linux-kernel - Re: [PATCH] afs: correctly use 64-bit time for UUID

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Date:   Wed, 11 Jan 2017 16:55:58 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     David Howells <dhowells@...hat.com>
Cc:     Tina Ruchandani <ruchandani.tina@...il.com>,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] afs: correctly use 64-bit time for UUID

On Wednesday, January 11, 2017 2:47:20 PM CET David Howells wrote:
> Arnd Bergmann <arnd@...db.de> wrote:
> 
> > > Is it worth abstracting out in-kernel UUID generation?
> > 
> > Do you mean moving it out of AFS into lib/*.c? I think the 'afs_uuid'
> > structure is quite different from other UUID definitions, so that wouldn't
> > work.
> 
> afs_uuid is as it is to make it easier to package into the on-wire format, but
> I suspect there's no problem with using a completely random UUID instead and
> divvying it up the same way.

Maybe like this:

8<----7
>From 9e164f852366750fdd732ae317af9f4a9a04a16e Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@...db.de>
Date: Wed, 11 Jan 2017 16:53:13 +0100
Subject: [PATCH] afs: use random UUID

AFS uses a time based UUID to identify the host itself. This requires
getting a timestamp which is currently done through the getnstimeofday()
interface that we want to eventually get rid of.

Instead of replacing it with a ktime based interface, this simply
removes the entire function and uses generate_random_uuid() instead,
which has a v4 ("completely random") uuid instead of the time based one.

Signed-off-by: Arnd Bergmann <arnd@...db.de>

diff --git a/fs/afs/main.c b/fs/afs/main.c
index f8188feb03ad..9944770849da 100644
--- a/fs/afs/main.c
+++ b/fs/afs/main.c
@@ -35,49 +35,6 @@ struct afs_uuid afs_uuid;
 struct workqueue_struct *afs_wq;
 
 /*
- * get a client UUID
- */
-static int __init afs_get_client_UUID(void)
-{
-	struct timespec ts;
-	u64 uuidtime;
-	u16 clockseq;
-	int ret;
-
-	/* read the MAC address of one of the external interfaces and construct
-	 * a UUID from it */
-	ret = afs_get_MAC_address(afs_uuid.node, sizeof(afs_uuid.node));
-	if (ret < 0)
-		return ret;
-
-	getnstimeofday(&ts);
-	uuidtime = (u64) ts.tv_sec * 1000 * 1000 * 10;
-	uuidtime += ts.tv_nsec / 100;
-	uuidtime += AFS_UUID_TO_UNIX_TIME;
-	afs_uuid.time_low = uuidtime;
-	afs_uuid.time_mid = uuidtime >> 32;
-	afs_uuid.time_hi_and_version = (uuidtime >> 48) & AFS_UUID_TIMEHI_MASK;
-	afs_uuid.time_hi_and_version |= AFS_UUID_VERSION_TIME;
-
-	get_random_bytes(&clockseq, 2);
-	afs_uuid.clock_seq_low = clockseq;
-	afs_uuid.clock_seq_hi_and_reserved =
-		(clockseq >> 8) & AFS_UUID_CLOCKHI_MASK;
-	afs_uuid.clock_seq_hi_and_reserved |= AFS_UUID_VARIANT_STD;
-
-	_debug("AFS UUID: %08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x",
-	       afs_uuid.time_low,
-	       afs_uuid.time_mid,
-	       afs_uuid.time_hi_and_version,
-	       afs_uuid.clock_seq_hi_and_reserved,
-	       afs_uuid.clock_seq_low,
-	       afs_uuid.node[0], afs_uuid.node[1], afs_uuid.node[2],
-	       afs_uuid.node[3], afs_uuid.node[4], afs_uuid.node[5]);
-
-	return 0;
-}
-
-/*
  * initialise the AFS client FS module
  */
 static int __init afs_init(void)
@@ -86,9 +43,7 @@ static int __init afs_init(void)
 
 	printk(KERN_INFO "kAFS: Red Hat AFS client v0.1 registering.\n");
 
-	ret = afs_get_client_UUID();
-	if (ret < 0)
-		return ret;
+	generate_random_uuid((unsigned char *)&afs_uuid);
 
 	/* create workqueue */
 	ret = -ENOMEM;