On Thursday 24 June 2004 2:01 am, jiht@xxxxxxxxx wrote: > Hello, > > I want to block IO coming from filesystem while mapping bh. If the MD is > read and written as a file (like dd if=/dev/zero of=/dev/mapper/vd0 > ...), we can override the ops->read() and ops->write() of the MD > (/dev/mapper/vd0), and block the reading and writing properly. But if we > make a filesystem on the MD and read/write through the filesystem I do > not know how to achieve this. > > There is a function named __lock_fs() in dm.c in kernel-2.6.6, which calls > the function of freeze_bdev() in buffer.c. I have two questions about > these functions: > > 1. If __lock_fs() can block all current reading and writing coming from the > filesystem based on the MD which we controlled? > > 2. If there is any similar function can be called by MD in kernel-2.4.*? > How can we block all current reading and writing coming from the filesystem > based on the MD? As I know, dm_suspend() in dm.c can defer the IO, but can > not block it. What exactly are you trying to accomplish by "blocking" I/O? If you're talking about this from the Device-Mapper perspective, we don't care whether the I/O comes from a filesystem or if someone is reading/writing directly to the device. If you want to temporarily suspend I/O, you can simply suspend the DM device. When you resume the device, all the pending I/O will be submitted. But you seem to indicate you want to permanently suspend I/O, which is a horrible idea. All that does is eat up system resources that will never be returned, not to mention that the submitter of the I/Os will have no idea that their I/Os will never complete. If you just want to prevent any more I/O from reaching the physical disks, you can reload the DM device with an "error" or "zero" mapping, which will immediately return all I/O requests, either with an error indicator or a zero-filled buffer. Please give us some more details about what your ultimate goal is, and we can try to suggest the proper way to accomplish it using DM. -- Kevin Corry kevcorry@xxxxxxxxxx http://evms.sourceforge.net/
