Attachment 46014 Details for Bug 104046

[patch] evm patch.

bd-claim.patch (text/plain), 4.96 KB, created by enno oosterhuis on 2005-08-15 07:00:47 UTC

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Creator: enno oosterhuis

Created: 2005-08-15 07:00:47 UTC

Size: 4.96 KB

patch

obsolete

>bd-claim
>
>A patch was merged between 2.6.0-test3 and -test4 that breaks EVMS on many
>systems by not allowing Device-Mapper to activate DM devices on top of disks
>that also contain mounted partitions.
>
>More specifically, the kernel has its own partitioning code that runs when the
>kernel boots, and provides the traditional partition devices (e.g. /dev/hda1).
>When a filesystem mounts one of these partitions, the filesystem "claims" that
>partition and no one else can claim it. When this happens, the kernel's
>partitioning code (not the filesystem code) also claims the underlying disk,
>meaning that disk is only available for use by the kernel's built-in
>partitions on that disk. Other filesystems may mount other partitions on that
>disk, but the disk itself is "owned" by the partitioning code.
>
>However, in order to allow easy management of partitions, EVMS does its own
>partition detection, and creates devices to represent those partitions using
>Device-Mapper (not the kernel's built-in partitioning code). When DM creates a
>device, it also attempts to claim the underlying devices (in this case the
>disk that holds the partition). But, if the user has already mounted one of
>the kernel's built-in partitions on that same disk, then the disk will already
>have been claimed. DM will be unable to claim it, and the DM device activation
>will fail.
>
>The end result is that a single disk cannot be used both for EVMS and for
>mounting the kernel's built-in partitions. 
>
>There are three solutions to this problem.
>
>1. Switch to using EVMS for *all* your volumes and partitions. If none of the
>   kernel's built-in partitions are mounted, then there won't be any conflicts
>   when DM tries to claim the disks. This is, of course, the preferred
>   solution, but also requires some extra work on your part to convert to
>   mounting your root filesystem using an EVMS volume. Please see
>   http://evms.sf.net/install/root.html and http://evms.sf.net/convert.html
>   for more details on this option.
>
>2. Tell EVMS to exclude any disks that contain partitions that you are going
>   to mount using the kernel's built-in partitions. You can do this by adding
>   the names of these disks to the "sysfs_devices.exclude" line in your
>   /etc/evms.conf file. If you choose this option, EVMS will completely ignore
>   the specified disks and not discover any of the partitions or volumes on
>   those disks.
>
>3. Apply this patch, which will is a reversal of the patch that prevents
>   Device-Mapper and the kernel's built-in partitions from using the same disk
>   at the same time. This patch is not supported by the kernel community, and
>   in fact removes functionality that they specifically added. However, it
>   will allow you to share your disks between EVMS and the kernel's built-in
>   partitioning code, if that's the choice you wish to make for your system.
>
>   cd /usr/src/linux-2.6.10/
>   patch -p1 < bd_claim.patch
>
>
>==============================================================================
>Current devices can be 'claimed' by filesystems (when mounting) or
>md/raid (when being included in an array) or 'raw' or ....
>This stop concurrent access by these systems.
>
>However it is still possible for one system to claim the whole device
>and a second system to claim one partition, which is not good.
>
>With this patch, when a partition is claimed, the whole device is
>claimed for partitioning.  So you cannot have a partition and the
>whole devices claimed at the same time (except if the whole device
>is claimed for partitioning).
>
>--- diff/fs/block_dev.c	2005-02-28 08:36:45.603361144 -0600
>+++ source/fs/block_dev.c	2005-02-28 09:30:13.347709880 -0600
>@@ -445,34 +445,12 @@
> 
> int bd_claim(struct block_device *bdev, void *holder)
> {
>-	int res;
>+	int res = -EBUSY;
> 	spin_lock(&bdev_lock);
>-
>-	/* first decide result */
>-	if (bdev->bd_holder == holder)
>-		res = 0;	 /* already a holder */
>-	else if (bdev->bd_holder != NULL)
>-		res = -EBUSY; 	 /* held by someone else */
>-	else if (bdev->bd_contains == bdev)
>-		res = 0;  	 /* is a whole device which isn't held */
>-
>-	else if (bdev->bd_contains->bd_holder == bd_claim)
>-		res = 0; 	 /* is a partition of a device that is being partitioned */
>-	else if (bdev->bd_contains->bd_holder != NULL)
>-		res = -EBUSY;	 /* is a partition of a held device */
>-	else
>-		res = 0;	 /* is a partition of an un-held device */
>-
>-	/* now impose change */
>-	if (res==0) {
>-		/* note that for a whole device bd_holders
>-		 * will be incremented twice, and bd_holder will
>-		 * be set to bd_claim before being set to holder
>-		 */
>-		bdev->bd_contains->bd_holders ++;
>-		bdev->bd_contains->bd_holder = bd_claim;
>-		bdev->bd_holders++;
>+	if (!bdev->bd_holder || bdev->bd_holder == holder) {
> 		bdev->bd_holder = holder;
>+		bdev->bd_holders++;
>+		res = 0;
> 	}
> 	spin_unlock(&bdev_lock);
> 	return res;
>@@ -483,8 +461,6 @@
> void bd_release(struct block_device *bdev)
> {
> 	spin_lock(&bdev_lock);
>-	if (!--bdev->bd_contains->bd_holders)
>-		bdev->bd_contains->bd_holder = NULL;
> 	if (!--bdev->bd_holders)
> 		bdev->bd_holder = NULL;
> 	spin_unlock(&bdev_lock);

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Attachments on bug 104046: 46014