Do not convert blkio weight value using blkio->io conversion scheme

bfq weight controller (i.e. io.bfq.weight if present) is still using the
same bfq weight scheme (i.e 1->1000, see [1].) Unfortunately the
documentation for this was wrong, and only fixed recently [2].

Therefore, if we map blkio weight to io.bfq.weight, there's no need to
do any conversion. Otherwise, we will try to write invalid value which
results in error such as:

```
time="2021-02-03T14:55:30Z" level=error msg="container_linux.go:367: starting container process caused: process_linux.go:495: container init caused: process_linux.go:458: setting cgroup config for procHooks process caused: failed to write \"7475\": write /sys/fs/cgroup/runc-cgroups-integration-test/test-cgroup/io.bfq.weight: numerical result out of range"
```

[1] https://github.com/torvalds/linux/blob/master/Documentation/block/bfq-iosched.rst
[2] torvalds/linux@65752ae

Signed-off-by: Daniel Dao <dqminh89@gmail.com>

libcontainer/cgroups/fs2/io.go

@@ -29,7 +29,7 @@ func setIo(dirPath string, cgroup *configs.Cgroup) error {
 	if cgroup.Resources.BlkioWeight != 0 {
 		filename := "io.bfq.weight"
 		if err := fscommon.WriteFile(dirPath, filename,
-			strconv.FormatUint(cgroups.ConvertBlkIOToCgroupV2Value(cgroup.Resources.BlkioWeight), 10)); err != nil {
+			strconv.FormatUint(uint64(cgroup.Resources.BlkioWeight), 10)); err != nil {
 			return err
 		}
 	}

libcontainer/cgroups/utils.go

@@ -400,17 +400,6 @@ func WriteCgroupProc(dir string, pid int) error {
 	return err
 }
 
-// Since the OCI spec is designed for cgroup v1, in some cases
-// there is need to convert from the cgroup v1 configuration to cgroup v2
-// the formula for BlkIOWeight is y = (1 + (x - 10) * 9999 / 990)
-// convert linearly from [10-1000] to [1-10000]
-func ConvertBlkIOToCgroupV2Value(blkIoWeight uint16) uint64 {
-	if blkIoWeight == 0 {
-		return 0
-	}
-	return uint64(1 + (uint64(blkIoWeight)-10)*9999/990)
-}
-
 // Since the OCI spec is designed for cgroup v1, in some cases
 // there is need to convert from the cgroup v1 configuration to cgroup v2
 // the formula for cpuShares is y = (1 + ((x - 2) * 9999) / 262142)

libcontainer/cgroups/utils_test.go

@@ -548,20 +548,6 @@ func TestGetHugePageSizeImpl(t *testing.T) {
 	}
 }
 
-func TestConvertBlkIOToCgroupV2Value(t *testing.T) {
-	cases := map[uint16]uint64{
-		0:    0,
-		10:   1,
-		1000: 10000,
-	}
-	for i, expected := range cases {
-		got := ConvertBlkIOToCgroupV2Value(i)
-		if got != expected {
-			t.Errorf("expected ConvertBlkIOToCgroupV2Value(%d) to be %d, got %d", i, expected, got)
-		}
-	}
-}
-
 func TestConvertCPUSharesToCgroupV2Value(t *testing.T) {
 	cases := map[uint64]uint64{
 		0:      0,

tests/integration/cgroups.bats

@@ -190,6 +190,20 @@ function setup() {
 	[[ "$output" == *'invalid configuration'* ]]
 }
 
+@test "runc run (blkio weight)" {
+	requires root cgroups_v2
+
+	set_cgroups_path "$BUSYBOX_BUNDLE"
+	update_config '.linux.resources.blockIO |= {"weight": 750}' "${BUSYBOX_BUNDLE}"
+
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_cgroups_unified
+	[ "$status" -eq 0 ]
+
+	runc exec test_cgroups_unified sh -c 'cat /sys/fs/cgroup/io.bfq.weight'
+	[ "$status" -eq 0 ]
+	[ "$output" = 'default 750' ]
+}
+
 @test "runc run (cgroup v2 resources.unified only)" {
 	requires root cgroups_v2