syscallcompat: OSX: add Fallocate and Openat wrappers

...and convert all calls to syscall.{Fallocate,Openat}
to syscallcompat .

Both syscalls are not available on OSX. We emulate Openat and just
return EOPNOTSUPP for Fallocate.

1 files changed, 33 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index d437170..81e1b15 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -1,5 +1,11 @@
 package syscallcompat
 
+import (
+	"os"
+	"sync"
+	"syscall"
+)
+
 // prealloc - preallocate space without changing the file size. This prevents
 // us from running out of space in the middle of an operation.
 func Prealloc(fd int, off int64, len int64) (err error) {
@@ -10,3 +16,30 @@ func Prealloc(fd int, off int64, len int64) (err error) {
 	// See https://github.com/rfjakob/gocryptfs/issues/18 if you want to help.
 	return nil
 }
+
+var openatLock sync.Mutex
+
+// Poor man's Openat:
+// 1) fchdir to the dirfd
+// 2) open the file
+// 3) chdir back.
+func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
+	openatLock.Lock()
+	defer openatLock.Unlock()
+
+	oldWd, err := os.Getwd()
+	if err != nil {
+		return -1, err
+	}
+	err = syscall.Fchdir(dirfd)
+	if err != nil {
+		return -1, err
+	}
+	defer os.Chdir(oldWd)
+
+	return syscall.Open(path, flags, mode)
+}
+
+func Fallocate(fd int, mode uint32, off int64, len int64) (err error) {
+	return syscall.EOPNOTSUPP
+}