[syserr] Covert all linuxerr returns to error type.

Change the linuxerr.ErrorFromErrno to return an error type and not
a *errors.Error type. The latter results in problems comparing to nil
as <nil><nil> != <nil><*errors.Error>.

In a follow up, there will be a change to remove *errors.Error.Errno(),
which will also encourage users to not use Errnos to reference linuxerr.

PiperOrigin-RevId: 406444419

3 files changed, 79 insertions, 67 deletions

diff --git a/pkg/errors/linuxerr/BUILD b/pkg/errors/linuxerr/BUILD
index e73b0e28a..5b59ebd6e 100644
--- a/pkg/errors/linuxerr/BUILD
+++ b/pkg/errors/linuxerr/BUILD
@@ -21,7 +21,6 @@ go_test(
     srcs = ["linuxerr_test.go"],
     deps = [
         ":linuxerr",
-        "//pkg/abi/linux/errno",
         "//pkg/errors",
         "@org_golang_x_sys//unix:go_default_library",
     ],
diff --git a/pkg/errors/linuxerr/linuxerr.go b/pkg/errors/linuxerr/linuxerr.go
index 5905ef593..e44a55afd 100644
--- a/pkg/errors/linuxerr/linuxerr.go
+++ b/pkg/errors/linuxerr/linuxerr.go
@@ -34,41 +34,41 @@ const maxErrno uint32 = errno.EHWPOISON + 1
 // (e.g. unix.Errno(EPERM.Errno()) == unix.EPERM is true). Converting unix/syscall.Errno
 // to the errors should be done via the lookup methods provided.
 var (
-	NOERROR = errors.New(errno.NOERRNO, "not an error")
-	EPERM   = errors.New(errno.EPERM, "operation not permitted")
-	ENOENT  = errors.New(errno.ENOENT, "no such file or directory")
-	ESRCH   = errors.New(errno.ESRCH, "no such process")
-	EINTR   = errors.New(errno.EINTR, "interrupted system call")
-	EIO     = errors.New(errno.EIO, "I/O error")
-	ENXIO   = errors.New(errno.ENXIO, "no such device or address")
-	E2BIG   = errors.New(errno.E2BIG, "argument list too long")
-	ENOEXEC = errors.New(errno.ENOEXEC, "exec format error")
-	EBADF   = errors.New(errno.EBADF, "bad file number")
-	ECHILD  = errors.New(errno.ECHILD, "no child processes")
-	EAGAIN  = errors.New(errno.EAGAIN, "try again")
-	ENOMEM  = errors.New(errno.ENOMEM, "out of memory")
-	EACCES  = errors.New(errno.EACCES, "permission denied")
-	EFAULT  = errors.New(errno.EFAULT, "bad address")
-	ENOTBLK = errors.New(errno.ENOTBLK, "block device required")
-	EBUSY   = errors.New(errno.EBUSY, "device or resource busy")
-	EEXIST  = errors.New(errno.EEXIST, "file exists")
-	EXDEV   = errors.New(errno.EXDEV, "cross-device link")
-	ENODEV  = errors.New(errno.ENODEV, "no such device")
-	ENOTDIR = errors.New(errno.ENOTDIR, "not a directory")
-	EISDIR  = errors.New(errno.EISDIR, "is a directory")
-	EINVAL  = errors.New(errno.EINVAL, "invalid argument")
-	ENFILE  = errors.New(errno.ENFILE, "file table overflow")
-	EMFILE  = errors.New(errno.EMFILE, "too many open files")
-	ENOTTY  = errors.New(errno.ENOTTY, "not a typewriter")
-	ETXTBSY = errors.New(errno.ETXTBSY, "text file busy")
-	EFBIG   = errors.New(errno.EFBIG, "file too large")
-	ENOSPC  = errors.New(errno.ENOSPC, "no space left on device")
-	ESPIPE  = errors.New(errno.ESPIPE, "illegal seek")
-	EROFS   = errors.New(errno.EROFS, "read-only file system")
-	EMLINK  = errors.New(errno.EMLINK, "too many links")
-	EPIPE   = errors.New(errno.EPIPE, "broken pipe")
-	EDOM    = errors.New(errno.EDOM, "math argument out of domain of func")
-	ERANGE  = errors.New(errno.ERANGE, "math result not representable")
+	noError *errors.Error = nil
+	EPERM                 = errors.New(errno.EPERM, "operation not permitted")
+	ENOENT                = errors.New(errno.ENOENT, "no such file or directory")
+	ESRCH                 = errors.New(errno.ESRCH, "no such process")
+	EINTR                 = errors.New(errno.EINTR, "interrupted system call")
+	EIO                   = errors.New(errno.EIO, "I/O error")
+	ENXIO                 = errors.New(errno.ENXIO, "no such device or address")
+	E2BIG                 = errors.New(errno.E2BIG, "argument list too long")
+	ENOEXEC               = errors.New(errno.ENOEXEC, "exec format error")
+	EBADF                 = errors.New(errno.EBADF, "bad file number")
+	ECHILD                = errors.New(errno.ECHILD, "no child processes")
+	EAGAIN                = errors.New(errno.EAGAIN, "try again")
+	ENOMEM                = errors.New(errno.ENOMEM, "out of memory")
+	EACCES                = errors.New(errno.EACCES, "permission denied")
+	EFAULT                = errors.New(errno.EFAULT, "bad address")
+	ENOTBLK               = errors.New(errno.ENOTBLK, "block device required")
+	EBUSY                 = errors.New(errno.EBUSY, "device or resource busy")
+	EEXIST                = errors.New(errno.EEXIST, "file exists")
+	EXDEV                 = errors.New(errno.EXDEV, "cross-device link")
+	ENODEV                = errors.New(errno.ENODEV, "no such device")
+	ENOTDIR               = errors.New(errno.ENOTDIR, "not a directory")
+	EISDIR                = errors.New(errno.EISDIR, "is a directory")
+	EINVAL                = errors.New(errno.EINVAL, "invalid argument")
+	ENFILE                = errors.New(errno.ENFILE, "file table overflow")
+	EMFILE                = errors.New(errno.EMFILE, "too many open files")
+	ENOTTY                = errors.New(errno.ENOTTY, "not a typewriter")
+	ETXTBSY               = errors.New(errno.ETXTBSY, "text file busy")
+	EFBIG                 = errors.New(errno.EFBIG, "file too large")
+	ENOSPC                = errors.New(errno.ENOSPC, "no space left on device")
+	ESPIPE                = errors.New(errno.ESPIPE, "illegal seek")
+	EROFS                 = errors.New(errno.EROFS, "read-only file system")
+	EMLINK                = errors.New(errno.EMLINK, "too many links")
+	EPIPE                 = errors.New(errno.EPIPE, "broken pipe")
+	EDOM                  = errors.New(errno.EDOM, "math argument out of domain of func")
+	ERANGE                = errors.New(errno.ERANGE, "math result not representable")
 
