syscallcompat: move syscall wrapper to their own package

We will get more of them as OSX also lacks support for openat.

2 files changed, 49 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
new file mode 100644
index 0000000..d437170
--- /dev/null
+++ b/internal/syscallcompat/sys_darwin.go
@@ -0,0 +1,12 @@
+package syscallcompat
+
+// 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) {
+	//
+	// Sorry, fallocate is not available on OSX at all and
+	// fcntl F_PREALLOCATE is not accessible from Go.
+	//
+	// See https://github.com/rfjakob/gocryptfs/issues/18 if you want to help.
+	return nil
+}
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
new file mode 100644
index 0000000..9fe9da5
--- /dev/null
+++ b/internal/syscallcompat/sys_linux.go
@@ -0,0 +1,37 @@
+package syscallcompat
+
+import (
+	"sync"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+const FALLOC_FL_KEEP_SIZE = 0x01
+
+var preallocWarn sync.Once
+
+// 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) {
+	for {
+		err = syscall.Fallocate(fd, FALLOC_FL_KEEP_SIZE, off, len)
+		if err == syscall.EINTR {
+			// fallocate, like many syscalls, can return EINTR. This is not an
+			// error and just signifies that the operation was interrupted by a
+			// signal and we should try again.
+			continue
+		}
+		if err == syscall.EOPNOTSUPP {
+			// ZFS does not support fallocate which caused gocryptfs to abort
+			// every write operation: https://github.com/rfjakob/gocryptfs/issues/22
+			preallocWarn.Do(func() {
+				tlog.Warn.Printf("Warning: The underlying filesystem " +
+					"does not support fallocate(2). gocryptfs will continue working " +
+					"but is no longer resistant against out-of-space errors.\n")
+			})
+			return nil
+		}
+		return err
+	}
+}