[Xen-devel] [PATCH V2] 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. Blkfront before 2.6.26 relies on this behaviour otherwise guest
cannot boot when running in 32-on-64 mode. Blkfront after 2.6.26 writes that
node itself, in which case it's just an overwrite to an existing node which
should be OK.

In fact Xend writes the ABI for all frontends including console and vif. But
nowadays only old disk frontends rely on that behaviour so that we only write
the ABI for disk frontends in libxl, minimizing the impact.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>
Cc: Valtteri Kiviniemi <kiviniemi.valtteri@xxxxxxxxx>
---
 tools/libxc/xc_dom_arm.c |   13 +++++++++++++
 tools/libxc/xc_dom_x86.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
 tools/libxc/xenctrl.h    |   12 ++++++++++++
 tools/libxl/libxl.c      |   25 +++++++++++++++++++++++++
 4 files changed, 94 insertions(+)

diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
index 041832e..acdac9e 100644
--- a/tools/libxc/xc_dom_arm.c
+++ b/tools/libxc/xc_dom_arm.c
@@ -29,6 +29,19 @@
 #define CONSOLE_PFN_OFFSET 0
 #define XENSTORE_PFN_OFFSET 1
 
+/* get guest IO ABI */
+int xc_domain_get_native_protocol(xc_interface *xch,
+                                  uint32_t domid,
+                                  char **guest_abi);
+{
+    *guest_abi = strdup(XEN_IO_PROTO_ABI_ARM);
+
+    if ( *guest_abi == NULL )
+        return -ENOMEM;
+
+    return 0;
+}
+
 /* ------------------------------------------------------------------------ */
 /*
  * arm guests are hybrid and start off with paging disabled, therefore no
diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index eb9ac07..3745d54 100644
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -47,6 +47,50 @@
 #define round_down(addr, mask)   ((addr) & ~(mask))
 #define round_up(addr, mask)     ((addr) | (mask))
 
+/* get guest IO ABI */
+int xc_domain_get_native_protocol(xc_interface *xch,
+                                  uint32_t domid,
+                                  char **guest_abi)
+{
+    int ret;
+    uint32_t guest_width;
+    const char *protocol = NULL;
+    DECLARE_DOMCTL;
+
+    *guest_abi = NULL;
+
+    memset(&domctl, 0, sizeof(domctl));
+    domctl.domain = domid;
+    domctl.cmd = XEN_DOMCTL_get_address_size;
+
+    ret = do_domctl(xch, &domctl);
+
+    if ( ret )
+        goto out;
+
+    guest_width = domctl.u.address_size.size;
+
+    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:
+        ret = -EINVAL;
+        goto out;
+    }
+
+    *guest_abi = strdup(protocol);
+
+    if ( *guest_abi == NULL )
+        ret = -ENOMEM;
+
+ out:
+    return ret;
+}
+
 static unsigned long
 nr_page_tables(struct xc_dom_image *dom,
                xen_vaddr_t start, xen_vaddr_t end, unsigned long bits)
diff --git a/tools/libxc/xenctrl.h b/tools/libxc/xenctrl.h
index 50853af..83cca1f 100644
--- a/tools/libxc/xenctrl.h
+++ b/tools/libxc/xenctrl.h
@@ -637,6 +637,18 @@ int xc_domain_hvm_setcontext(xc_interface *xch,
                              uint32_t size);
 
 /**
+ * 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_abi guest's navtive IO ABI string
+ * @return 0 on success, -ev on failure
+ */
+int xc_domain_get_native_protocol(xc_interface *xch,
+                                  uint32_t domid,
+                                  char **guest_abi);
+
+/**
  * 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..3f6afad 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2037,6 +2037,13 @@ static void device_disk_add(libxl__egc *egc, uint32_t 
domid,
     int rc;
     libxl_ctx *ctx = gc->owner;
     xs_transaction_t t = XBT_NULL;
+    char *protocol = NULL;
+
+    libxl_domain_type type = libxl__domain_type(gc, domid);
+    if (type == LIBXL_DOMAIN_TYPE_INVALID) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
 
     for (;;) {
         rc = libxl__xs_transaction_start(gc, &t);
@@ -2156,10 +2163,28 @@ 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. Xend does this, port
+         * this behaviour to xl.
+         *
+         * New kernels write this node themselves. In that case it just
+         * overwrites an existing node which is OK.
+         */
+        if (type == LIBXL_DOMAIN_TYPE_PV) {
+            if (!xc_domain_get_native_protocol(ctx->xch, domid, &protocol)) {
+                flexarray_append(front, "protocol");
+                flexarray_append(front, 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));
 
+        if (protocol)
+            free(protocol);
+
         rc = libxl__xs_transaction_commit(gc, &t);
         if (!rc) break;
         if (rc < 0) goto out;
-- 
1.7.10.4


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