 	// Errno values from include/uapi/asm-generic/errno.h.
 	EDEADLK         = errors.New(errno.EDEADLK, "resource deadlock would occur")
@@ -186,7 +186,7 @@ var errNotValidError = errors.New(errno.Errno(maxErrno), "not a valid error")
 // errnos (especially uint32(sycall.Errno)) and *errors.Error.
 var errorSlice = []*errors.Error{
 	// Errno values from include/uapi/asm-generic/errno-base.h.
-	errno.NOERRNO: NOERROR,
+	errno.NOERRNO: noError,
 	errno.EPERM:   EPERM,
 	errno.ENOENT:  ENOENT,
 	errno.ESRCH:   ESRCH,
@@ -324,32 +324,45 @@ var errorSlice = []*errors.Error{
 	errno.EHWPOISON:       EHWPOISON,
 }
 
-// ErrorFromErrno gets an error from the list and panics if an invalid entry is requested.
-func ErrorFromErrno(e errno.Errno) *errors.Error {
-	err := errorSlice[e]
+// ErrorFromUnix returns a linuxerr from a unix.Errno.
+func ErrorFromUnix(err unix.Errno) error {
+	if err == unix.Errno(0) {
+		return nil
+	}
+	e := errorSlice[errno.Errno(err)]
 	// Done this way because a single comparison in benchmarks is 2-3 faster
 	// than something like ( if err == nil && err > 0 ).
-	if err != errNotValidError {
-		return err
+	if e == errNotValidError {
+		panic(fmt.Sprintf("invalid error requested with errno: %v", e))
 	}
-	panic(fmt.Sprintf("invalid error requested with errno: %d", e))
+	return e
 }
 
-// Equals compars a linuxerr to a given error
-// TODO(b/34162363): Remove when syserror is removed.
-func Equals(e *errors.Error, err error) bool {
-	if err == nil {
-		return e == NOERROR || e == nil
+// ToError converts a linuxerr to an error type.
+func ToError(err *errors.Error) error {
+	if err == noError {
+		return nil
 	}
-	if e == nil {
-		return err == NOERROR || err == unix.Errno(0)
+	return err
+}
+
+// ToUnix converts a linuxerr to a unix.Errno.
+func ToUnix(e *errors.Error) unix.Errno {
+	var unixErr unix.Errno
+	if e != noError {
+		unixErr = unix.Errno(e.Errno())
 	}
+	return unixErr
+}
 
