Re: md-cluster Module Requirement

[NeilBrown <nfbrown@novell.com>]

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On Thu, Sep 01 2016, Guoqing Jiang wrote:

> On 08/26/2016 10:40 AM, Marc Smith wrote:
>> Hi,
>>
>> I'm attempting to use md-cluster from Linux 4.5.2 with mdadm 3.4 and
>> I'm running into this when attempting to create a RAID1 device with
>> the clustered bitmap:
>>
>> --snip--
>> [64782.619968] md: bind<dm-4>
>> [64782.629336] md: bind<dm-3>
>> [64782.630008] md/raid1:md127: active with 2 out of 2 mirrors
>> [64782.630528] md-cluster module not found.
>> [64782.630530] md127: Could not setup cluster service (-2)
>> [64782.630531] md127: bitmap file superblock:
>> [64782.630532]          magic: 6d746962
>> [64782.630533]        version: 5
>> [64782.630534]           uuid: 10fee18f.f553d7f2.deb926f1.c7c4bd4b
>> [64782.630534]         events: 0
>> [64782.630535] events cleared: 0
>> [64782.630536]          state: 00000000
>> [64782.630537]      chunksize: 67108864 B
>> [64782.630537]   daemon sleep: 5s
>> [64782.630538]      sync size: 878956288 KB
>> [64782.630539] max write behind: 0
>> [64782.630541] md127: failed to create bitmap (-2)
>> [64782.630577] md: md127 stopped.
>> [64782.630581] md: unbind<dm-3>
>> [64782.635133] md: export_rdev(dm-3)
>> [64782.635145] md: unbind<dm-4>
>> [64782.643111] md: export_rdev(dm-4)
>> --snip--
>>
>> I'm using md-cluster built-in, not as a module:
>> # zcat /proc/config.gz | grep MD_CLUSTER
>> CONFIG_MD_CLUSTER=y
>>
>> It seems the driver is attempting to load the 'md-cluster' module
>> (from drivers/md/md.c):
>> --snip--
>>          err = request_module("md-cluster");
>>          if (err) {
>>                  pr_err("md-cluster module not found.\n");
>>                  return -ENOENT;
>>          }
>> --snip--

I think this code is wrong.  It should be more like:

diff --git a/drivers/md/md.c b/drivers/md/md.c
index d646f6e444f0..09036add7f33 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7612,15 +7612,13 @@ int md_setup_cluster(struct mddev *mddev, int nodes)
 {
 	int err;
 
-	err = request_module("md-cluster");
-	if (err) {
-		pr_err("md-cluster module not found.\n");
-		return -ENOENT;
-	}
+	if (!md_cluster_ops)
+		request_module("md-cluster");
 
 	spin_lock(&pers_lock);
 	if (!md_cluster_ops || !try_module_get(md_cluster_mod)) {
 		spin_unlock(&pers_lock);
+		pr_err("md-cluster module not found.\n");
 		return -ENOENT;
 	}
 	spin_unlock(&pers_lock);

>>
>> I looked at linux-next and it appears this code is the same; is there
>> a test we can do before attempting to load the module in the case that
>> its built-in, or is there some other requirement that md-cluster needs
>> to be built as a module?
>
> Yes, we need some additional modules corosync/pacemaker and dlm,

That doesn't explain the error message though.
If MD_CLUSTER is built in, then DLM must be too.

NeilBrown


> pls refer to http://www.spinics.net/lists/raid/msg47863.html, HTH.
>
> Regards,
> Guoqing
>
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