fallocate: copy implementation from beeper-imessage

Signed-off-by: Sumner Evans <[email protected]>

fallocate/doc.go

@@ -0,0 +1,9 @@
+// Copyright (C) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// Package fallocate provides a unified interface for preallocating space for a
+// file.
+package fallocate

fallocate/fallocate_darwin.go

@@ -0,0 +1,29 @@
+// Copyright (C) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+//go:build darwin
+
+package fallocate
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+var ErrOutOfSpace error = unix.ENOSPC
+
+func Fallocate(file *os.File, size int) error {
+	if size <= 0 {
+		return nil
+	}
+	return unix.FcntlFstore(uintptr(file.Fd()), unix.F_PREALLOCATE, &unix.Fstore_t{
+		Flags:   unix.F_ALLOCATEALL,
+		Posmode: unix.F_PEOFPOSMODE,
+		Offset:  0,
+		Length:  int64(size),
+	})
+}

fallocate/fallocate_linux.go

@@ -0,0 +1,24 @@
+// Copyright (C) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+//go:build linux
+
+package fallocate
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+var ErrOutOfSpace error = unix.ENOSPC
+
+func Fallocate(file *os.File, size int) error {
+	if size <= 0 {
+		return nil
+	}
+	return unix.Fallocate(int(file.Fd()), 0, 0, int64(size))
+}

fallocate/fallocate_unknown.go

@@ -0,0 +1,17 @@
+// Copyright (C) 2024 Sumner Evans
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+//go:build !linux && !android && !darwin
+
+package fallocate
+
+import "os"
+
+var ErrOutOfSpace error = nil
+
+func Fallocate(file *os.File, size int) error {
+	return nil
+}