Add support for xl devd to support 9pfs in a domU.  devd need to spawn a
pvqemu for the domain to service 9pfs as well as qdisk backends.  Rename
num_qdisks to pvqemu_refcnt to be more generic.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
---
 tools/libs/light/libxl_device.c   | 22 ++++++++++++----------
 tools/libs/light/libxl_dm.c       | 11 ++++++-----
 tools/libs/light/libxl_internal.h |  4 ++--
 3 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/tools/libs/light/libxl_device.c b/tools/libs/light/libxl_device.c
index ae2b71b0bf..eb76d3a486 100644
--- a/tools/libs/light/libxl_device.c
+++ b/tools/libs/light/libxl_device.c
@@ -1517,12 +1517,12 @@ static void device_complete(libxl__egc *egc, libxl__ao_device *aodev)
     libxl__nested_ao_free(aodev->ao);
 }
 
-static void qdisk_spawn_outcome(libxl__egc *egc, libxl__dm_spawn_state *dmss,
-                                int rc)
+static void qemu_xenpv_spawn_outcome(libxl__egc *egc,
+                                     libxl__dm_spawn_state *dmss, int rc)
 {
     STATE_AO_GC(dmss->spawn.ao);
 
-    LOGD(DEBUG, dmss->guest_domid, "qdisk backend spawn %s",
+    LOGD(DEBUG, dmss->guest_domid, "qemu xenpv backend spawn %s",
                 rc ? "failed" : "succeed");
 
     libxl__nested_ao_free(dmss->spawn.ao);
@@ -1545,7 +1545,7 @@ typedef struct libxl__ddomain_device {
  */
 typedef struct libxl__ddomain_guest {
     uint32_t domid;
-    int num_qdisks;
+    int pvqemu_refcnt;
     XEN_SLIST_HEAD(, struct libxl__ddomain_device) devices;
     XEN_SLIST_ENTRY(struct libxl__ddomain_guest) next;
 } libxl__ddomain_guest;
@@ -1639,15 +1639,16 @@ static int add_device(libxl__egc *egc, libxl__ao *ao,
 
     switch(dev->backend_kind) {
     case LIBXL__DEVICE_KIND_QDISK:
-        if (dguest->num_qdisks == 0) {
+    case LIBXL__DEVICE_KIND_9PFS:
+        if (dguest->pvqemu_refcnt == 0) {
             GCNEW(dmss);
             dmss->guest_domid = dev->domid;
             dmss->spawn.ao = ao;
-            dmss->callback = qdisk_spawn_outcome;
+            dmss->callback = qemu_xenpv_spawn_outcome;
 
-            libxl__spawn_qdisk_backend(egc, dmss);
+            libxl__spawn_qemu_xenpv_backend(egc, dmss);
         }
-        dguest->num_qdisks++;
+        dguest->pvqemu_refcnt++;
         break;
     default:
         GCNEW(aodev);
@@ -1678,8 +1679,9 @@ static int remove_device(libxl__egc *egc, libxl__ao *ao,
 
     switch(ddev->dev->backend_kind) {
     case LIBXL__DEVICE_KIND_QDISK:
-        if (--dguest->num_qdisks == 0) {
-            rc = libxl__destroy_qdisk_backend(gc, dev->domid);
+    case LIBXL__DEVICE_KIND_9PFS:
+        if (--dguest->pvqemu_refcnt == 0) {
+            rc = libxl__destroy_qemu_xenpv_backend(gc, dev->domid);
             if (rc)
                 goto out;
         }
diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
index 6ef16ad2a0..5343ebd4dc 100644
--- a/tools/libs/light/libxl_dm.c
+++ b/tools/libs/light/libxl_dm.c
@@ -3370,7 +3370,8 @@ static void device_model_postconfig_done(libxl__egc *egc,
     dmss->callback(egc, dmss, rc);
 }
 
-void libxl__spawn_qdisk_backend(libxl__egc *egc, libxl__dm_spawn_state *dmss)
+void libxl__spawn_qemu_xenpv_backend(libxl__egc *egc,
+                                     libxl__dm_spawn_state *dmss)
 {
     STATE_AO_GC(dmss->spawn.ao);
     flexarray_t *dm_args, *dm_envs;
@@ -3403,7 +3404,7 @@ void libxl__spawn_qdisk_backend(libxl__egc *egc, libxl__dm_spawn_state *dmss)
     libxl__set_qemu_env_for_xsa_180(gc, dm_envs);
     envs = (char **) flexarray_contents(dm_envs);
 
