = atoi(argv[optind]);
+    } else {
+        help("fork-reset");
+        return EXIT_FAILURE;
+    }
+
+    rc = libxl_domain_fork_reset(ctx, domid);
+    if (rc < 0)
+        return EXIT_FAILURE;
+
+    return EXIT_SUCCESS;
+}
+
 int main_save(int argc, char **argv)
 {
     uint32_t domid;
diff --git a/tools/xl/xl_vmcontrol.c b/tools/xl/xl_vmcontrol.c
index e520b1da79..d9cb19c599 100644
--- a/tools/xl/xl_vmcontrol.c
+++ b/tools/xl/xl_vmcontrol.c
@@ -645,6 +645,7 @@ int create_domain(struct domain_create *dom_info)
 
     libxl_domain_config d_config;
 
+    uint32_t ddomid = dom_info->ddomid; // launch dm for this domain iff set
     int debug = dom_info->debug;
     int daemonize = dom_info->daemonize;
     int monitor = dom_info->monitor;
@@ -655,6 +656,7 @@ int create_domain(struct domain_create *dom_info)
     const char *restore_file = dom_info->restore_file;
     const char *config_source = NULL;
     const char *restore_source = NULL;
+    const char *dm_restore_file = dom_info->dm_restore_file;
     int migrate_fd = dom_info->migrate_fd;
     bool config_in_json;
 
@@ -923,6 +925,12 @@ start:
          * restore/migrate-receive it again.
          */
         restoring = 0;
+    } else if ( ddomid ) {
+        d_config.dm_restore_file = dm_restore_file;
+        ret = libxl_domain_fork_launch_dm(ctx, &d_config, ddomid,
+                                          autoconnect_console_how);
+        domid = ddomid;
+        ddomid = INVALID_DOMID;
     } else if (domid_soft_reset != INVALID_DOMID) {
         /* Do soft reset. */
         ret = libxl_domain_soft_reset(ctx, &d_config, domid_soft_reset,
-- 
2.20.1


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