On Wednesday, 8 November 2006 16:25, Alasdair G Kergon wrote: > 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. I think the last point is handled correctly by freezing the filesystems in the reverse order - unless the fs below the loop has been frozen before by someone else, but I guess that would lead to problems anyway. > 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.) The suspended dm device in the stack is not, however. Is there any list of all dm devices in the system? Rafael -- You never change things by fighting the existing reality. R. Buckminster Fuller -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
