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package container
import (
"errors"
"os"
"syscall"
"hakurei.app/container/vfs"
)
// messageFromError returns a printable error message for a supported concrete type.
func messageFromError(err error) (string, bool) {
if m, ok := messagePrefixP[MountError]("cannot ", err); ok {
return m, ok
}
if m, ok := messagePrefixP[os.PathError]("cannot ", err); ok {
return m, ok
}
if m, ok := messagePrefixP[AbsoluteError]("", err); ok {
return m, ok
}
if m, ok := messagePrefix[OpRepeatError]("", err); ok {
return m, ok
}
if m, ok := messagePrefix[OpStateError]("", err); ok {
return m, ok
}
if m, ok := messagePrefixP[vfs.DecoderError]("cannot ", err); ok {
return m, ok
}
if m, ok := messagePrefix[TmpfsSizeError]("", err); ok {
return m, ok
}
return zeroString, false
}
// messagePrefix checks and prefixes the error message of a non-pointer error.
// While this is usable for pointer errors, such use should be avoided as nil check is omitted.
func messagePrefix[T error](prefix string, err error) (string, bool) {
var targetError T
if errors.As(err, &targetError) {
return prefix + targetError.Error(), true
}
return zeroString, false
}
// messagePrefixP checks and prefixes the error message of a pointer error.
func messagePrefixP[V any, T interface {
*V
error
}](prefix string, err error) (string, bool) {
var targetError T
if errors.As(err, &targetError) && targetError != nil {
return prefix + targetError.Error(), true
}
return zeroString, false
}
type MountError struct {
Source, Target, Fstype string
Flags uintptr
Data string
syscall.Errno
}
func (e *MountError) Unwrap() error {
if e.Errno == 0 {
return nil
}
return e.Errno
}
func (e *MountError) Error() string {
if e.Flags&syscall.MS_BIND != 0 {
if e.Flags&syscall.MS_REMOUNT != 0 {
return "remount " + e.Target + ": " + e.Errno.Error()
}
return "bind " + e.Source + " on " + e.Target + ": " + e.Errno.Error()
}
if e.Fstype != FstypeNULL {
return "mount " + e.Fstype + " on " + e.Target + ": " + e.Errno.Error()
}
// fallback case: if this is reached, the conditions for it to occur should be handled above
return "mount " + e.Target + ": " + e.Errno.Error()
}
// errnoFallback returns the concrete errno from an error, or a [os.PathError] fallback.
func errnoFallback(op, path string, err error) (syscall.Errno, *os.PathError) {
var errno syscall.Errno
if !errors.As(err, &errno) {
return 0, &os.PathError{Op: op, Path: path, Err: err}
}
return errno, nil
}
// mount wraps syscall.Mount for error handling.
func mount(source, target, fstype string, flags uintptr, data string) error {
err := syscall.Mount(source, target, fstype, flags, data)
if err == nil {
return nil
}
if errno, pathError := errnoFallback("mount", target, err); pathError != nil {
return pathError
} else {
return &MountError{source, target, fstype, flags, data, errno}
}
}
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