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|
package main
import (
"fmt"
"path/filepath"
"runtime"
"syscall"
"unsafe"
)
const (
sysRenameat2 = 316 // SYS_RENAMEAT2 on amd64
renameNoreplaceFlag = 1 // RENAME_NOREPLACE
)
// renameBasic creates a file and renames it via rename(2).
// Uses raw SYS_RENAME because Go's syscall.Rename wraps renameat on amd64.
func renameBasic() error {
dir, cleanup, err := makeTempDir("rename-basic")
if err != nil {
return err
}
defer cleanup()
oldPath := filepath.Join(dir, "oldname.txt")
newPath := filepath.Join(dir, "newname.txt")
fd, err := syscall.Open(oldPath, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
if err := syscall.Close(fd); err != nil {
return fmt.Errorf("close: %w", err)
}
oldBytes, err := syscall.BytePtrFromString(oldPath)
if err != nil {
return fmt.Errorf("old path bytes: %w", err)
}
newBytes, err := syscall.BytePtrFromString(newPath)
if err != nil {
return fmt.Errorf("new path bytes: %w", err)
}
_, _, errno := syscall.Syscall(
syscall.SYS_RENAME,
uintptr(unsafe.Pointer(oldBytes)),
uintptr(unsafe.Pointer(newBytes)),
0,
)
runtime.KeepAlive(oldBytes)
runtime.KeepAlive(newBytes)
if errno != 0 {
return fmt.Errorf("rename: %w", errno)
}
return nil
}
// renameRenameat creates a file and renames it via renameat(2).
func renameRenameat() error {
dir, cleanup, err := makeTempDir("rename-renameat")
if err != nil {
return err
}
defer cleanup()
oldName := "renameat-old.txt"
newName := "renameat-new.txt"
path := filepath.Join(dir, oldName)
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
if err := syscall.Close(fd); err != nil {
return fmt.Errorf("close: %w", err)
}
dirFD, err := syscall.Open(dir, syscall.O_RDONLY|syscall.O_DIRECTORY, 0)
if err != nil {
return fmt.Errorf("open dir: %w", err)
}
defer syscall.Close(dirFD)
oldBytes, err := syscall.BytePtrFromString(oldName)
if err != nil {
return fmt.Errorf("old name bytes: %w", err)
}
newBytes, err := syscall.BytePtrFromString(newName)
if err != nil {
return fmt.Errorf("new name bytes: %w", err)
}
_, _, errno := syscall.Syscall6(
syscall.SYS_RENAMEAT,
uintptr(dirFD),
uintptr(unsafe.Pointer(oldBytes)),
uintptr(dirFD),
uintptr(unsafe.Pointer(newBytes)),
0, 0,
)
runtime.KeepAlive(oldBytes)
runtime.KeepAlive(newBytes)
if errno != 0 {
return fmt.Errorf("renameat: %w", errno)
}
return nil
}
// renameRenameat2 creates a file and renames it via renameat2(2) with no flags.
func renameRenameat2() error {
dir, cleanup, err := makeTempDir("rename-renameat2")
if err != nil {
return err
}
defer cleanup()
oldName := "renameat2-old.txt"
newName := "renameat2-new.txt"
path := filepath.Join(dir, oldName)
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
if err := syscall.Close(fd); err != nil {
return fmt.Errorf("close: %w", err)
}
errno, err := doRenameat2(dir, oldName, newName, 0)
if err != nil {
return err
}
if errno != 0 {
return fmt.Errorf("renameat2: %w", errno)
}
return nil
}
// doRenameat2 opens dir as a directory fd, builds name byte pointers, calls
// renameat2(2) with the given flags, and returns the raw errno. Zero means
// success. It is shared by renameRenameat2 and renameNoreplace to avoid
// duplicating the dir-open + byte-pointer + syscall6 boilerplate.
func doRenameat2(dir, oldName, newName string, flags uintptr) (syscall.Errno, error) {
dirFD, err := syscall.Open(dir, syscall.O_RDONLY|syscall.O_DIRECTORY, 0)
if err != nil {
return 0, fmt.Errorf("open dir: %w", err)
}
defer syscall.Close(dirFD)
oldBytes, err := syscall.BytePtrFromString(oldName)
if err != nil {
return 0, fmt.Errorf("old name bytes: %w", err)
}
newBytes, err := syscall.BytePtrFromString(newName)
if err != nil {
return 0, fmt.Errorf("new name bytes: %w", err)
}
_, _, errno := syscall.Syscall6(
sysRenameat2,
uintptr(dirFD),
uintptr(unsafe.Pointer(oldBytes)),
uintptr(dirFD),
uintptr(unsafe.Pointer(newBytes)),
flags,
0,
)
runtime.KeepAlive(oldBytes)
runtime.KeepAlive(newBytes)
return errno, nil
}
// renameEnoent attempts to rename a nonexistent file via raw SYS_RENAME.
// The syscall fails with ENOENT, but ior captures the tracepoint on entry.
func renameEnoent() error {
dir, cleanup, err := makeTempDir("rename-enoent")
if err != nil {
return err
}
defer cleanup()
oldPath := filepath.Join(dir, "rename-enoent-missing.txt")
newPath := filepath.Join(dir, "rename-enoent-new.txt")
oldBytes, err := syscall.BytePtrFromString(oldPath)
if err != nil {
return fmt.Errorf("old path bytes: %w", err)
}
newBytes, err := syscall.BytePtrFromString(newPath)
if err != nil {
return fmt.Errorf("new path bytes: %w", err)
}
for i := 0; i < 5; i++ {
_, _, errno := syscall.Syscall(
syscall.SYS_RENAME,
uintptr(unsafe.Pointer(oldBytes)),
uintptr(unsafe.Pointer(newBytes)),
0,
)
runtime.KeepAlive(oldBytes)
runtime.KeepAlive(newBytes)
if errno == 0 {
return fmt.Errorf("expected ENOENT, but rename succeeded")
}
}
return nil
}
// renameNoreplace creates two files, then attempts renameat2 with
// RENAME_NOREPLACE. Because the target already exists, the syscall fails
// with EEXIST, but ior captures the tracepoint on entry.
func renameNoreplace() error {
dir, cleanup, err := makeTempDir("rename-noreplace")
if err != nil {
return err
}
defer cleanup()
srcName := "noreplace-src.txt"
dstName := "noreplace-dst.txt"
for _, name := range []string{srcName, dstName} {
path := filepath.Join(dir, name)
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("create %s: %w", name, err)
}
if err := syscall.Close(fd); err != nil {
return fmt.Errorf("close %s: %w", name, err)
}
}
errno, err := doRenameat2(dir, srcName, dstName, renameNoreplaceFlag)
if err != nil {
return err
}
if errno == 0 {
return fmt.Errorf("expected EEXIST, but renameat2 NOREPLACE succeeded")
}
return nil
}
|
