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Re: [Xen-devel] [PATCH] /sys/hypervisor/uuid

To: Markus Armbruster <armbru@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] /sys/hypervisor/uuid
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Fri, 19 May 2006 01:57:44 -0500
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
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Markus Armbruster wrote:
New /sys/hypervisor/uuid, containing this domain's UUID.

Stripping off /vm/ from the value of vm to get the UUID isn't exactly
nice.  The alternative is to add a XENVER_get_uuid code to
HYPERVISOR_xen_version(), but I'm not sure that's worth it.

Signed-off-by: Markus Armbruster <armbru@xxxxxxxxxx>

I really don't think we should be mirroring things in sysfs that are available in userspace. What benefit is there of having two interfaces to the same information?

If the argument is that we don't want to rely on libxenstore in a domU, then we should be exposing all of XenStore in sysfs.

The uuid parameter is a construction of Xend. Xend is *not* a part of the supported guest interface. By exposing the uuid in the kernel interface, you're tying an unsupported interface to what really should be a supported interface.

Plus, there's already a patch floating on LKML for a /sys/hypervisor. We shouldn't start adding attributes to this namespace as it could potentially conflict with the existing patch.

In the very least, we ought to stick this stuff in /sys/hypervisor/xen.


Anthony Liguori

diff -r ddba92a5cba9 drivers/xen/core/xen_sysfs.c
--- a/drivers/xen/core/xen_sysfs.c      Tue May 09 12:41:38 2006 +0200
+++ b/drivers/xen/core/xen_sysfs.c      Thu May 18 18:06:35 2006 +0200
@@ -8,12 +8,14 @@
#include <linux/config.h>
+#include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <asm/hypervisor.h>
 #include <xen/features.h>
 #include <xen/hypervisor_sysfs.h>
+#include <xen/xenbus.h>
 MODULE_AUTHOR("Mike D. Day <ncmike@xxxxxxxxxx>");
@@ -92,6 +94,37 @@ static void xen_sysfs_version_destroy(vo
 static void xen_sysfs_version_destroy(void)
        sysfs_remove_group(&hypervisor_subsys.kset.kobj, &version_group);
+/* UUID */
+static ssize_t uuid_show(struct hyp_sysfs_attr *attr, char *buffer)
+       char *val;
+       int ret;
+       val = xenbus_read(XBT_NULL, "vm", "", NULL);
+       if (IS_ERR(val))
+               ret = PTR_ERR(val);
+       else if (strncmp(val, "/vm/", 4))
+               ret = -EIO;
+       else
+               ret = sprintf(buffer, "%s\n", val + 4);
+       kfree(val);
+       return ret;
+static int __init xen_sysfs_uuid_init(void)
+       return sysfs_create_file(&hypervisor_subsys.kset.kobj, &uuid_attr.attr);
+static void xen_sysfs_uuid_destroy(void)
+       sysfs_remove_file(&hypervisor_subsys.kset.kobj, &uuid_attr.attr);
/* xen compilation attributes */
@@ -285,10 +318,15 @@ static int __init hyper_sysfs_init(void)
        ret = xen_compilation_init();
        if (ret)
                goto comp_out;
+       ret = xen_sysfs_uuid_init();
+       if (ret)
+               goto uuid_out;
        ret = xen_properties_init();
        if (!ret)
                goto out;
+ xen_sysfs_uuid_destroy();
@@ -302,6 +340,7 @@ static void hyper_sysfs_exit(void)
+       xen_sysfs_uuid_destroy();
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