-	switch err.(type) {
-	case *errors.Error:
-		return e == err
-	case unix.Errno, error:
-		return unix.Errno(e.Errno()) == err
+// Equals compars a linuxerr to a given error.
+func Equals(e *errors.Error, err error) bool {
+	var unixErr unix.Errno
+	if e != noError {
+		unixErr = unix.Errno(e.Errno())
+	}
+	if err == nil {
+		err = noError
 	}
-	return false
+	return e == err || unixErr == err
 }
diff --git a/pkg/errors/linuxerr/linuxerr_test.go b/pkg/errors/linuxerr/linuxerr_test.go
index df7cd1c5a..b99884b22 100644
--- a/pkg/errors/linuxerr/linuxerr_test.go
+++ b/pkg/errors/linuxerr/linuxerr_test.go
@@ -23,7 +23,6 @@ import (
 	"testing"
 
 	"golang.org/x/sys/unix"
-	"gvisor.dev/gvisor/pkg/abi/linux/errno"
 	gErrors "gvisor.dev/gvisor/pkg/errors"
 	"gvisor.dev/gvisor/pkg/errors/linuxerr"
 )
@@ -121,7 +120,7 @@ func BenchmarkReturnLinuxerr(b *testing.B) {
 func BenchmarkConvertUnixLinuxerr(b *testing.B) {
 	var localError error
 	for i := b.N; i > 0; i-- {
-		localError = linuxerr.ErrorFromErrno(errno.Errno(unix.EINVAL))
+		localError = linuxerr.ErrorFromUnix(unix.EINVAL)
 	}
 	if localError != nil {
 		return
@@ -131,7 +130,7 @@ func BenchmarkConvertUnixLinuxerr(b *testing.B) {
 func BenchmarkConvertUnixLinuxerrZero(b *testing.B) {
 	var localError error
 	for i := b.N; i > 0; i-- {
-		localError = linuxerr.ErrorFromErrno(errno.Errno(0))
+		localError = linuxerr.ErrorFromUnix(unix.Errno(0))
 	}
 	if localError != nil {
 		return
@@ -179,7 +178,7 @@ func TestErrorTranslation(t *testing.T) {
 func TestSyscallErrnoToErrors(t *testing.T) {
 	for _, tc := range []struct {
 		errno syscall.Errno
-		err   *gErrors.Error
+		err   error
 	}{
 		{errno: syscall.EACCES, err: linuxerr.EACCES},
 		{errno: syscall.EAGAIN, err: linuxerr.EAGAIN},
@@ -200,9 +199,9 @@ func TestSyscallErrnoToErrors(t *testing.T) {
 		{errno: syscall.EWOULDBLOCK, err: linuxerr.EAGAIN},
 	} {
 		t.Run(tc.errno.Error(), func(t *testing.T) {
-			e := linuxerr.ErrorFromErrno(errno.Errno(tc.errno))
+			e := linuxerr.ErrorFromUnix(unix.Errno(tc.errno))
 			if e != tc.err {
-				t.Fatalf("Mismatch errors: want: %+v (%d) got: %+v %d", tc.err, tc.err.Errno(), e, e.Errno())
+				t.Fatalf("Mismatch errors: want: %+v %T got: %+v %T", tc.err, tc.err, e, e)
 			}
 		})
 	}
@@ -212,6 +211,7 @@ func TestSyscallErrnoToErrors(t *testing.T) {
 // unix.Errno and linuxerr.
 // TODO (b/34162363): Remove this.
 func TestEqualsMethod(t *testing.T) {
+	noError := linuxerr.ErrorFromUnix(unix.Errno(0))
 	for _, tc := range []struct {
 		name     string
 		linuxErr []*gErrors.Error
@@ -220,20 +220,20 @@ func TestEqualsMethod(t *testing.T) {
 	}{
 		{
 			name:     "compare nil",
-			linuxErr: []*gErrors.Error{nil, linuxerr.NOERROR},
-			err:      []error{nil, linuxerr.NOERROR, unix.Errno(0)},
+			linuxErr: []*gErrors.Error{nil},
+			err:      []error{nil, noError, unix.Errno(0)},
 			equal:    true,
 		},
 		{
 			name:     "linuxerr nil error not",
-			linuxErr: []*gErrors.Error{nil, linuxerr.NOERROR},
+			linuxErr: []*gErrors.Error{nil},
 			err:      []error{unix.Errno(1), linuxerr.EPERM, linuxerr.EACCES},
 			equal:    false,
 		},
 		{
 			name:     "linuxerr not nil error nil",
 			linuxErr: []*gErrors.Error{linuxerr.ENOENT},
-			err:      []error{nil, unix.Errno(0), linuxerr.NOERROR},
+			err:      []error{nil, unix.Errno(0)},
 			equal:    false,
 		},
 		{
@@ -250,7 +250,7 @@ func TestEqualsMethod(t *testing.T) {
 		},
 		{
 			name:     "other error",
-			linuxErr: []*gErrors.Error{nil, linuxerr.NOERROR, linuxerr.E2BIG, linuxerr.EINVAL},
+			linuxErr: []*gErrors.Error{nil, linuxerr.E2BIG, linuxerr.EINVAL},
 			err:      []error{fs.ErrInvalid, io.EOF},
 			equal:    false,
 		},