Add runc features command

Fix issue 3274

See `types/features/features.go`.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

libcontainer/seccomp/config.go

@@ -2,6 +2,7 @@ package seccomp
 
 import (
 	"fmt"
+	"sort"
 
 	"github.com/opencontainers/runc/libcontainer/configs"
 )
@@ -16,6 +17,17 @@ var operators = map[string]configs.Operator{
 	"SCMP_CMP_MASKED_EQ": configs.MaskEqualTo,
 }
 
+// KnownOperators returns the list of the known operations.
+// Used by `runc features`.
+func KnownOperators() []string {
+	var res []string
+	for k := range operators {
+		res = append(res, k)
+	}
+	sort.Strings(res)
+	return res
+}
+
 var actions = map[string]configs.Action{
 	"SCMP_ACT_KILL":   configs.Kill,
 	"SCMP_ACT_ERRNO":  configs.Errno,
@@ -26,6 +38,17 @@ var actions = map[string]configs.Action{
 	"SCMP_ACT_NOTIFY": configs.Notify,
 }
 
+// KnownActions returns the list of the known actions.
+// Used by `runc features`.
+func KnownActions() []string {
+	var res []string
+	for k := range actions {
+		res = append(res, k)
+	}
+	sort.Strings(res)
+	return res
+}
+
 var archs = map[string]string{
 	"SCMP_ARCH_X86":         "x86",
 	"SCMP_ARCH_X86_64":      "amd64",
@@ -45,6 +68,17 @@ var archs = map[string]string{
 	"SCMP_ARCH_S390X":       "s390x",
 }
 
+// KnownArchs returns the list of the known archs.
+// Used by `runc features`.
+func KnownArchs() []string {
+	var res []string
+	for k := range archs {
+		res = append(res, k)
+	}
+	sort.Strings(res)
+	return res
+}
+
 // ConvertStringToOperator converts a string into a Seccomp comparison operator.
 // Comparison operators use the names they are assigned by Libseccomp's header.
 // Attempting to convert a string that is not a valid operator results in an

libcontainer/seccomp/seccomp_linux.go

@@ -265,3 +265,6 @@ func matchCall(filter *libseccomp.ScmpFilter, call *configs.Syscall, defAct libs
 func Version() (uint, uint, uint) {
 	return libseccomp.GetLibraryVersion()
 }
+
+// Enabled is true if seccomp support is compiled in.
+const Enabled = true

libcontainer/seccomp/seccomp_unsupported.go

@@ -23,3 +23,6 @@ func InitSeccomp(config *configs.Seccomp) (int, error) {
 func Version() (uint, uint, uint) {
 	return 0, 0, 0
 }
+
+// Enabled is true if seccomp support is compiled in.
+const Enabled = false