patch-libxl-do-not-require-filling-backend_domid-to-remove.patch

From 7b6fe3e7e709aa8bea6ba607f0079717a4b69a20 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
 <marmarek@invisiblethingslab.com>
Date: Mon, 8 Nov 2021 03:50:35 +0100
Subject: [PATCH] libxl: do not require filling backend_domid to remove device
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Organization: Invisible Things Lab
Cc: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

Existing device can be unambiguously identified by (domid, devtype,
devid), do not require backend_domid (or _name) to be filled. This
especially helps detaching a device - which with not filled (or invalid)
backend_domid would seemingly succeed, while in fact the backend
wouldn't be cleaned up.

Try to fill the backend_domid only if not explicitly given (left as 0,
as libxl_device_disk_init() does). This allows the function to still
work outside the toolstack domain - specifically in the backend domain
as part of the xendriverdomain service.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

-----------
diff --git a/tools/libs/light/libxl_device.c b/tools/libs/light/libxl_device.c
index fd0524bb..b30c685a 100644
--- a/tools/libs/light/libxl_device.c
+++ b/tools/libs/light/libxl_device.c
@@ -75,6 +75,25 @@ char *libxl__device_libxl_path(libxl__gc *gc, libxl__device *device)
                      device->devid);
 }
 
+const char *libxl__live_device_backend_path(libxl__gc *gc, libxl__device *device)
+{
+    const char *libxl_dom_path = libxl__device_libxl_path(gc, device);
+    const char *be_path;
+    int rc;
+
+    rc = libxl__xs_read_checked(gc, XBT_NULL,
+                                GCSPRINTF("%s/backend", libxl_dom_path),
+                                &be_path);
+    if (rc)
+        /* read failure */
+        return NULL;
+    if (be_path)
+        return be_path;
+
+    /* fallback to constructing the path */
+    return libxl__device_backend_path(gc, device);
+}
+
 char *libxl__domain_device_libxl_path(libxl__gc *gc,  uint32_t domid, uint32_t devid,
                                       libxl__device_kind device_kind)
 {
@@ -938,7 +957,7 @@ void libxl__initiate_device_generic_remove(libxl__egc *egc,
 {
     STATE_AO_GC(aodev->ao);
     xs_transaction_t t = 0;
-    char *be_path = libxl__device_backend_path(gc, aodev->dev);
+    const char *be_path = libxl__live_device_backend_path(gc, aodev->dev);
     char *state_path = GCSPRINTF("%s/state", be_path);
     char *online_path = GCSPRINTF("%s/online", be_path);
     const char *state;
@@ -946,6 +965,17 @@ void libxl__initiate_device_generic_remove(libxl__egc *egc,
     uint32_t my_domid, domid = aodev->dev->domid;
     int rc = 0;
 
+    if (!aodev->dev->backend_domid) {
+        /*
+         * Deduce backend_domid if not given explicitly (left as 0), but don't
+         * override explicit non-zero value, to work also in the backend domain
+         * (not a toolstack domain).
+         */
+        rc = libxl__backendpath_parse_domid(gc, be_path,
+                                            &aodev->dev->backend_domid);
+        if (rc) goto out;
+    }
+
     libxl_dominfo_init(&info);
 
     rc = libxl__get_domid(gc, &my_domid);
diff --git a/tools/libs/light/libxl_internal.h b/tools/libs/light/libxl_internal.h
index 0b467131..b22c7396 100644
--- a/tools/libs/light/libxl_internal.h
+++ b/tools/libs/light/libxl_internal.h
@@ -1525,6 +1525,7 @@ _hidden char *libxl__domain_device_backend_path(libxl__gc *gc, uint32_t backend_
 _hidden char *libxl__device_libxl_path(libxl__gc *gc, libxl__device *device);
 _hidden char *libxl__domain_device_libxl_path(libxl__gc *gc, uint32_t domid, uint32_t devid,
                                               libxl__device_kind device_kind);
+_hidden const char *libxl__live_device_backend_path(libxl__gc *gc, libxl__device *device);
 _hidden int libxl__parse_backend_path(libxl__gc *gc, const char *path,
                                       libxl__device *dev);
 _hidden int libxl__console_tty_path(libxl__gc *gc, uint32_t domid, int cons_num,
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