Add a new cache policy FSCACHE_WRITETHROUGH.

The new policy is identical to FSCACHE (which caches everything in memory), but
it also flushes writes to the backing fs agent immediately.

All gofer cache policy decisions have been moved into the cachePolicy type.
Previously they were sprinkled around the codebase.

There are many different things that we cache (page cache, negative dirents,
dirent LRU, unstable attrs, readdir results....), and I don't think we should
have individual flags to control each of these.  Instead, we should have a few
high-level cache policies that are consistent and useful to users.  This
refactoring makes it easy to add more such policies.

PiperOrigin-RevId: 201206937
Change-Id: I6e225c382b2e5e1b0ad4ccf8ca229873f4cd389d

1 files changed, 10 insertions, 18 deletions

diff --git a/pkg/sentry/fs/gofer/inode.go b/pkg/sentry/fs/gofer/inode.go
index c00da5fec..fa9013b75 100644
--- a/pkg/sentry/fs/gofer/inode.go
+++ b/pkg/sentry/fs/gofer/inode.go
@@ -335,23 +335,15 @@ func (i *inodeOperations) Release(ctx context.Context) {
 
 // Mappable implements fs.InodeOperations.Mappable.
 func (i *inodeOperations) Mappable(inode *fs.Inode) memmap.Mappable {
-	if i.session().cachePolicy == cacheNone || !fs.IsFile(inode.StableAttr) {
-		return nil
+	if i.session().cachePolicy.usePageCache(inode) {
+		return i.cachingInodeOps
 	}
-	return i.cachingInodeOps
-}
-
-func isCachable(session *session, inode *fs.Inode) bool {
-	return session.cachePolicy != cacheNone && (fs.IsFile(inode.StableAttr) || fs.IsDir(inode.StableAttr))
-}
-
-func isFileCachable(session *session, inode *fs.Inode) bool {
-	return session.cachePolicy != cacheNone && fs.IsFile(inode.StableAttr)
+	return nil
 }
 
 // UnstableAttr implements fs.InodeOperations.UnstableAttr.
 func (i *inodeOperations) UnstableAttr(ctx context.Context, inode *fs.Inode) (fs.UnstableAttr, error) {
-	if isCachable(i.session(), inode) {
+	if i.session().cachePolicy.cacheUAttrs(inode) {
 		return i.cachingInodeOps.UnstableAttr(ctx, inode)
 	}
 	return i.fileState.unstableAttr(ctx)
@@ -433,7 +425,7 @@ func (i *inodeOperations) NonBlockingOpen(ctx context.Context, p fs.PermMask) (*
 }
 
 func (i *inodeOperations) getFileDefault(ctx context.Context, d *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
-	if !isFileCachable(i.session(), d.Inode) {
+	if !i.session().cachePolicy.usePageCache(d.Inode) {
 		h, err := newHandles(ctx, i.fileState.file, flags)
 		if err != nil {
 			return nil, err
@@ -456,7 +448,7 @@ func (i *inodeOperations) getFileDefault(ctx context.Context, d *fs.Dirent, flag
 
 // SetPermissions implements fs.InodeOperations.SetPermissions.
 func (i *inodeOperations) SetPermissions(ctx context.Context, inode *fs.Inode, p fs.FilePermissions) bool {
-	if isCachable(i.session(), inode) {
+	if i.session().cachePolicy.cacheUAttrs(inode) {
 		return i.cachingInodeOps.SetPermissions(ctx, inode, p)
 	}
 
@@ -473,7 +465,7 @@ func (i *inodeOperations) SetOwner(ctx context.Context, inode *fs.Inode, owner f
 		return nil
 	}
 
-	if isCachable(i.session(), inode) {
+	if i.session().cachePolicy.cacheUAttrs(inode) {
 		return i.cachingInodeOps.SetOwner(ctx, inode, owner)
 	}
 
@@ -492,7 +484,7 @@ func (i *inodeOperations) SetOwner(ctx context.Context, inode *fs.Inode, owner f
 
 // SetTimestamps implements fs.InodeOperations.SetTimestamps.
 func (i *inodeOperations) SetTimestamps(ctx context.Context, inode *fs.Inode, ts fs.TimeSpec) error {
-	if isCachable(i.session(), inode) {
+	if i.session().cachePolicy.cacheUAttrs(inode) {
 		return i.cachingInodeOps.SetTimestamps(ctx, inode, ts)
 	}
 
@@ -502,7 +494,7 @@ func (i *inodeOperations) SetTimestamps(ctx context.Context, inode *fs.Inode, ts
 // Truncate implements fs.InodeOperations.Truncate.
 func (i *inodeOperations) Truncate(ctx context.Context, inode *fs.Inode, length int64) error {
 	// This can only be called for files anyway.
-	if isFileCachable(i.session(), inode) {
+	if i.session().cachePolicy.usePageCache(inode) {
 		return i.cachingInodeOps.Truncate(ctx, inode, length)
 	}
 
@@ -511,7 +503,7 @@ func (i *inodeOperations) Truncate(ctx context.Context, inode *fs.Inode, length
 
 // WriteOut implements fs.InodeOperations.WriteOut.
 func (i *inodeOperations) WriteOut(ctx context.Context, inode *fs.Inode) error {
-	if !isCachable(i.session(), inode) {
+	if !i.session().cachePolicy.cacheUAttrs(inode) {
 		return nil
 	}