140 lines
4.3 KiB
Go
140 lines
4.3 KiB
Go
// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package gofer
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import (
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"fmt"
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"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
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)
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// cachePolicy is a 9p cache policy. It has methods that determine what to
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// cache (if anything) for a given inode.
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type cachePolicy int
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const (
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// Cache nothing.
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cacheNone cachePolicy = iota
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// Use virtual file system cache for everything.
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cacheAll
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// Use virtual file system cache for everything, but send writes to the
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// fs agent immediately.
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cacheAllWritethrough
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// Use virtual file system cache for everything, but reload dirents
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// from the remote filesystem on each lookup. Thus, if the remote
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// filesystem has changed, the returned dirent will have the updated
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// state.
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//
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// This policy should *only* be used with remote filesystems that
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// donate their host FDs to the sandbox and thus use the host page
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// cache, otherwise the dirent state will be inconsistent.
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cacheRemoteRevalidating
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)
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// String returns the string name of the cache policy.
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func (cp cachePolicy) String() string {
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switch cp {
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case cacheNone:
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return "cacheNone"
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case cacheAll:
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return "cacheAll"
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case cacheAllWritethrough:
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return "cacheAllWritethrough"
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case cacheRemoteRevalidating:
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return "cacheRemoteRevalidating"
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default:
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return "unknown"
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}
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}
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func parseCachePolicy(policy string) (cachePolicy, error) {
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switch policy {
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case "fscache":
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return cacheAll, nil
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case "none":
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return cacheNone, nil
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case "fscache_writethrough":
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return cacheAllWritethrough, nil
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case "remote_revalidating":
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return cacheRemoteRevalidating, nil
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}
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return cacheNone, fmt.Errorf("unsupported cache mode: %s", policy)
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}
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// cacheUAtters determines whether unstable attributes should be cached for the
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// given inode.
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func (cp cachePolicy) cacheUAttrs(inode *fs.Inode) bool {
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if !fs.IsFile(inode.StableAttr) && !fs.IsDir(inode.StableAttr) {
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return false
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}
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return cp == cacheAll || cp == cacheAllWritethrough
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}
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// cacheReaddir determines whether readdir results should be cached.
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func (cp cachePolicy) cacheReaddir() bool {
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return cp == cacheAll || cp == cacheAllWritethrough
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}
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// usePageCache determines whether the page cache should be used for the given
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// inode. If the remote filesystem donates host FDs to the sentry, then the
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// host kernel's page cache will be used, otherwise we will use a
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// sentry-internal page cache.
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func (cp cachePolicy) usePageCache(inode *fs.Inode) bool {
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// Do cached IO for regular files only. Some "character devices" expect
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// no caching.
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if !fs.IsFile(inode.StableAttr) {
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return false
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}
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return cp == cacheAll || cp == cacheAllWritethrough || cp == cacheRemoteRevalidating
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}
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// writeThough indicates whether writes to the file should be synced to the
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// gofer immediately.
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func (cp cachePolicy) writeThrough(inode *fs.Inode) bool {
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return cp == cacheNone || cp == cacheAllWritethrough
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}
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// revalidateDirent indicates that a dirent should be revalidated after a
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// lookup, because the looked up version may be stale.
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func (cp cachePolicy) revalidateDirent() bool {
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if cp == cacheAll || cp == cacheAllWritethrough {
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return false
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}
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// TODO: The cacheRemoteRevalidating policy should only
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// return true if the remote file's attributes have changed.
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return true
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}
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// keepDirent indicates that dirents should be kept pinned in the dirent tree
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// even if there are no application references on the file.
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func (cp cachePolicy) keepDirent(inode *fs.Inode) bool {
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if cp == cacheNone {
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return false
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}
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sattr := inode.StableAttr
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// NOTE: Only cache files, directories, and symlinks.
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return fs.IsFile(sattr) || fs.IsDir(sattr) || fs.IsSymlink(sattr)
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}
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// cacheNegativeDirents indicates that negative dirents should be held in the
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// dirent tree.
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func (cp cachePolicy) cacheNegativeDirents() bool {
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return cp == cacheAll || cp == cacheAllWritethrough
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}
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