lib/file: make pre-allocate detect disk full errors and return them

lib/file/preallocate.go

@@ -0,0 +1,6 @@
+package file
+
+import "errors"
+
+// ErrDiskFull is returned from PreAllocate when it detects disk full
+var ErrDiskFull = errors.New("preallocate: file too big for remaining disk space")

lib/file/preallocate_unix.go

@@ -42,10 +42,10 @@ again:
 		goto again
 
 	}
-	// FIXME could be doing something here
-	// if err == unix.ENOSPC {
-	// 	log.Printf("No space")
-	// }
+	// Wrap important errors
+	if err == unix.ENOSPC {
+		return ErrDiskFull
+	}
 	return err
 }
 

lib/file/preallocate_windows.go

@@ -76,6 +76,9 @@ func PreAllocate(size int64, out *os.File) error {
 		uintptr(19), // FileAllocationInformation
 	)
 	if e1 != nil && e1 != syscall.Errno(0) {
+		if e1 == syscall.Errno(windows.ERROR_DISK_FULL) || e1 == syscall.Errno(windows.ERROR_HANDLE_DISK_FULL) {
+			return ErrDiskFull
+		}
 		return errors.Wrap(e1, "preAllocate NtSetInformationFile failed")
 	}