[WIP] Partial bot skeleton, non-functional though

vendor/github.com/cockroachdb/pebble/vfs/disk_usage_linux.go

@@ -0,0 +1,44 @@
+// Copyright 2020 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+//go:build linux
+// +build linux
+
+package vfs
+
+import "golang.org/x/sys/unix"
+
+func (defaultFS) GetDiskUsage(path string) (DiskUsage, error) {
+	stat := unix.Statfs_t{}
+	if err := unix.Statfs(path, &stat); err != nil {
+		return DiskUsage{}, err
+	}
+
+	// We use stat.Frsize here rather than stat.Bsize because on
+	// Linux Bavail and Bfree are in Frsize units.
+	//
+	// On most filesystems Frsize and Bsize will be set to the
+	// same value, but on some filesystems bsize returns the
+	// "optimal transfer block size"[1] which may be different
+	// (typically larger) than the actual block size.
+	//
+	// This confusion is cleared up in the statvfs[2] libc function,
+	// but the statfs system call used above varies across
+	// platforms.
+	//
+	// Frsize is used by GNU coreutils and other libraries, so
+	// this also helps ensure that we get the same results as one
+	// would get if they ran `df` on the given path.
+	//
+	// [1] https://man7.org/linux/man-pages/man2/statfs.2.html
+	// [2] https://man7.org/linux/man-pages/man3/statvfs.3.html
+	freeBytes := uint64(stat.Frsize) * uint64(stat.Bfree)
+	availBytes := uint64(stat.Frsize) * uint64(stat.Bavail)
+	totalBytes := uint64(stat.Frsize) * uint64(stat.Blocks)
+	return DiskUsage{
+		AvailBytes: availBytes,
+		TotalBytes: totalBytes,
+		UsedBytes:  totalBytes - freeBytes,
+	}, nil
+}