Re: [PATCH] common/rc: Modify _require_batched_discard to improve test coverage

[Ojaswin Mujoo]

On Fri, Apr 01, 2022 at 03:24:36PM +0530, Ritesh Harjani wrote:
> On 22/04/01 11:27AM, Ojaswin Mujoo wrote:
> > A recent ext4 patch discussed [1] that some devices (eg LVMs) can
> > have a discard granularity as big as 42MB which makes it larger
> > than the group size of ext4 FS with 1k BS. This causes the FITRIM
> > IOCTL to fail on filesystems like ext4.
> >
> > This case was not correctly handle by "_require_batched_discard" as
> > it incorrectly interpreted the FITRIM failure as fs not supporting
> > the IOCTL. This caused the tests like generic/260 to incorectly
> > report "not run" instead of "failed" in case of large discard
> > granularity.
> 
> Ok, I looked at fstrim code and it does print [1]
> "the discard operation is not supported" in case of rc == 1.
> And if rc != 0 it will always returns EXIT_FAILURE.
> 
> So this patch looks good to me. Feel free to add:
> 
> Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>

Thank you for the review Ritesh.
> 
> 
> Although it will be good to check if we can add a generic test case
> using maybe lvm or dm device, where this device could report large
> discard_granularity for actually excercising this code path
> (rather then changing kernel code to test it).
You are correct, as I was not able to simulate a device with disc gran
of 40MB+ I tested this by hard coding the granularity in the kernel. 

That being said, I would appreciate if anyone has any insights on using 
LVM/DM to get that high a granularity so I can test it more accurately.

Regards,
Ojaswin
> 
> -ritesh
> 
> [1]: https://github.com/util-linux/util-linux/blob/master/sys-utils/fstrim.c
> 
> >
> > Fix "_require_batched_discard" to use a more accurate method
> > to determine if discard is supported.
> >
> > [1] commit 173b6e383d2
> >     ext4: avoid trim error on fs with small groups
> >
> > Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> > ---
> >  common/rc | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >