libct/cg/sd/v2: support cpuset.* / Allowed*

* cpuset.cpus -> AllowedCPUs
 * cpuset.mems -> AllowedMemoryNodes

No test for cgroup v2 resources.unified override, as this requires a
separate test case, and all the unified resources are handled uniformly
so there's little sense to test all parameters.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

go.mod

@@ -22,5 +22,6 @@ require (
 	// NOTE: urfave/cli must be <= v1.22.1 due to a regression: https://github.com/urfave/cli/issues/1092
 	github.com/urfave/cli v1.22.1
 	github.com/vishvananda/netlink v1.1.0
+	github.com/willf/bitset v1.1.11
 	golang.org/x/sys v0.0.0-20200916030750-2334cc1a136f
 )

go.sum

@@ -62,6 +62,8 @@ github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df h1:OviZH7qLw/7Zo
 github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df/go.mod h1:JP3t17pCcGlemwknint6hfoeCVQrEMVwxRLRjXpq+BU=
 github.com/willf/bitset v1.1.11-0.20200630133818-d5bec3311243 h1:R43TdZy32XXSXjJn7M/HhALJ9imq6ztLnChfYJpVDnM=
 github.com/willf/bitset v1.1.11-0.20200630133818-d5bec3311243/go.mod h1:RjeCKbqT1RxIR/KWY6phxZiaY1IyutSBfGjNPySAYV4=
+github.com/willf/bitset v1.1.11 h1:N7Z7E9UvjW+sGsEl7k/SJrvY2reP1A07MrGuCjIOjRE=
+github.com/willf/bitset v1.1.11/go.mod h1:83CECat5yLh5zVOf4P1ErAgKA5UDvKtgyUABdr3+MjI=
 golang.org/x/sys v0.0.0-20190606203320-7fc4e5ec1444/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191115151921-52ab43148777/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

libcontainer/cgroups/systemd/cpuset.go

@@ -0,0 +1,67 @@
+package systemd
+
+import (
+	"encoding/binary"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+	"github.com/willf/bitset"
+)
+
+// rangeToBits converts a text representation of a CPU mask (as written to
+// or read from cgroups' cpuset.* files, e.g. "1,3-5") to a slice of bytes
+// with the corresponding bits set (as consumed by systemd over dbus as
+// AllowedCPUs/AllowedMemoryNodes unit property value).
+func rangeToBits(str string) ([]byte, error) {
+	bits := &bitset.BitSet{}
+
+	for _, r := range strings.Split(str, ",") {
+		// allow extra spaces around
+		r = strings.TrimSpace(r)
+		// allow empty elements (extra commas)
+		if r == "" {
+			continue
+		}
+		ranges := strings.SplitN(r, "-", 2)
+		if len(ranges) > 1 {
+			start, err := strconv.ParseUint(ranges[0], 10, 32)
+			if err != nil {
+				return nil, err
+			}
+			end, err := strconv.ParseUint(ranges[1], 10, 32)
+			if err != nil {
+				return nil, err
+			}
+			if start > end {
+				return nil, errors.New("invalid range: " + r)
+			}
+			for i := uint(start); i <= uint(end); i++ {
+				bits.Set(i)
+			}
+		} else {
+			val, err := strconv.ParseUint(ranges[0], 10, 32)
+			if err != nil {
+				return nil, err
+			}
+			bits.Set(uint(val))
+		}
+	}
+
+	val := bits.Bytes()
+	if len(val) == 0 {
+		// do not allow empty values
+		return nil, errors.New("empty value")
+	}
+	ret := make([]byte, len(val)*8)
+	for i := range val {
+		// bitset uses BigEndian internally
+		binary.BigEndian.PutUint64(ret[i*8:], val[len(val)-1-i])
+	}
+	// remove upper all-zero bytes
+	for ret[0] == 0 {
+		ret = ret[1:]
+	}
+
+	return ret, nil
+}

