Messages in this thread | | | Date | Wed, 8 Nov 2006 15:25:33 +0000 | From | Alasdair G Kergon <> | Subject | Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex |
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On Wed, Nov 08, 2006 at 03:43:26PM +0100, Rafael J. Wysocki wrote: > Will it be enough to cover the interactions with dm?
There are cases where you *cannot* freeze the filesystem (unless you wait for userspace processes to finish what they are doing) - and only dm can tell you that.
The freeze_filesystems() code ought to do it's best in any given circumstances within the constraints.
So: Get the filesystem's block device. Check the full tree of devices that that block device depends upon and for any device that belongs to device-mapper check if it is suspended. If it is, skip the original device.
struct mapped_device *dm_get_md(dev_t dev); int dm_suspended(struct mapped_device *md); void dm_put(struct mapped_device *md);
Handling the tree is the difficult bit, but sysfs could help. [You can get the device-mapper dependencies with: struct mapped_device *dm_get_md(dev_t dev); struct dm_table *dm_get_table(struct mapped_device *md); struct list_head *dm_table_get_devices(struct dm_table *t); void dm_table_put(struct dm_table *t); void dm_put(struct mapped_device *md); ]
Consider that you could have an already-frozen filesystem containing a loop device containing a device-mapper device containing a not-frozen filesystem. You won't be able to freeze that top filesystem because the I/O would queue lower down the stack. (Similar problem if the device-mapper device in the stack was suspended.)
Alasdair -- agk@redhat.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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