syscallcompat: build emulated syscalls under linux, too

This will allow to test them under linux as well.

2 files changed, 213 insertions, 164 deletions

diff --git a/internal/syscallcompat/emulate.go b/internal/syscallcompat/emulate.go
new file mode 100644
index 0000000..6cb0ea0
--- /dev/null
+++ b/internal/syscallcompat/emulate.go
@@ -0,0 +1,193 @@
+package syscallcompat
+
+import (
+	"os"
+	"path/filepath"
+	"sync"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+var chdirMutex sync.Mutex
+
+// emulateOpenat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateOpenat(dirfd int, path string, flags int, mode uint32) (int, error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	if !filepath.IsAbs(path) {
+		// Save the old working directory
+		oldWd, err := os.Getwd()
+		if err != nil {
+			return -1, err
+		}
+		// Chdir to target directory
+		err = syscall.Fchdir(dirfd)
+		if err != nil {
+			return -1, err
+		}
+		// Chdir back at the end
+		defer os.Chdir(oldWd)
+	}
+	return syscall.Open(path, flags, mode)
+}
+
+// emulateRenameat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateRenameat(olddirfd int, oldpath string, newdirfd int, newpath string) error {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	// Unless both paths are absolute we have to save the old working dir and
+	// Chdir(oldWd) back to it in the end. If we error out before the first
+	// chdir, Chdir(oldWd) is unneccassary but does no harm.
+	if !filepath.IsAbs(oldpath) || !filepath.IsAbs(newpath) {
+		oldWd, err := os.Getwd()
+		if err != nil {
+			return err
+		}
+		defer os.Chdir(oldWd)
+	}
+	// Make oldpath absolute
+	oldpath, err := dirfdAbs(olddirfd, oldpath)
+	if err != nil {
+		return err
+	}
+	// Make newpath absolute
+	newpath, err = dirfdAbs(newdirfd, newpath)
+	if err != nil {
+		return err
+	}
+	return syscall.Rename(oldpath, newpath)
+}
+
+// emulateUnlinkat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateUnlinkat(dirfd int, path string, flags int) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(cwd)
+	err = syscall.Fchdir(dirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	if (flags & unix.AT_REMOVEDIR) != 0 {
+		return syscall.Rmdir(path)
+	} else {
+		return syscall.Unlink(path)
+	}
+}
+
+// emulateMknodat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateMknodat(dirfd int, path string, mode uint32, dev int) error {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	if !filepath.IsAbs(path) {
+		oldWd, err := os.Getwd()
+		if err != nil {
+			return err
+		}
+		defer os.Chdir(oldWd)
+	}
+	path, err := dirfdAbs(dirfd, path)
+	if err != nil {
+		return err
+	}
+	return syscall.Mknod(path, mode, dev)
+}
+
+// dirfdAbs transforms the dirfd-relative "path" to an absolute one. If the
+// path is not already absolute, this function will change the working
+// directory. The caller has to chdir back.
+func dirfdAbs(dirfd int, path string) (string, error) {
+	if filepath.IsAbs(path) {
+		return path, nil
+	}
+	err := syscall.Fchdir(dirfd)
+	if err != nil {
+		return "", err
+	}
+	wd, err := os.Getwd()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(wd, path), nil
+}
+
+// emulateFchmodat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateFchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(cwd)
+	err = syscall.Fchdir(dirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	return syscall.Chmod(path, mode)
+}
+
+// emulateFchownat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateFchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(cwd)
+	err = syscall.Fchdir(dirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	return syscall.Lchown(path, uid, gid)
+}
+
+// emulateSymlinkat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateSymlinkat(oldpath string, newdirfd int, newpath string) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(cwd)
+	err = syscall.Fchdir(newdirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	return syscall.Symlink(oldpath, newpath)
+}
+
+// emulateMkdirat emulates the syscall for platforms that don't have it
+// in the kernel (darwin).
+func emulateMkdirat(dirfd int, path string, mode uint32) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(cwd)
+	err = syscall.Fchdir(dirfd)
+	if err != nil {
+		return err
+	}
+	defer syscall.Fchdir(cwd)
+	return syscall.Mkdir(path, mode)
+}
diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index 39a225f..6238940 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -2,12 +2,7 @@ package syscallcompat
 
 import (
 	"log"
-	"os"
-	"path/filepath"
-	"sync"
 	"syscall"
-
-	"golang.org/x/sys/unix"
 )
 
 // Sorry, fallocate is not available on OSX at all and
@@ -22,185 +17,46 @@ func Fallocate(fd int, mode uint32, off int64, len int64) error {
 	return syscall.EOPNOTSUPP
 }
 
-var chdirMutex sync.Mutex
-
-// Poor man's Openat
-func Openat(dirfd int, path string, flags int, mode uint32) (int, error) {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	if !filepath.IsAbs(path) {
-		// Save the old working directory
-		oldWd, err := os.Getwd()
-		if err != nil {
-			return -1, err
-		}
-		// Chdir to target directory
-		err = syscall.Fchdir(dirfd)
-		if err != nil {
-			return -1, err
-		}
-		// Chdir back at the end
-		defer os.Chdir(oldWd)
+// Dup3 is not available on Darwin, so we use Dup2 instead.
+func Dup3(oldfd int, newfd int, flags int) (err error) {
+	if flags != 0 {
+		log.Panic("darwin does not support dup3 flags")
 	}
-	return syscall.Open(path, flags, mode)
+	return syscall.Dup2(oldfd, newfd)
 }
 
