Implement cgroupfs.

A skeleton implementation of cgroupfs. It supports trivial cpu and
memory controllers with no support for hierarchies.

PiperOrigin-RevId: 366561126

2 files changed, 17 insertions, 3 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
index 65054b0ea..84b1c3745 100644
--- a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
@@ -25,8 +25,10 @@ import (
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
-// DynamicBytesFile implements kernfs.Inode and represents a read-only
-// file whose contents are backed by a vfs.DynamicBytesSource.
+// DynamicBytesFile implements kernfs.Inode and represents a read-only file
+// whose contents are backed by a vfs.DynamicBytesSource. If data additionally
+// implements vfs.WritableDynamicBytesSource, the file also supports dispatching
+// writes to the implementer, but note that this will not update the source data.
 //
 // Must be instantiated with NewDynamicBytesFile or initialized with Init
 // before first use.
@@ -40,7 +42,9 @@ type DynamicBytesFile struct {
 	InodeNotSymlink
 
 	locks vfs.FileLocks
-	data  vfs.DynamicBytesSource
+	// data can additionally implement vfs.WritableDynamicBytesSource to support
+	// writes.
+	data vfs.DynamicBytesSource
 }
 
 var _ Inode = (*DynamicBytesFile)(nil)
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index 565d723f0..16486eeae 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -61,6 +61,7 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/refsvfs2"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
@@ -508,6 +509,15 @@ func (d *Dentry) Inode() Inode {
 	return d.inode
 }
 
+// FSLocalPath returns an absolute path to d, relative to the root of its
+// filesystem.
+func (d *Dentry) FSLocalPath() string {
+	var b fspath.Builder
+	_ = genericPrependPath(vfs.VirtualDentry{}, nil, d, &b)
+	b.PrependByte('/')
+	return b.String()
+}
+
 // The Inode interface maps filesystem-level operations that operate on paths to
 // equivalent operations on specific filesystem nodes.
 //