libcontainer/cgroups/systemd/cpuset_test.go

@@ -0,0 +1,58 @@
+package systemd
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestRangeToBits(t *testing.T) {
+	testCases := []struct {
+		in    string
+		out   []byte
+		isErr bool
+	}{
+		{in: "", isErr: true},
+		{in: "0", out: []byte{1}},
+		{in: "1", out: []byte{2}},
+		{in: "0-1", out: []byte{3}},
+		{in: "0,1", out: []byte{3}},
+		{in: ",0,1,", out: []byte{3}},
+		{in: "0-3", out: []byte{0x0f}},
+		{in: "0,1,2-3", out: []byte{0x0f}},
+		{in: "4-7", out: []byte{0xf0}},
+		{in: "0-7", out: []byte{0xff}},
+		{in: "0-15", out: []byte{0xff, 0xff}},
+		{in: "16", out: []byte{1, 0, 0}},
+		{in: "0-3,32-33", out: []byte{3, 0, 0, 0, 0x0f}},
+		// extra spaces and tabs are ok
+		{in: "1, 2, 1-2", out: []byte{6}},
+		{in: "    , 1   , 3  ,  5-7,	", out: []byte{0xea}},
+		// somewhat large values
+		{in: "128-130,1", out: []byte{7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2}},
+
+		{in: "-", isErr: true},
+		{in: "1-", isErr: true},
+		{in: "-3", isErr: true},
+		// bad range (start > end)
+		{in: "54-53", isErr: true},
+		// kernel does not allow extra spaces inside a range
+		{in: "1 - 2", isErr: true},
+	}
+
+	for _, tc := range testCases {
+		t.Logf("case: %q", tc.in)
+		out, err := rangeToBits(tc.in)
+		if err != nil {
+			t.Logf("   got error: %s", err)
+			if !tc.isErr {
+				t.Error("   ^^^ unexpected error")
+			}
+
+			continue
+		}
+		t.Logf("   expected %v, got %v", tc.out, out)
+		if !bytes.Equal(out, tc.out) {
+			t.Error("   ^^^ unexpected result")
+		}
+	}
+}

libcontainer/cgroups/systemd/v2.go

@@ -93,6 +93,18 @@ func unifiedResToSystemdProps(conn *systemdDbus.Conn, res map[string]string) (pr
 			props = append(props,
 				newProp("CPUWeight", num))
 
+		case "cpuset.cpus", "cpuset.mems":
+			bits, err := rangeToBits(v)
+			if err != nil {
+				return nil, fmt.Errorf("unified resource %q=%q conversion error: %w", k, v, err)
+			}
+			m := map[string]string{
+				"cpuset.cpus": "AllowedCPUs",
+				"cpuset.mems": "AllowedMemoryNodes",
+			}
+			props = append(props,
+				newProp(m[k], bits))
+
 		case "pids.max":
 			num := uint64(math.MaxUint64)
 			if v != "max" {

tests/integration/helpers.bash

@@ -357,6 +357,12 @@ function requires() {
 				skip_me=1
 			fi
 			;;
+		smp)
+			local cpu_count=$(grep -c '^processor' /proc/cpuinfo)
+			if [ "$cpu_count" -lt 2 ]; then
+				skip_me=1
+			fi
+			;;
 		systemd)
 			if [ -z "${RUNC_USE_SYSTEMD}" ]; then
 				skip_me=1

tests/integration/update.bats

@@ -392,6 +392,53 @@ EOF
 	check_systemd_value "TasksMax" 10
 }
 
+@test "update cpuset parameters via v2 unified map" {
+	[[ "$ROOTLESS" -ne 0 ]] && requires rootless_cgroup
+	requires cgroups_v2 smp
+
+	update_config ' .linux.resources.unified |= {
+				"cpuset.cpus": "0",
+				"cpuset.mems": "0"
+			}' "${BUSYBOX_BUNDLE}"
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_update
+	[ "$status" -eq 0 ]
+
+	# check that initial values were properly set
+	check_systemd_value "AllowedCPUs" 0
+	check_systemd_value "AllowedMemoryNodes" 0
+
+	runc update -r - test_update <<EOF
+{
+  "unified": {
+    "cpuset.cpus": "1"
+  }
+}
+EOF
+	[ "$status" -eq 0 ]
+
+	# check the updated systemd unit properties
+	check_systemd_value "AllowedCPUs" 1
+
+	# More than 1 numa memory node is required to test this
+	file="/sys/fs/cgroup/cpuset.mems.effective"
+	if ! test -r $file || grep -q '^0$' $file; then
+		# skip the rest of it
+		return 0
+	fi
+
+	runc update -r - test_update <<EOF
+{
+  "unified": {
+    "cpuset.mems": "1"
+  }
+}
+EOF
+	[ "$status" -eq 0 ]
+
+	# check the updated systemd unit properties
+	check_systemd_value "AllowedMemoryNodes" 1
+}
+
 @test "update rt period and runtime" {
 	[[ "$ROOTLESS" -ne 0 ]] && requires rootless_cgroup
 	requires cgroups_v1 cgroups_rt no_systemd

