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package internal
import (
"errors"
"fmt"
"sync"
)
// ErrNotSupported indicates that a feature is not supported by the current kernel.
var ErrNotSupported = errors.New("not supported")
// UnsupportedFeatureError is returned by FeatureTest() functions.
type UnsupportedFeatureError struct {
// The minimum Linux mainline version required for this feature.
// Used for the error string, and for sanity checking during testing.
MinimumVersion Version
// The name of the feature that isn't supported.
Name string
}
func (ufe *UnsupportedFeatureError) Error() string {
if ufe.MinimumVersion.Unspecified() {
return fmt.Sprintf("%s not supported", ufe.Name)
}
return fmt.Sprintf("%s not supported (requires >= %s)", ufe.Name, ufe.MinimumVersion)
}
// Is indicates that UnsupportedFeatureError is ErrNotSupported.
func (ufe *UnsupportedFeatureError) Is(target error) bool {
return target == ErrNotSupported
}
type featureTest struct {
sync.RWMutex
successful bool
result error
}
// FeatureTestFn is used to determine whether the kernel supports
// a certain feature.
//
// The return values have the following semantics:
//
// err == ErrNotSupported: the feature is not available
// err == nil: the feature is available
// err != nil: the test couldn't be executed
type FeatureTestFn func() error
// FeatureTest wraps a function so that it is run at most once.
//
// name should identify the tested feature, while version must be in the
// form Major.Minor[.Patch].
//
// Returns an error wrapping ErrNotSupported if the feature is not supported.
func FeatureTest(name, version string, fn FeatureTestFn) func() error {
v, err := NewVersion(version)
if err != nil {
return func() error { return err }
}
ft := new(featureTest)
return func() error {
ft.RLock()
if ft.successful {
defer ft.RUnlock()
return ft.result
}
ft.RUnlock()
ft.Lock()
defer ft.Unlock()
// check one more time on the off
// chance that two go routines
// were able to call into the write
// lock
if ft.successful {
return ft.result
}
err := fn()
switch {
case errors.Is(err, ErrNotSupported):
ft.result = &UnsupportedFeatureError{
MinimumVersion: v,
Name: name,
}
fallthrough
case err == nil:
ft.successful = true
default:
// We couldn't execute the feature test to a point
// where it could make a determination.
// Don't cache the result, just return it.
return fmt.Errorf("detect support for %s: %w", name, err)
}
return ft.result
}
}
// A Version in the form Major.Minor.Patch.
type Version [3]uint16
// NewVersion creates a version from a string like "Major.Minor.Patch".
//
// Patch is optional.
func NewVersion(ver string) (Version, error) {
var major, minor, patch uint16
n, _ := fmt.Sscanf(ver, "%d.%d.%d", &major, &minor, &patch)
if n < 2 {
return Version{}, fmt.Errorf("invalid version: %s", ver)
}
return Version{major, minor, patch}, nil
}
func (v Version) String() string {
if v[2] == 0 {
return fmt.Sprintf("v%d.%d", v[0], v[1])
}
return fmt.Sprintf("v%d.%d.%d", v[0], v[1], v[2])
}
// Less returns true if the version is less than another version.
func (v Version) Less(other Version) bool {
for i, a := range v {
if a == other[i] {
continue
}
return a < other[i]
}
return false
}
// Unspecified returns true if the version is all zero.
func (v Version) Unspecified() bool {
return v[0] == 0 && v[1] == 0 && v[2] == 0
}
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