On Fri, Mar 14 2014 at 9:23am -0400, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Fri, Mar 14, 2014 at 09:00:21AM -0400, Mike Snitzer wrote: > > > Getting a little upset, eh? I didn't say it's broken, I said it gets > > > very little testing. The regression from me was found like so many > > > before only after it was backported o some enterprise kernel. > > > > Even _really_ basic dm-multipath testing would've uncovered this bug. > > But major testing using dm, md and various low-level drivers didn't. Do > you really expect everyone to remember to specificly test dm-multipath > for a core block change? Without a nicely documented way to do it? > > That being said I should have remembered that it's special, but even I > didn't and I'm sorry about that. I was more reacting to the assertion you made like multipath regresses all the time. I'm not faulting you at all for not having tested multipath. Hell, I even forget to test multipath more than I should. /me says with shame I'll work to add basic coverage for dm-multipath to the device-mapper-test-suite. > > > I think the problem here is two-fold: > > > a) the hardware you use with dm-multipath isn't widely available. > > > b) it uses a very special code path in the block layer no one else uses > > > > > > a) might be fixable by having some RDAC or similar emulation in qemu if > > > someone wants to spend the effort. > > > > The regression from the commit in question was easily reproduced/tested > > using scsi_debug. Just start the multipathd service and any scsi_debug > > device in the system will get multipath'd. > > Really? That sounds a like a bug in the INQUIRY information returned by > scsi_debug. Either way please write up these things in Documentation so > you can point people at it easily. Yeah, not sure why single path scsi_debug "just works", maybe it is a "feature" of the older multipathd I have kicking around?, but for basic data path testing scsi_debug is a quick means to an end. I can look closer at _why_ it gets multipathd in a bit. But maybe Ben or Hannes will have quicker insight? For me, if multipathd is running, if I issue the following a multipath device gets layered ontop of the associated scsi_debug created sd device: modprobe scsi_debug dev_size_mb=1024 I think it useful to have scsi_debug work with multipath. I know people in Red Hat's QE organization have even simulated multiple paths with it.. but I don't recall if they had to hack scsi_debug to do that. I'll try to find out. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