vendor/github.com/willf/bitset/Makefile

@@ -1,191 +0,0 @@
-# MAKEFILE
-#
-# @author      Nicola Asuni <info@tecnick.com>
-# @link        https://github.com/willf/bitset
-# ------------------------------------------------------------------------------
-
-# List special make targets that are not associated with files
-.PHONY: help all test format fmtcheck vet lint coverage cyclo ineffassign misspell structcheck varcheck errcheck gosimple astscan qa deps clean nuke
-
-# Use bash as shell (Note: Ubuntu now uses dash which doesn't support PIPESTATUS).
-SHELL=/bin/bash
-
-# CVS path (path to the parent dir containing the project)
-CVSPATH=github.com/willf
-
-# Project owner
-OWNER=willf
-
-# Project vendor
-VENDOR=willf
-
-# Project name
-PROJECT=bitset
-
-# Project version
-VERSION=$(shell cat VERSION)
-
-# Name of RPM or DEB package
-PKGNAME=${VENDOR}-${PROJECT}
-
-# Current directory
-CURRENTDIR=$(shell pwd)
-
-# GO lang path
-ifneq ($(GOPATH),)
-	ifeq ($(findstring $(GOPATH),$(CURRENTDIR)),)
-		# the defined GOPATH is not valid
-		GOPATH=
-	endif
-endif
-ifeq ($(GOPATH),)
-	# extract the GOPATH
-	GOPATH=$(firstword $(subst /src/, ,$(CURRENTDIR)))
-endif
-
-# --- MAKE TARGETS ---
-
-# Display general help about this command
-help:
-	@echo ""
-	@echo "$(PROJECT) Makefile."
-	@echo "GOPATH=$(GOPATH)"
-	@echo "The following commands are available:"
-	@echo ""
-	@echo "    make qa          : Run all the tests"
-	@echo "    make test        : Run the unit tests"
-	@echo ""
-	@echo "    make format      : Format the source code"
-	@echo "    make fmtcheck    : Check if the source code has been formatted"
-	@echo "    make vet         : Check for suspicious constructs"
-	@echo "    make lint        : Check for style errors"
-	@echo "    make coverage    : Generate the coverage report"
-	@echo "    make cyclo       : Generate the cyclomatic complexity report"
-	@echo "    make ineffassign : Detect ineffectual assignments"
-	@echo "    make misspell    : Detect commonly misspelled words in source files"
-	@echo "    make structcheck : Find unused struct fields"
-	@echo "    make varcheck    : Find unused global variables and constants"
-	@echo "    make errcheck    : Check that error return values are used"
-	@echo "    make gosimple    : Suggest code simplifications"
-	@echo "    make astscan     : GO AST scanner"
-	@echo ""
-	@echo "    make docs        : Generate source code documentation"
-	@echo ""
-	@echo "    make deps        : Get the dependencies"
-	@echo "    make clean       : Remove any build artifact"
-	@echo "    make nuke        : Deletes any intermediate file"
-	@echo ""
-
-# Alias for help target
-all: help
-
-# Run the unit tests
-test:
-	@mkdir -p target/test
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) \
-	go test \
-	-covermode=atomic \
-	-bench=. \
-	-race \
-	-cpuprofile=target/report/cpu.out \
-	-memprofile=target/report/mem.out \
-	-mutexprofile=target/report/mutex.out \
-	-coverprofile=target/report/coverage.out \
-	-v ./... | \
-	tee >(PATH=$(GOPATH)/bin:$(PATH) go-junit-report > target/test/report.xml); \
-	test $${PIPESTATUS[0]} -eq 0
-
-# Format the source code
-format:
-	@find . -type f -name "*.go" -exec gofmt -s -w {} \;
-
-# Check if the source code has been formatted
-fmtcheck:
-	@mkdir -p target
-	@find . -type f -name "*.go" -exec gofmt -s -d {} \; | tee target/format.diff
