Make cacheRemoteRevalidating detect changes to file size

When file size changes outside the sandbox, page cache was not
refreshing file size which is required for cacheRemoteRevalidating.
In fact, cacheRemoteRevalidating should be skipping the cache
completely since it's not really benefiting from it. The cache is
cache is already bypassed for unstable attributes (see
cachePolicy.cacheUAttrs). And althought the cache is called to
map pages, they will always miss the cache and map directly from
the host.

Created a HostMappable struct that maps directly to the host and
use it for files with cacheRemoteRevalidating.

Closes #124

PiperOrigin-RevId: 230998440
Change-Id: Ic5f632eabe33b47241e05e98c95e9b2090ae08fc

1 files changed, 3 insertions, 6 deletions

diff --git a/pkg/sentry/fs/gofer/file.go b/pkg/sentry/fs/gofer/file.go
index 3578b07a0..2181ddc68 100644
--- a/pkg/sentry/fs/gofer/file.go
+++ b/pkg/sentry/fs/gofer/file.go
@@ -204,7 +204,7 @@ func (f *fileOperations) Write(ctx context.Context, file *fs.File, src usermem.I
 		return 0, syserror.EISDIR
 	}
 	cp := f.inodeOperations.session().cachePolicy
-	if cp.usePageCache(file.Dirent.Inode) {
+	if cp.useCachingInodeOps(file.Dirent.Inode) {
 		n, err := f.inodeOperations.cachingInodeOps.Write(ctx, src, offset)
 		if err != nil {
 			return n, err
@@ -225,7 +225,7 @@ func (f *fileOperations) Read(ctx context.Context, file *fs.File, dst usermem.IO
 		return 0, syserror.EISDIR
 	}
 
-	if f.inodeOperations.session().cachePolicy.usePageCache(file.Dirent.Inode) {
+	if f.inodeOperations.session().cachePolicy.useCachingInodeOps(file.Dirent.Inode) {
 		return f.inodeOperations.cachingInodeOps.Read(ctx, file, dst, offset)
 	}
 	return dst.CopyOutFrom(ctx, f.handles.readWriterAt(ctx, offset))
@@ -267,10 +267,7 @@ func (f *fileOperations) Flush(ctx context.Context, file *fs.File) error {
 
 // ConfigureMMap implements fs.FileOperations.ConfigureMMap.
 func (f *fileOperations) ConfigureMMap(ctx context.Context, file *fs.File, opts *memmap.MMapOpts) error {
-	if !f.inodeOperations.session().cachePolicy.usePageCache(file.Dirent.Inode) {
-		return syserror.ENODEV
-	}
-	return fsutil.GenericConfigureMMap(file, f.inodeOperations.cachingInodeOps, opts)
+	return f.inodeOperations.configureMMap(file, opts)
 }
 
 // Seek implements fs.FileOperations.Seek.