-    logfile_w = libxl__create_qemu_logfile(gc, GCSPRINTF("qdisk-%u", domid));
+    logfile_w = libxl__create_qemu_logfile(gc, GCSPRINTF("qemu-xenpv-%u", domid));
     if (logfile_w < 0) {
         rc = logfile_w;
         goto out;
@@ -3430,7 +3431,7 @@ void libxl__spawn_qdisk_backend(libxl__egc *egc, libxl__dm_spawn_state *dmss)
      * because we will call this from unprivileged driver domains,
      * so save it in the current domain libxl private dir.
      */
-    dmss->spawn.pidpath = GCSPRINTF("libxl/%u/qdisk-backend-pid", domid);
+    dmss->spawn.pidpath = GCSPRINTF("libxl/%u/qemu-xenpv-backend-pid", domid);
     dmss->spawn.midproc_cb = libxl__spawn_record_pid;
     dmss->spawn.confirm_cb = device_model_confirm;
     dmss->spawn.failure_cb = device_model_startup_failed;
@@ -3460,12 +3461,12 @@ static int kill_device_model(libxl__gc *gc, const char *xs_path_pid)
 }
 
 /* Helper to destroy a Qdisk backend */
-int libxl__destroy_qdisk_backend(libxl__gc *gc, uint32_t domid)
+int libxl__destroy_qemu_xenpv_backend(libxl__gc *gc, uint32_t domid)
 {
     char *pid_path;
     int rc;
 
-    pid_path = GCSPRINTF("libxl/%u/qdisk-backend-pid", domid);
+    pid_path = GCSPRINTF("libxl/%u/qemu-xenpv-backend-pid", domid);
 
     rc = kill_device_model(gc, pid_path);
     if (rc)
diff --git a/tools/libs/light/libxl_internal.h b/tools/libs/light/libxl_internal.h
index d5732d1c37..b9e4661129 100644
--- a/tools/libs/light/libxl_internal.h
+++ b/tools/libs/light/libxl_internal.h
@@ -4195,9 +4195,9 @@ _hidden char *libxl__stub_dm_name(libxl__gc *gc, const char * guest_name);
 
 /* Qdisk backend launch helpers */
 
-_hidden void libxl__spawn_qdisk_backend(libxl__egc *egc,
+_hidden void libxl__spawn_qemu_xenpv_backend(libxl__egc *egc,
                                         libxl__dm_spawn_state *dmss);
-_hidden int libxl__destroy_qdisk_backend(libxl__gc *gc, uint32_t domid);
+_hidden int libxl__destroy_qemu_xenpv_backend(libxl__gc *gc, uint32_t domid);
 
 /*----- Domain creation -----*/
 
-- 
2.43.0

On Tue, Jan 09, 2024 at 12:05:40PM -0500, Jason Andryuk wrote:
> @@ -3430,7 +3431,7 @@ void libxl__spawn_qdisk_backend(libxl__egc *egc, libxl__dm_spawn_state *dmss)
>       * because we will call this from unprivileged driver domains,
>       * so save it in the current domain libxl private dir.
>       */
> -    dmss->spawn.pidpath = GCSPRINTF("libxl/%u/qdisk-backend-pid", domid);
> +    dmss->spawn.pidpath = GCSPRINTF("libxl/%u/qemu-xenpv-backend-pid", domid);

This path is documented in "docs/misc/xenstore-paths.pandoc", I'm not
sure it's such a good idea to change it.

But maybe it's ok to change the path because xl devd is expected add
then remove this path? And that pid isn't going to be useful to anything
else?

I'd rather not change the path, but if you still think it's ok, we can
go for it. Thought?

Thanks,

-- 
Anthony PERARD

On Wed, Feb 28, 2024 at 11:01 AM Anthony PERARD
<anthony.perard@cloud.com> wrote:
>
> On Tue, Jan 09, 2024 at 12:05:40PM -0500, Jason Andryuk wrote:
> > @@ -3430,7 +3431,7 @@ void libxl__spawn_qdisk_backend(libxl__egc *egc, libxl__dm_spawn_state *dmss)
> >       * because we will call this from unprivileged driver domains,
> >       * so save it in the current domain libxl private dir.
> >       */
> > -    dmss->spawn.pidpath = GCSPRINTF("libxl/%u/qdisk-backend-pid", domid);
> > +    dmss->spawn.pidpath = GCSPRINTF("libxl/%u/qemu-xenpv-backend-pid", domid);
>
> This path is documented in "docs/misc/xenstore-paths.pandoc", I'm not
> sure it's such a good idea to change it.
>
> But maybe it's ok to change the path because xl devd is expected add
> then remove this path? And that pid isn't going to be useful to anything
> else?
>
> I'd rather not change the path, but if you still think it's ok, we can
> go for it. Thought?

I changed the path to keep it consistent with the internal libxl
names.  The node is for libxl's internal use, so it seemed okay to
change.  But it is externally visible, so there could be other
software looking at it.  I'm fine with leaving the xenstore name
unchanged.

(I didn't want to rename all the qdisk stuff, but it seemed like it
should be renamed since it would also handle 9pfs.)

Thanks,
Jason