-	@test ! -s target/format.diff || { echo "ERROR: the source code has not been formatted - please use 'make format' or 'gofmt'"; exit 1; }
-
-# Check for syntax errors
-vet:
-	GOPATH=$(GOPATH) go vet .
-
-# Check for style errors
-lint:
-	GOPATH=$(GOPATH) PATH=$(GOPATH)/bin:$(PATH) golint .
-
-# Generate the coverage report
-coverage:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) \
-	go tool cover -html=target/report/coverage.out -o target/report/coverage.html
-
-# Report cyclomatic complexity
-cyclo:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) gocyclo -avg ./ | tee target/report/cyclo.txt ; test $${PIPESTATUS[0]} -eq 0
-
-# Detect ineffectual assignments
-ineffassign:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) ineffassign ./ | tee target/report/ineffassign.txt ; test $${PIPESTATUS[0]} -eq 0
-
-# Detect commonly misspelled words in source files
-misspell:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) misspell -error ./  | tee target/report/misspell.txt ; test $${PIPESTATUS[0]} -eq 0
-
-# Find unused struct fields
-structcheck:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) structcheck -a ./  | tee target/report/structcheck.txt
-
-# Find unused global variables and constants
-varcheck:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) varcheck -e ./  | tee target/report/varcheck.txt
-
-# Check that error return values are used
-errcheck:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) errcheck ./  | tee target/report/errcheck.txt
-
-# AST scanner
-astscan:
-	@mkdir -p target/report
-	GOPATH=$(GOPATH) gosec . | tee target/report/astscan.txt ; test $${PIPESTATUS[0]} -eq 0 || true
-
-# Generate source docs
-docs:
-	@mkdir -p target/docs
-	nohup sh -c 'GOPATH=$(GOPATH) godoc -http=127.0.0.1:6060' > target/godoc_server.log 2>&1 &
-	wget --directory-prefix=target/docs/ --execute robots=off --retry-connrefused --recursive --no-parent --adjust-extension --page-requisites --convert-links http://127.0.0.1:6060/pkg/github.com/${VENDOR}/${PROJECT}/ ; kill -9 `lsof -ti :6060`
-	@echo '<html><head><meta http-equiv="refresh" content="0;./127.0.0.1:6060/pkg/'${CVSPATH}'/'${PROJECT}'/index.html"/></head><a href="./127.0.0.1:6060/pkg/'${CVSPATH}'/'${PROJECT}'/index.html">'${PKGNAME}' Documentation ...</a></html>' > target/docs/index.html
-
-# Alias to run all quality-assurance checks
-qa: fmtcheck test vet lint coverage cyclo ineffassign misspell structcheck varcheck errcheck gosimple astscan
-
-# --- INSTALL ---
-
-# Get the dependencies
-deps:
-	GOPATH=$(GOPATH) go get ./...
-	GOPATH=$(GOPATH) go get golang.org/x/lint/golint
-	GOPATH=$(GOPATH) go get github.com/jstemmer/go-junit-report
-	GOPATH=$(GOPATH) go get github.com/axw/gocov/gocov
-	GOPATH=$(GOPATH) go get github.com/fzipp/gocyclo
-	GOPATH=$(GOPATH) go get github.com/gordonklaus/ineffassign
-	GOPATH=$(GOPATH) go get github.com/client9/misspell/cmd/misspell
-	GOPATH=$(GOPATH) go get github.com/opennota/check/cmd/structcheck
-	GOPATH=$(GOPATH) go get github.com/opennota/check/cmd/varcheck
-	GOPATH=$(GOPATH) go get github.com/kisielk/errcheck
-	GOPATH=$(GOPATH) go get github.com/securego/gosec/cmd/gosec/...
-
-# Remove any build artifact
-clean:
-	GOPATH=$(GOPATH) go clean ./...
-
-# Deletes any intermediate file
-nuke:
-	rm -rf ./target
-	GOPATH=$(GOPATH) go clean -i ./...

