Errno::ENOENT: No such file or directory @ rb_sysopen - /sys/block/sda1/queue/discard_granularity

[simonxuhao]

A lot of tests fail due to Errno::ENOENT: No such file or directory @ rb_sysopen - /sys/block/<dev>/queue/discard_granularity when dev is a partition instead of a disk, so we should first find the disk of the partition and then read the discard_granularity file of the disk.

Example failure (DiscardQuickTests_discard_past_the_end_fails.log):

E, [2020-09-02T22:17:33.415373 #38027] ERROR -- : Error:
test_discard_past_the_end_fails(DiscardQuickTests):
Errno::ENOENT: No such file or directory @ rb_sysopen - /sys/block/sda1/queue/discard_granularity
/root/device-mapper-test-suite/lib/dmtest/discard_limits.rb:17:in initialize' /root/device-mapper-test-suite/lib/dmtest/discard_limits.rb:17:in open'
/root/device-mapper-test-suite/lib/dmtest/discard_limits.rb:17:in read_param' /root/device-mapper-test-suite/lib/dmtest/discard_limits.rb:8:in initialize'
/root/device-mapper-test-suite/lib/dmtest/thinp-mixin.rb:154:in new' /root/device-mapper-test-suite/lib/dmtest/thinp-mixin.rb:154:in with_discardable_dev'
/root/device-mapper-test-suite/lib/dmtest/thinp-mixin.rb:167:in with_discardable_pool' /root/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:558:in block in class:DiscardQuickTests'
I, [2020-09-02T22:17:33.415451 #38027] INFO -- : Peak bufio allocation was 0