From 652f11380e44b7c2083fa19d706f5cddf7fe0718 Mon Sep 17 00:00:00 2001
From: Ayush Ranjan <ayushranjan@google.com>
Date: Mon, 26 Oct 2020 16:13:04 -0700
Subject: [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
---
 pkg/sentry/fsimpl/sys/sys.go | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

(limited to 'pkg/sentry/fsimpl/sys')

diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index 54fa5eced..7d2147141 100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
@@ -18,6 +18,7 @@ package sys
 import (
 	"bytes"
 	"fmt"
+	"strconv"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
@@ -29,9 +30,12 @@ import (
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
-// Name is the default filesystem name.
-const Name = "sysfs"
-const defaultSysDirMode = linux.FileMode(0755)
+const (
+	// Name is the default filesystem name.
+	Name                     = "sysfs"
+	defaultSysDirMode        = linux.FileMode(0755)
+	defaultMaxCachedDentries = uint64(1000)
+)
 
 // FilesystemType implements vfs.FilesystemType.
 //
@@ -62,9 +66,21 @@ func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		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("sys.FilesystemType.GetFilesystem: invalid dentry cache limit: dentry_cache_limit=%s", str)
+			return nil, nil, syserror.EINVAL
+		}
+	}
+
 	fs := &filesystem{
 		devMinor: devMinor,
 	}
+	fs.MaxCachedDentries = maxCachedDentries
 	fs.VFSFilesystem().Init(vfsObj, &fsType, fs)
 
 	root := fs.newDir(ctx, creds, defaultSysDirMode, map[string]kernfs.Inode{
-- 
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