vendor/github.com/willf/bitset/README.md

@@ -2,10 +2,10 @@
 
 *Go language library to map between non-negative integers and boolean values*
 
-[![Master Build Status](https://secure.travis-ci.org/willf/bitset.png?branch=master)](https://travis-ci.org/willf/bitset?branch=master)
+[![Test](https://github.com/willf/bitset/workflows/Test/badge.svg)](https://github.com/willf/bitset/actions?query=workflow%3ATest)
 [![Master Coverage Status](https://coveralls.io/repos/willf/bitset/badge.svg?branch=master&service=github)](https://coveralls.io/github/willf/bitset?branch=master)
 [![Go Report Card](https://goreportcard.com/badge/github.com/willf/bitset)](https://goreportcard.com/report/github.com/willf/bitset)
-[![GoDoc](https://godoc.org/github.com/willf/bitset?status.svg)](http://godoc.org/github.com/willf/bitset)
+[![PkgGoDev](https://pkg.go.dev/badge/github.com/willf/bitset?tab=doc)](https://pkg.go.dev/github.com/willf/bitset?tab=doc)
 
 
 ## Description
@@ -63,8 +63,11 @@ func main() {
 
 As an alternative to BitSets, one should check out the 'big' package, which provides a (less set-theoretical) view of bitsets.
 
-Godoc documentation is at: https://godoc.org/github.com/willf/bitset
+Package documentation is at: https://pkg.go.dev/github.com/willf/bitset?tab=doc
 
+## Memory Usage
+
+The memory usage of a bitset using N bits is at least N/8 bytes. The number of bits in a bitset is at least as large as one plus the greatest bit index you have accessed. Thus it is possible to run out of memory while using a bitset. If you have lots of bits, you might prefer compressed bitsets, like the [Roaring bitmaps](http://roaringbitmap.org) and its [Go implementation](https://github.com/RoaringBitmap/roaring).
 
 ## Implementation Note
 
@@ -82,15 +85,10 @@ go get github.com/willf/bitset
 
 If you wish to contribute to this project, please branch and issue a pull request against master ("[GitHub Flow](https://guides.github.com/introduction/flow/)")
 
-This project include a Makefile that allows you to test and build the project with simple commands.
-To see all available options:
-```bash
-make help
-```
-
 ## Running all tests
 
-Before committing the code, please check if it passes all tests using (note: this will install some dependencies):
+Before committing the code, please check if it passes tests, has adequate coverage, etc.
 ```bash
-make qa
+go test
+go test -cover
 ```

vendor/github.com/willf/bitset/bitset.go

@@ -138,6 +138,9 @@ func (b *BitSet) Len() uint {
 // extendSetMaybe adds additional words to incorporate new bits if needed
 func (b *BitSet) extendSetMaybe(i uint) {
 	if i >= b.length { // if we need more bits, make 'em
+		if i >= Cap() {
+			panic("You are exceeding the capacity")
+		}
 		nsize := wordsNeeded(i + 1)
 		if b.set == nil {
 			b.set = make([]uint64, nsize)
@@ -160,7 +163,12 @@ func (b *BitSet) Test(i uint) bool {
 	return b.set[i>>log2WordSize]&(1<<(i&(wordSize-1))) != 0
 }
 
-// Set bit i to 1
+// Set bit i to 1, the capacity of the bitset is automatically
+// increased accordingly.
+// If i>= Cap(), this function will panic.
+// Warning: using a very large value for 'i'
+// may lead to a memory shortage and a panic: the caller is responsible
+// for providing sensible parameters in line with their memory capacity.
 func (b *BitSet) Set(i uint) *BitSet {
 	b.extendSetMaybe(i)
 	b.set[i>>log2WordSize] |= 1 << (i & (wordSize - 1))
@@ -176,7 +184,11 @@ func (b *BitSet) Clear(i uint) *BitSet {
 	return b
 }
 
-// SetTo sets bit i to value
+// SetTo sets bit i to value.
+// If i>= Cap(), this function will panic.
+// Warning: using a very large value for 'i'
+// may lead to a memory shortage and a panic: the caller is responsible
+// for providing sensible parameters in line with their memory capacity.
 func (b *BitSet) SetTo(i uint, value bool) *BitSet {
 	if value {
 		return b.Set(i)
@@ -184,7 +196,11 @@ func (b *BitSet) SetTo(i uint, value bool) *BitSet {
 	return b.Clear(i)
 }
 
-// Flip bit at i
+// Flip bit at i.
+// If i>= Cap(), this function will panic.
+// Warning: using a very large value for 'i'
+// may lead to a memory shortage and a panic: the caller is responsible
+// for providing sensible parameters in line with their memory capacity.
 func (b *BitSet) Flip(i uint) *BitSet {
 	if i >= b.length {
 		return b.Set(i)
@@ -193,26 +209,51 @@ func (b *BitSet) Flip(i uint) *BitSet {
 	return b
 }
 
