[vfs] kernfs: Implement LRU cache for kernfs dentries.

Much like the VFS2 gofer client, kernfs too now caches dentries. The size of the
LRU cache is configurable via mount options.
Have adopted the same reference semantics from gofer client dentry.

Only sysfs and procfs use this LRU cache. The rest of the kernfs users (devpts,
fusefs, host, pipefs, sockfs) still use the no cache approach.

PiperOrigin-RevId: 339139835

1 files changed, 20 insertions, 2 deletions

diff --git a/pkg/sentry/fsimpl/proc/filesystem.go b/pkg/sentry/fsimpl/proc/filesystem.go
index ba809b92d..99abcab66 100644
--- a/pkg/sentry/fsimpl/proc/filesystem.go
+++ b/pkg/sentry/fsimpl/proc/filesystem.go
@@ -17,6 +17,7 @@ package proc
 
 import (
 	"fmt"
+	"strconv"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
@@ -24,10 +25,14 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
 )
 
-// Name is the default filesystem name.
-const Name = "proc"
+const (
+	// Name is the default filesystem name.
+	Name                     = "proc"
+	defaultMaxCachedDentries = uint64(1000)
+)
 
 // FilesystemType is the factory class for procfs.
 //
@@ -63,9 +68,22 @@ func (ft FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualF
 	if err != nil {
 		return nil, nil, err
 	}
+
+	mopts := vfs.GenericParseMountOptions(opts.Data)
+	maxCachedDentries := defaultMaxCachedDentries
+	if str, ok := mopts["dentry_cache_limit"]; ok {
+		delete(mopts, "dentry_cache_limit")
+		maxCachedDentries, err = strconv.ParseUint(str, 10, 64)
+		if err != nil {
+			ctx.Warningf("proc.FilesystemType.GetFilesystem: invalid dentry cache limit: dentry_cache_limit=%s", str)
+			return nil, nil, syserror.EINVAL
+		}
+	}
+
 	procfs := &filesystem{
 		devMinor: devMinor,
 	}
+	procfs.MaxCachedDentries = maxCachedDentries
 	procfs.VFSFilesystem().Init(vfsObj, &ft, procfs)
 
 	var cgroups map[string]string