[Patch] kpartx to accept device map name

[Patch] kpartx to accept device map name

[Jun'ichi Nomura]

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Hello Christophe,

Attached patch adds '-m' option which makes kpartx
to accept device map name.

Using with the cvs version of libdevmapper or with the
patch suggested by Kiyoshi Ueda today, we don't need
to depend on asynchronous nature of hotplug when it's
not necessary.

For example, we can do this for initialization:
  multipath
  dmsetup info -c --noheadings -o name | xargs -l1 kpartx -a -m
otherwise we had to insert adhoc length of sleep to wait for
the completion of hotplug events.

Please consider to apply.

Thanks,
Jun'ichi Nomura


[-- Attachment #2: kpartx-mapname.patch --]
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Index: kpartx/kpartx.c
===================================================================
--- e5bb12309df918f41b63a339fdc936f77241d332/kpartx/kpartx.c  (mode:100644)
+++ uncommitted/kpartx/kpartx.c  (mode:100644)
@@ -70,7 +70,7 @@
 	addpts("unixware", read_unixware_pt);
 }
 
-static char short_opts[] = "ladgvnp:t:";
+static char short_opts[] = "ladgvnp:t:m";
 
 /* Used in gpt.c */
 int force_gpt=0;
@@ -183,6 +183,7 @@
 	char * delim = NULL;
 	int loopro = 0;
 	int hotplug = 0;
+	int use_mapname = 0;
 	struct stat buf;
 
 	initpts();
@@ -245,12 +246,16 @@
 		case 'd':
 			what = DELETE;
 			break;
+		case 'm':
+			use_mapname = 1;
+			break;
 		default:
 			usage();
 			exit(1);
 	}
 
-	if (dm_prereq(DM_TARGET, 0, 0, 0) && (what == ADD || what == DELETE)) {
+	if (dm_prereq(DM_TARGET, 0, 0, 0)
+	    && (what == ADD || what == DELETE || use_mapname)) {
 		fprintf(stderr, "device mapper prerequisites not met\n"); 
 		exit(1);
 	}
@@ -267,6 +272,21 @@
 		exit(1);
 	}
 
+	if (use_mapname) {
+		int len;
+		char *realdev, *dmdir;
+
+		dmdir = dm_dir();
+		len = strlen(dmdir) + strlen(device) + 2;
+		realdev = malloc(sizeof(char) * len);
+		if (!realdev) {
+			printf("failed to alloc memory\n");
+			exit(1);
+		}
+		snprintf(realdev, len, "%s/%s", dmdir, device);
+		diskdevice = device = realdev;
+	}
+
 	if (stat(device, &buf)) {
 		printf("failed to stat() %s\n", device);
 		exit (1);

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Re: [Patch] kpartx to accept device map name

[christophe varoqui]

I applied Kiyoshi"s patch.

Can you elaborate on the problems you see with the asynchronous hotplug
model ?

I would like to express my reluctance to add a devmap special case to
kpartx.

Regards,
cvaroqui

On lun, 2005-05-16 at 15:21 -0400, Jun'ichi Nomura wrote:
> Hello Christophe,
> 
> Attached patch adds '-m' option which makes kpartx
> to accept device map name.
> 
> Using with the cvs version of libdevmapper or with the
> patch suggested by Kiyoshi Ueda today, we don't need
> to depend on asynchronous nature of hotplug when it's
> not necessary.
> 
> For example, we can do this for initialization:
>   multipath
>   dmsetup info -c --noheadings -o name | xargs -l1 kpartx -a -m
> otherwise we had to insert adhoc length of sleep to wait for
> the completion of hotplug events.
> 
> Please consider to apply.
> 
> Thanks,
> Jun'ichi Nomura
> 
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
-- 
christophe varoqui <christophe.varoqui@free.fr>

Re: [Patch] kpartx to accept device map name

[Jun'ichi Nomura]

Hi,

Excuse me for the misleading message.

The problem I saw was that when executing kpartx just after
multipath (in shell script), kpartx was invoked too early
and couldn't see the device node. I could avoid it by
inserting "sleep 5" after multipath execution but I can't
tell whether it's enough.
Kiyoshi's patch should fix it and the device node will be
created on the location which libdevmapper knows. (/dev/mapper)

'-m' option provides a way to avoid dependency to hidden knowledge
about the location (/dev or /dev/mapper or anywhere else).
Without this, we have to synchronize udev rules, hotplug shell
scripts and initscripts to see the same device node for dm devices.
This is why I thought it's better to give kpartx an option like this.

..However, in the really latest CVS, dmsetup has a new function
to execute external command with device node name.
So we can do the same thing with dmsetup now.
Given that you are reluctant to add kpartx more relationship with
libdevmapper, dmsetup is the best place.

Thanks,
Jun'ichi Nomura

christophe varoqui wrote:
> Can you elaborate on the problems you see with the asynchronous hotplug
> model ?
> 
> I would like to express my reluctance to add a devmap special case to
> kpartx.
> 
> On lun, 2005-05-16 at 15:21 -0400, Jun'ichi Nomura wrote:
>>Attached patch adds '-m' option which makes kpartx
>>to accept device map name.