[PATCH v4 4/4] xen: add sysfs node for hypervisor build id

[Juergen Gross <jgross@suse.com>]

For support of Xen hypervisor live patching the hypervisor build id is
needed. Add a node /sys/hypervisor/properties/buildid containing the
information.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V4:
  - send correct patch
---
 Documentation/ABI/testing/sysfs-hypervisor-xen | 11 +++++++++-
 drivers/xen/sys-hypervisor.c                   | 28 ++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-hypervisor-xen b/Documentation/ABI/testing/sysfs-hypervisor-xen
index c0edb3fdd6eb..53b7b2ea7515 100644
--- a/Documentation/ABI/testing/sysfs-hypervisor-xen
+++ b/Documentation/ABI/testing/sysfs-hypervisor-xen
@@ -1,5 +1,5 @@
 What:		/sys/hypervisor/guest_type
-Date:		May 2017
+Date:		June 2017
 KernelVersion:	4.13
 Contact:	xen-devel@lists.xenproject.org
 Description:	If running under Xen:
@@ -32,3 +32,12 @@ Description:	If running under Xen:
 		Describes Xen PMU features (as an integer). A set bit indicates
 		that the corresponding feature is enabled. See
 		include/xen/interface/xenpmu.h for available features
+
+What:		/sys/hypervisor/properties/buildid
+Date:		June 2017
+KernelVersion:	4.13
+Contact:	xen-devel@lists.xenproject.org
+Description:	If running under Xen:
+		Build id of the hypervisor, needed for hypervisor live patching.
+		Might return "<denied>" in case of special security settings
+		in the hypervisor.
diff --git a/drivers/xen/sys-hypervisor.c b/drivers/xen/sys-hypervisor.c
index 10400917e8e8..f8eeed46fbc3 100644
--- a/drivers/xen/sys-hypervisor.c
+++ b/drivers/xen/sys-hypervisor.c
@@ -353,12 +353,40 @@ static ssize_t features_show(struct hyp_sysfs_attr *attr, char *buffer)
 
 HYPERVISOR_ATTR_RO(features);
 
+static ssize_t buildid_show(struct hyp_sysfs_attr *attr, char *buffer)
+{
+	ssize_t ret;
+	struct xen_build_id *buildid;
+
+	ret = HYPERVISOR_xen_version(XENVER_build_id, NULL);
+	if (ret < 0) {
+		if (ret == -EPERM)
+			ret = sprintf(buffer, "<denied>");
+		return ret;
+	}
+
+	buildid = kmalloc(sizeof(*buildid) + ret, GFP_KERNEL);
+	if (!buildid)
+		return -ENOMEM;
+
+	buildid->len = ret;
+	ret = HYPERVISOR_xen_version(XENVER_build_id, buildid);
+	if (ret > 0)
+		ret = sprintf(buffer, "%s", buildid->buf);
+	kfree(buildid);
+
+	return ret;
+}
+
+HYPERVISOR_ATTR_RO(buildid);
+
 static struct attribute *xen_properties_attrs[] = {
 	&capabilities_attr.attr,
 	&changeset_attr.attr,
 	&virtual_start_attr.attr,
 	&pagesize_attr.attr,
 	&features_attr.attr,
+	&buildid_attr.attr,
 	NULL
 };
 
-- 
2.12.3