Re: scsi_debug in fstests and blktests (Was: Re: Fwd: [bug report][bisected] modprob -r scsi-debug take more than 3mins during blktests srp/ tests)

["Theodore Ts'o" <tytso@mit.edu>]

On Thu, Apr 21, 2022 at 10:56:57PM -0700, Christoph Hellwig wrote:
> > This should also apply to other test debug modules like null_blk,
> > nvme target loop drivers, etc, it's all the same long term. But yeah
> > scsi surely make this... painful today. In any case hopefully folks
> > with other test debug drivesr are running tests to ensure you can
> > always rmmod these modules regardless of what is happening.
> 
> Maybe fix blktests to not rely on module removal  I have such a hard
> time actually using blktests because it is suck a f^^Y% broken piece
> of crap that assumes everything is modular.  Stop making that whole
> assumption and work fine with built-in driver as a first step.  Then
> start worrying about module removal.

I would love it if blktests didn't require modules, period.  That's
because it's super-convenient to be able to pluck a kernel out from
the build tree without having to install it first.  If all of the
necessary devices could be built-into the kernel, this would allow
this to work:

     make
     kvm-xfstests --blktests

which ends up running something like this:

/usr/bin/kvm -boot order=c -net none -machine type=pc,accel=kvm:tcg \
	     ... \
	     --kernel /build/ext4/arch/x86/boot/bzImage
	     --append "quiet loglevel=0 root=/dev/vda console=ttyS0,115200 nokaslr fstestopt=blktests,aex ..."

Unfortunately, because blktests requires modules, I can only do this
sort of thing using gce-xfstests and by passing in a kernel.deb file
so I can get the !@#@! modules installed.  (If I could use kexec with
gce-xfstets, I'd shave almost a minute of test appliance setup time,
and starting a GCE VM talks a minute or two extra over using
kvm-xfstests.)

I think we would need to make some changes to how scsi_debug and other
block device modules, first, though.  blktests is using modules
because that appears to be the only way to configure some of these
test/debug drivers and then have the debug device show up with the
specified characteristics.

						- Ted