first commit

httpdl/alloc_linux.go

@@ -0,0 +1,27 @@
+//go:build linux
+
+package httpdl
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// allocate reserves disk space for the output file according to the
+// --file-allocation mode: none does nothing (sparse), trunc sets the size,
+// prealloc/falloc reserve real blocks with fallocate (falling back to a plain
+// truncate if the filesystem does not support it).
+func allocate(f *os.File, mode string, size int64) error {
+	switch mode {
+	case "none":
+		return nil
+	case "trunc":
+		return f.Truncate(size)
+	default: // prealloc, falloc
+		if err := unix.Fallocate(int(f.Fd()), 0, 0, size); err != nil {
+			return f.Truncate(size)
+		}
+		return nil
+	}
+}