-// Shrink shrinks BitSet to desired length in bits. It clears all bits > length
+// Shrink shrinks BitSet so that the provided value is the last possible
-// and reduces the size and length of the set.
+// set value. It clears all bits > the provided index and reduces the size
+// and length of the set.
+//
+// Note that the parameter value is not the new length in bits: it is the
+// maximal value that can be stored in the bitset after the function call.
+// The new length in bits is the parameter value + 1. Thus it is not possible
+// to use this function to set the length to 0, the minimal value of the length
+// after this function call is 1.
 //
 // A new slice is allocated to store the new bits, so you may see an increase in
 // memory usage until the GC runs. Normally this should not be a problem, but if you
 // have an extremely large BitSet its important to understand that the old BitSet will
 // remain in memory until the GC frees it.
-func (b *BitSet) Shrink(length uint) *BitSet {
+func (b *BitSet) Shrink(lastbitindex uint) *BitSet {
-	idx := wordsNeeded(length + 1)
+	length := lastbitindex + 1
+	idx := wordsNeeded(length)
 	if idx > len(b.set) {
 		return b
 	}
 	shrunk := make([]uint64, idx)
 	copy(shrunk, b.set[:idx])
 	b.set = shrunk
-	b.length = length + 1
+	b.length = length
-	b.set[idx-1] &= (allBits >> (uint64(64) - uint64(length&(wordSize-1)) - 1))
+	b.set[idx-1] &= (allBits >> (uint64(64) - uint64(length&(wordSize-1))))
 	return b
 }
 
+// Compact shrinks BitSet to so that we preserve all set bits, while minimizing
+// memory usage. Compact calls Shrink.
+func (b *BitSet) Compact() *BitSet {
+	idx := len(b.set) - 1
+	for ; idx >= 0 && b.set[idx] == 0; idx-- {
+	}
+	newlength := uint((idx + 1) << log2WordSize)
+	if newlength >= b.length {
+		return b // nothing to do
+	}
+	if newlength > 0 {
+		return b.Shrink(newlength - 1)
+	}
+	// We preserve one word
+	return b.Shrink(63)
+}
+
 // InsertAt takes an index which indicates where a bit should be
 // inserted. Then it shifts all the bits in the set to the left by 1, starting
 // from the given index position, and sets the index position to 0.
@@ -323,6 +364,9 @@ func (b *BitSet) DeleteAt(i uint) *BitSet {
 // including possibly the current index
 // along with an error code (true = valid, false = no set bit found)
 // for i,e := v.NextSet(0); e; i,e = v.NextSet(i + 1) {...}
+//
+// Users concerned with performance may want to use NextSetMany to
+// retrieve several values at once.
 func (b *BitSet) NextSet(i uint) (uint, bool) {
 	x := int(i >> log2WordSize)
 	if x >= len(b.set) {
@@ -358,6 +402,14 @@ func (b *BitSet) NextSet(i uint) (uint, bool) {
 //     j += 1
 //    }
 //
+//
+// It is possible to retrieve all set bits as follow:
+//
+//    indices := make([]uint, bitmap.Count())
+//    bitmap.NextSetMany(0, indices)
+//
+// However if bitmap.Count() is large, it might be preferable to
+// use several calls to NextSetMany, for performance reasons.
 func (b *BitSet) NextSetMany(i uint, buffer []uint) (uint, []uint) {
 	myanswer := buffer
 	capacity := cap(buffer)
@@ -809,7 +861,7 @@ func (b *BitSet) ReadFrom(stream io.Reader) (int64, error) {
 	newset := New(uint(length))
 
 	if uint64(newset.length) != length {
-		return 0, errors.New("Unmarshalling error: type mismatch")
+		return 0, errors.New("unmarshalling error: type mismatch")
 	}
 
 	// Read remaining bytes as set

vendor/github.com/willf/bitset/go.mod

@@ -0,0 +1,3 @@
+module github.com/willf/bitset
+
+go 1.14

vendor/modules.txt

@@ -69,7 +69,8 @@ github.com/vishvananda/netlink
 github.com/vishvananda/netlink/nl
 # github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df
 github.com/vishvananda/netns
-# github.com/willf/bitset v1.1.11-0.20200630133818-d5bec3311243
+# github.com/willf/bitset v1.1.11
+## explicit
 github.com/willf/bitset
 # golang.org/x/sys v0.0.0-20200916030750-2334cc1a136f
 ## explicit