Introduce fsquota package
This introduces a new fsquota package and
a few low-level support packages to simplify the
management of filesystem quotas.
To expose an API that's nice to use while staying
performant and safe the new fsinfo syscall is being
used. Since that syscall is not yet in mainline it has
been backported to our 5.6 kernel.
Test Plan:
Manually validated on our kernel, automated
tests are pending some Bazel work to be able to run them
inside our own kernel.
X-Origin-Diff: phab/D462
GitOrigin-RevId: bb463056589d2b13b7cf32d48ab0b884e70b1bad
diff --git a/core/pkg/fsquota/fsinfo.go b/core/pkg/fsquota/fsinfo.go
new file mode 100644
index 0000000..e40a533
--- /dev/null
+++ b/core/pkg/fsquota/fsinfo.go
@@ -0,0 +1,59 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fsquota
+
+import (
+ "fmt"
+ "os"
+ "unsafe"
+
+ "golang.org/x/sys/unix"
+)
+
+// This requires fsinfo() support, which is not yet in any stable kernel.
+// Our kernel has that syscall backported. This would otherwise be an extremely expensive
+// operation and also involve lots of logic from our side.
+
+// From syscall_64.tbl
+const sys_fsinfo = 441
+
+// From uapi/linux/fsinfo.h
+const fsinfo_attr_source = 0x09
+const fsinfo_flags_query_path = 0x0000
+const fsinfo_flags_query_fd = 0x0001
+
+type fsinfoParams struct {
+ resolveFlags uint64
+ atFlags uint32
+ flags uint32
+ request uint32
+ nth uint32
+ mth uint32
+}
+
+func fsinfoGetSource(dir *os.File) (string, error) {
+ buf := make([]byte, 256)
+ params := fsinfoParams{
+ flags: fsinfo_flags_query_fd,
+ request: fsinfo_attr_source,
+ }
+ n, _, err := unix.Syscall6(sys_fsinfo, dir.Fd(), 0, uintptr(unsafe.Pointer(¶ms)), unsafe.Sizeof(params), uintptr(unsafe.Pointer(&buf[0])), 128)
+ if err != unix.Errno(0) {
+ return "", fmt.Errorf("failed to call fsinfo: %w", err)
+ }
+ return string(buf[:n]), nil
+}