184 lines
5.7 KiB
Go
184 lines
5.7 KiB
Go
// Copyright 2018 The gVisor Authors.
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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.dev/gvisor/pkg/sentry/context"
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"gvisor.dev/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 the (host) page cache for reads/writes, but don't cache anything
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// else. This allows the sandbox filesystem to stay in sync with any
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// changes to the remote filesystem.
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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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// useCachingInodeOps determines whether the page cache should be used for the
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// given inode. If the remote filesystem donates host FDs to the sentry, then
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// the 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) useCachingInodeOps(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
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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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// revalidate revalidates the child Inode if the cache policy allows it.
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//
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// Depending on the cache policy, revalidate will walk from the parent to the
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// child inode, and if any unstable attributes have changed, will update the
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// cached attributes on the child inode. If the walk fails, or the returned
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// inode id is different from the one being revalidated, then the entire Dirent
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// must be reloaded.
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func (cp cachePolicy) revalidate(ctx context.Context, name string, parent, child *fs.Inode) bool {
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if cp == cacheAll || cp == cacheAllWritethrough {
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return false
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}
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if cp == cacheNone {
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return true
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}
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childIops, ok := child.InodeOperations.(*inodeOperations)
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if !ok {
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panic(fmt.Sprintf("revalidating inode operations of unknown type %T", child.InodeOperations))
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}
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parentIops, ok := parent.InodeOperations.(*inodeOperations)
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if !ok {
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panic(fmt.Sprintf("revalidating inode operations with parent of unknown type %T", parent.InodeOperations))
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}
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// Walk from parent to child again.
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//
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// TODO(b/112031682): If we have a directory FD in the parent
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// inodeOperations, then we can use fstatat(2) to get the inode
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// attributes instead of making this RPC.
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qids, f, mask, attr, err := parentIops.fileState.file.walkGetAttr(ctx, []string{name})
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if err != nil {
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// Can't look up the name. Trigger reload.
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return true
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}
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f.close(ctx)
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// If the Path has changed, then we are not looking at the file file.
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// We must reload.
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if qids[0].Path != childIops.fileState.key.Inode {
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return true
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}
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// If we are not caching unstable attrs, then there is nothing to
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// update on this inode.
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if !cp.cacheUAttrs(child) {
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return false
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}
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// Update the inode's cached unstable attrs.
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s := childIops.session()
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childIops.cachingInodeOps.UpdateUnstable(unstable(ctx, mask, attr, s.mounter, s.client))
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return false
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}
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// keep indicates that dirents should be kept pinned in the dirent tree even if
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// there are no application references on the file.
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func (cp cachePolicy) keep(d *fs.Dirent) bool {
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if cp == cacheNone {
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return false
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}
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sattr := d.Inode.StableAttr
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// NOTE(b/31979197): 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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