[Xen-devel] [PATCH] libxl: write IO ABI for disk frontends

[Wei Liu <wei.liu2@xxxxxxxxxx>]

This is a patch to forward-port a Xend behaviour. Xend writes IO ABI used for
all frontends. Linux kernel before 2.6.26 relies on this behaviour otherwise
it cannot boot. Blkfront after 2.6.26 writes that node itself, in which case
it's just an overwrite of the existing node which should be OK.

In fact Xend writes the ABI for all frontends including console and vif. But
nowadays it seems only old disk frontends rely on that ABI node so that we
only write the ABI for disk frontends in libxl, minimizing the impact. Also
ARM guests should not have this problem because they have new disk frontend so
the snippets of this workaround are compiled for X86 target only.

Also cleaned up trailing whitespaces while I was there.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxc/xc_domain.c     |   20 ++++++++++++++++++
 tools/libxc/xenctrl.h       |   14 +++++++++++++
 tools/libxl/libxl.c         |   12 +++++++++++
 tools/libxl/libxl_create.c  |   49 +++++++++++++++++++++++++++++++++++++++++++
 tools/libxl/libxl_types.idl |    7 ++++---
 5 files changed, 99 insertions(+), 3 deletions(-)

diff --git a/tools/libxc/xc_domain.c b/tools/libxc/xc_domain.c
index 480ce91..c3d8e28 100644
--- a/tools/libxc/xc_domain.c
+++ b/tools/libxc/xc_domain.c
@@ -379,6 +379,26 @@ int xc_domain_hvm_setcontext(xc_interface *xch,
     return ret;
 }
 
+#if defined (__i386__) || (__x86_64__)
+/* get guest word width */
+int xc_domain_getwidth(xc_interface *xch,
+                       uint32_t domid,
+                       uint32_t *guest_width)
+{
+    int ret;
+    DECLARE_DOMCTL;
+
+    domctl.domain = domid;
+    domctl.cmd = XEN_DOMCTL_get_address_size;
+
+    ret = do_domctl(xch, &domctl);
+
+    *guest_width = domctl.u.address_size.size;
+
+    return ret;
+}
+#endif
+
 int xc_vcpu_getcontext(xc_interface *xch,
                        uint32_t domid,
                        uint32_t vcpu,
diff --git a/tools/libxc/xenctrl.h b/tools/libxc/xenctrl.h
index 50853af..c02dc1f 100644
--- a/tools/libxc/xenctrl.h
+++ b/tools/libxc/xenctrl.h
@@ -636,6 +636,20 @@ int xc_domain_hvm_setcontext(xc_interface *xch,
                              uint8_t *hvm_ctxt,
                              uint32_t size);
 
+#if defined (__i386__) || (__x86_64__)
+/**
+ * This function will return the guest word width
+ *
+ * @parm xch a handle to an open hypervisor interface
+ * @parm domid the domain to get address width for
+ * @parm guest_width word width for guest
+ * @return 0 on success, -ev on failure
+ */
+int xc_domain_getwidth(xc_interface *xch,
+                       uint32_t domid,
+                       uint32_t *guest_width);
+#endif
+
 /**
  * This function returns information about the execution context of a
  * particular vcpu of a domain.
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 572c2c6..5b8c9dc 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2156,6 +2156,18 @@ static void device_disk_add(libxl__egc *egc, uint32_t 
domid,
         flexarray_append(front, "device-type");
         flexarray_append(front, disk->is_cdrom ? "cdrom" : "disk");
 
+        /*
+         * Old PV kernels before 2.6.26 rely on tool stack to write disk native
+         * protocol to frontend node.
+         *
+         * New kernels write this node themselves. In that case it just
+         * overwrites an existing node which is OK.
+         */
+        if (disk->native_protocol) {
+            flexarray_append(front, "protocol");
+            flexarray_append(front, disk->native_protocol);
+        }
+
         libxl__device_generic_add(gc, t, device,
                             libxl__xs_kvs_of_flexarray(gc, back, back->count),
                             libxl__xs_kvs_of_flexarray(gc, front, 
front->count));
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 30a4507..7abcaf9 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -23,6 +23,7 @@
 #include <xc_dom.h>
 #include <xenguest.h>
 #include <xen/hvm/hvm_info_table.h>
+#include <xen/io/protocols.h>
 
 int libxl__domain_create_info_setdefault(libxl__gc *gc,
                                          libxl_domain_create_info *c_info)
@@ -910,6 +911,54 @@ static void domcreate_rebuild_done(libxl__egc *egc,
         goto error_out;
     }
 
+#if defined (__i386__) || (__x86_64__)
+    /*
+     * Pass along the disk navtive protocol to disks so that the protocol can
+     * be written to frontend Xenstore node. This is a workaround for old PV
+     * kernels before 2.6.26.
+     *
+     * Newer blkfront will write that node itself. In that case frontend just
+     * rewrites the node as it sees fit.
+     *
+     * Note that Xend actually propagate this vaule to all frontends including
+     * console and vifs. As now this is only needed for disk frontend so here
+     * we minimize the impact.
+     *
+     * Presumably ARM guests don't have this problem, so this snippet is only
+     * compiled for X86 target.
+     */
+
+    if (d_config->c_info.type == LIBXL_DOMAIN_TYPE_PV) {
+        int i;
+        uint32_t guest_width;
+        const char *protocol = NULL;
+
+        ret = xc_domain_getwidth(CTX->xch, domid, &guest_width);
+        if (ret) {
+            ret = ERROR_FAIL;
+            goto error_out;
+        }
+
+        switch (guest_width) {
+        case 32: /* 32 bit guest */
+            protocol = XEN_IO_PROTO_ABI_X86_32;
+            break;
+        case 64: /* 64 bit guest */
+            protocol = XEN_IO_PROTO_ABI_X86_64;
+            break;
+        default:
+            LIBXL__LOG(ctx, LIBXL__LOG_ERROR,
+                       "invalid address size for domain: %u",
+                       guest_width);
+            ret = ERROR_FAIL;
+            goto error_out;
+        }
+
+        for (i = 0; i < d_config->num_disks; i++)
+            d_config->disks[i].native_protocol = strdup(protocol);
+    }
+#endif
+
     store_libxl_entry(gc, domid, &d_config->b_info);
 
     libxl__multidev_begin(ao, &dcs->multidev);
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 6cb6de6..22622a9 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -274,7 +274,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
     ("disable_migrate", libxl_defbool),
     ("cpuid",           libxl_cpuid_policy_list),
     ("blkdev_start",    string),
-    
+
     ("device_model_version", libxl_device_model_version),
     ("device_model_stubdomain", libxl_defbool),
     # if you set device_model you must set device_model_version too
@@ -318,9 +318,9 @@ libxl_domain_build_info = Struct("domain_build_info",[
                                        ("keymap",           string),
                                        ("sdl",              libxl_sdl_info),
                                        ("spice",            libxl_spice_info),
-                                       
+
                                        ("gfx_passthru",     libxl_defbool),
-                                       
+
                                        ("serial",           string),
                                        ("boot",             string),
                                        ("usb",              libxl_defbool),
@@ -371,6 +371,7 @@ libxl_device_disk = Struct("device_disk", [
     ("removable", integer),
     ("readwrite", integer),
     ("is_cdrom", integer),
+    ("native_protocol", string),
     ])
 
 libxl_device_nic = Struct("device_nic", [
-- 
1.7.10.4


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