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// Copyright 2018 Google Inc.
//
// 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 gofer
import (
"fmt"
"gvisor.googlesource.com/gvisor/pkg/sentry/context"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
)
// cachePolicy is a 9p cache policy. It has methods that determine what to
// cache (if anything) for a given inode.
type cachePolicy int
const (
// Cache nothing.
cacheNone cachePolicy = iota
// Use virtual file system cache for everything.
cacheAll
// Use virtual file system cache for everything, but send writes to the
// fs agent immediately.
cacheAllWritethrough
// Use the (host) page cache for reads/writes, but don't cache anything
// else. This allows the sandbox filesystem to stay in sync with any
// changes to the remote filesystem.
//
// This policy should *only* be used with remote filesystems that
// donate their host FDs to the sandbox and thus use the host page
// cache, otherwise the dirent state will be inconsistent.
cacheRemoteRevalidating
)
// String returns the string name of the cache policy.
func (cp cachePolicy) String() string {
switch cp {
case cacheNone:
return "cacheNone"
case cacheAll:
return "cacheAll"
case cacheAllWritethrough:
return "cacheAllWritethrough"
case cacheRemoteRevalidating:
return "cacheRemoteRevalidating"
default:
return "unknown"
}
}
func parseCachePolicy(policy string) (cachePolicy, error) {
switch policy {
case "fscache":
return cacheAll, nil
case "none":
return cacheNone, nil
case "fscache_writethrough":
return cacheAllWritethrough, nil
case "remote_revalidating":
return cacheRemoteRevalidating, nil
}
return cacheNone, fmt.Errorf("unsupported cache mode: %s", policy)
}
// cacheUAtters determines whether unstable attributes should be cached for the
// given inode.
func (cp cachePolicy) cacheUAttrs(inode *fs.Inode) bool {
if !fs.IsFile(inode.StableAttr) && !fs.IsDir(inode.StableAttr) {
return false
}
return cp == cacheAll || cp == cacheAllWritethrough
}
// cacheReaddir determines whether readdir results should be cached.
func (cp cachePolicy) cacheReaddir() bool {
return cp == cacheAll || cp == cacheAllWritethrough
}
// usePageCache determines whether the page cache should be used for the given
// inode. If the remote filesystem donates host FDs to the sentry, then the
// host kernel's page cache will be used, otherwise we will use a
// sentry-internal page cache.
func (cp cachePolicy) usePageCache(inode *fs.Inode) bool {
// Do cached IO for regular files only. Some "character devices" expect
// no caching.
if !fs.IsFile(inode.StableAttr) {
return false
}
return cp == cacheAll || cp == cacheAllWritethrough || cp == cacheRemoteRevalidating
}
// writeThough indicates whether writes to the file should be synced to the
// gofer immediately.
func (cp cachePolicy) writeThrough(inode *fs.Inode) bool {
return cp == cacheNone || cp == cacheAllWritethrough
}
// revalidate revalidates the child Inode if the cache policy allows it.
//
// Depending on the cache policy, revalidate will walk from the parent to the
// child inode, and if any unstable attributes have changed, will update the
// cached attributes on the child inode. If the walk fails, or the returned
// inode id is different from the one being revalidated, then the entire Dirent
// must be reloaded.
func (cp cachePolicy) revalidate(ctx context.Context, name string, parent, child *fs.Inode) bool {
if cp == cacheAll || cp == cacheAllWritethrough {
return false
}
if cp == cacheNone {
return true
}
childIops, ok := child.InodeOperations.(*inodeOperations)
if !ok {
panic(fmt.Sprintf("revalidating inode operations of unknown type %T", child.InodeOperations))
}
parentIops, ok := parent.InodeOperations.(*inodeOperations)
if !ok {
panic(fmt.Sprintf("revalidating inode operations with parent of unknown type %T", parent.InodeOperations))
}
// Walk from parent to child again.
//
// TODO: If we have a directory FD in the parent
// inodeOperations, then we can use fstatat(2) to get the inode
// attributes instead of making this RPC.
qids, _, mask, attr, err := parentIops.fileState.file.walkGetAttr(ctx, []string{name})
if err != nil {
// Can't look up the name. Trigger reload.
return true
}
// If the Path has changed, then we are not looking at the file file.
// We must reload.
if qids[0].Path != childIops.fileState.key.Inode {
return true
}
// If we are not caching unstable attrs, then there is nothing to
// update on this inode.
if !cp.cacheUAttrs(child) {
return false
}
// Update the inode's cached unstable attrs.
s := childIops.session()
childIops.cachingInodeOps.UpdateUnstable(unstable(ctx, mask, attr, s.mounter, s.client))
return false
}
// keep indicates that dirents should be kept pinned in the dirent tree even if
// there are no application references on the file.
func (cp cachePolicy) keep(d *fs.Dirent) bool {
if cp == cacheNone {
return false
}
sattr := d.Inode.StableAttr
// NOTE: Only cache files, directories, and symlinks.
return fs.IsFile(sattr) || fs.IsDir(sattr) || fs.IsSymlink(sattr)
}
// cacheNegativeDirents indicates that negative dirents should be held in the
// dirent tree.
func (cp cachePolicy) cacheNegativeDirents() bool {
return cp == cacheAll || cp == cacheAllWritethrough
}
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