-// Poor man's Renameat
-func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) error {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	// Unless both paths are absolute we have to save the old working dir and
-	// Chdir(oldWd) back to it in the end. If we error out before the first
-	// chdir, Chdir(oldWd) is unneccassary but does no harm.
-	if !filepath.IsAbs(oldpath) || !filepath.IsAbs(newpath) {
-		oldWd, err := os.Getwd()
-		if err != nil {
-			return err
-		}
-		defer os.Chdir(oldWd)
-	}
-	// Make oldpath absolute
-	oldpath, err := dirfdAbs(olddirfd, oldpath)
-	if err != nil {
-		return err
-	}
-	// Make newpath absolute
-	newpath, err = dirfdAbs(newdirfd, newpath)
-	if err != nil {
-		return err
-	}
-	return syscall.Rename(oldpath, newpath)
-}
+////////////////////////////////////////////////////////
+//// Emulated Syscalls (see emulate.go) ////////////////
+////////////////////////////////////////////////////////
 
-// Poor man's Unlinkat
-func Unlinkat(dirfd int, path string, flags int) (err error) {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
-	if err != nil {
-		return err
-	}
-	defer syscall.Close(cwd)
-	err = syscall.Fchdir(dirfd)
-	if err != nil {
-		return err
-	}
-	defer syscall.Fchdir(cwd)
-	if (flags & unix.AT_REMOVEDIR) != 0 {
-		return syscall.Rmdir(path)
-	} else {
-		return syscall.Unlink(path)
-	}
+func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
+	return emulateOpenat(dirfd, path, flags, mode)
 }
 
-// Poor man's Mknodat
-func Mknodat(dirfd int, path string, mode uint32, dev int) error {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	if !filepath.IsAbs(path) {
-		oldWd, err := os.Getwd()
-		if err != nil {
-			return err
-		}
-		defer os.Chdir(oldWd)
-	}
-	path, err := dirfdAbs(dirfd, path)
-	if err != nil {
-		return err
-	}
-	return syscall.Mknod(path, mode, dev)
+func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error) {
+	return emulateRenameat(olddirfd, oldpath, newdirfd, newpath)
 }
 
-// dirfdAbs transforms the dirfd-relative "path" to an absolute one. If the
-// path is not already absolute, this function will change the working
-// directory. The caller has to chdir back.
-func dirfdAbs(dirfd int, path string) (string, error) {
-	if filepath.IsAbs(path) {
-		return path, nil
-	}
-	err := syscall.Fchdir(dirfd)
-	if err != nil {
-		return "", err
-	}
-	wd, err := os.Getwd()
-	if err != nil {
-		return "", err
-	}
-	return filepath.Join(wd, path), nil
+func Unlinkat(dirfd int, path string, flags int) (err error) {
+	return emulateUnlinkat(dirfd, path, flags)
 }
 
-// Dup3 is not available on Darwin, so we use Dup2 instead.
-func Dup3(oldfd int, newfd int, flags int) (err error) {
-	if flags != 0 {
-		log.Panic("darwin does not support dup3 flags")
-	}
-	return syscall.Dup2(oldfd, newfd)
+func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
+	return emulateMknodat(dirfd, path, mode, dev)
 }
 
-// Poor man's Fchmodat.
 func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
-	if err != nil {
-		return err
-	}
-	defer syscall.Close(cwd)
-	err = syscall.Fchdir(dirfd)
-	if err != nil {
-		return err
-	}
-	defer syscall.Fchdir(cwd)
-	return syscall.Chmod(path, mode)
+	return emulateFchmodat(dirfd, path, mode, flags)
 }
 
-// Poor man's Fchownat.
 func Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
-	if err != nil {
-		return err
-	}
-	defer syscall.Close(cwd)
-	err = syscall.Fchdir(dirfd)
-	if err != nil {
-		return err
-	}
-	defer syscall.Fchdir(cwd)
-	return syscall.Lchown(path, uid, gid)
+	return emulateFchownat(dirfd, path, uid, gid, flags)
 }
 
-// Poor man's Symlinkat.
 func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
-	if err != nil {
-		return err
-	}
-	defer syscall.Close(cwd)
-	err = syscall.Fchdir(newdirfd)
-	if err != nil {
-		return err
-	}
-	defer syscall.Fchdir(cwd)
-	return syscall.Symlink(oldpath, newpath)
+	return emulateSymlinkat(oldpath, newdirfd, newpath)
 }
 
-// Poor man's Mkdirat.
 func Mkdirat(dirfd int, path string, mode uint32) (err error) {
-	chdirMutex.Lock()
-	defer chdirMutex.Unlock()
-	cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
-	if err != nil {
-		return err
-	}
-	defer syscall.Close(cwd)
-	err = syscall.Fchdir(dirfd)
-	if err != nil {
-		return err
-	}
-	defer syscall.Fchdir(cwd)
-	return syscall.Mkdir(path, mode)
+	return emulateMkdirat(dirfd, path, mode)
 }