On Thu, Dec 02 2010 at 9:17am -0500, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Thu, Dec 02, 2010 at 03:14:28PM +0100, Spelic wrote: > > On 12/02/2010 03:11 PM, Christoph Hellwig wrote: > > >I'm pretty sure you have CONFIG_DEBUG_BLOCK_EXT_DEVT enabled. This > > >option must never be enabled, as it causes block devices to be > > >randomly renumered. Together with the ramdisk driver overloading > > >the BLKFLSBUF ioctl to discard all data it guarantees you to get > > >data loss like yours. > > > > Nope... > > > > # CONFIG_DEBUG_BLOCK_EXT_DEVT is not set > > Hmm, I suspect dm-linear's dumb forwarding of ioctls has the same > effect. For the benefit of others: - mkfs.xfs will avoid sending BLKFLSBUF to any device whose major is ramdisk's major, this dates back to 2004: http://oss.sgi.com/archives/xfs/2004-08/msg00463.html - but because a kpartx partition overlay (linear DM mapping) is used for the /dev/ram0p1 device, mkfs.xfs only sees a device with DM's major - so mkfs.xfs sends BLKFLSBUF to the DM device blissfully unaware that the backing device (behind the DM linear target) is a brd device - DM will forward the BLKFLSBUF ioctl to brd, which triggers drivers/block/brd.c:brd_ioctl (nuking the entire ramdisk in the process) So coming full circle this is what hch was referring to when he mentioned: 1) "ramdisk driver overloading the BLKFLSBUF ioctl ..." 2) "dm-linear's dumb forwarding of ioctls ..." I really can't see DM adding a specific check for ramdisk's major when forwarding the BLKFLSBUF ioctl. brd has direct partition support (see commit d7853d1f8932c) so maybe kpartx should just blacklist /dev/ram devices? Alternatively, what about switching brd away from overloading BLKFLSBUF to a real implementation of (overloaded) BLKDISCARD support in brd.c? One that doesn't blindly nuke the entire device but that properly processes the discard request. Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
