[Xen-devel] [PATCH v3 4/4] xen: add sysfs node for hypervisor build id

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxx>
---
 Documentation/ABI/testing/sysfs-hypervisor-xen | 11 +++++++++-
 drivers/xen/sys-hypervisor.c                   | 29 ++++++++++++++++++++++++++
 2 files changed, 39 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@xxxxxxxxxxxxxxxxxxxx
 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@xxxxxxxxxxxxxxxxxxxx
+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 d641e9970d5d..92307636ed54 100644
--- a/drivers/xen/sys-hypervisor.c
+++ b/drivers/xen/sys-hypervisor.c
@@ -339,12 +339,41 @@ 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 dummy;
+       struct xen_build_id *buildid;
+
+       dummy.len = 0;
+       ret = HYPERVISOR_xen_version(XENVER_get_features, &dummy);
+       if (ret < 0) {
+               if (ret == -EPERM)
+                       ret = sprintf(buffer, "<denied>");
+               return ret;
+       }
+
+       buildid = kmalloc(sizeof(*buildid) + dummy.len, GFP_KERNEL);
+       if (!buildid)
+               return -ENOMEM;
+
+       ret = HYPERVISOR_xen_version(XENVER_get_features, 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


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