Plumbing context.Context to DecRef() and Release().

context is passed to DecRef() and Release() which is
needed for SO_LINGER implementation.

PiperOrigin-RevId: 324672584

8 files changed, 51 insertions, 50 deletions

diff --git a/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go b/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go
index 89caee3df..8f7d5a9bb 100644
--- a/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go
+++ b/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go
@@ -53,7 +53,7 @@ func setUp(b *testing.B, imagePath string) (context.Context, *vfs.VirtualFilesys
 
 	// Create VFS.
 	vfsObj := &vfs.VirtualFilesystem{}
-	if err := vfsObj.Init(); err != nil {
+	if err := vfsObj.Init(ctx); err != nil {
 		return nil, nil, nil, nil, err
 	}
 	vfsObj.MustRegisterFilesystemType("extfs", ext.FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
@@ -68,7 +68,7 @@ func setUp(b *testing.B, imagePath string) (context.Context, *vfs.VirtualFilesys
 	root := mntns.Root()
 
 	tearDown := func() {
-		root.DecRef()
+		root.DecRef(ctx)
 
 		if err := f.Close(); err != nil {
 			b.Fatalf("tearDown failed: %v", err)
@@ -169,7 +169,7 @@ func BenchmarkVFS2ExtfsMountStat(b *testing.B) {
 			if err != nil {
 				b.Fatalf("failed to walk to mount point: %v", err)
 			}
-			defer mountPoint.DecRef()
+			defer mountPoint.DecRef(ctx)
 
 			// Create extfs submount.
 			mountTearDown := mount(b, fmt.Sprintf("/tmp/image-%d.ext4", depth), vfsfs, &pop)
diff --git a/pkg/sentry/fsimpl/ext/dentry.go b/pkg/sentry/fsimpl/ext/dentry.go
index 55902322a..7a1b4219f 100644
--- a/pkg/sentry/fsimpl/ext/dentry.go
+++ b/pkg/sentry/fsimpl/ext/dentry.go
@@ -15,6 +15,7 @@
 package ext
 
 import (
+	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 )
 
@@ -55,7 +56,7 @@ func (d *dentry) TryIncRef() bool {
 }
 
 // DecRef implements vfs.DentryImpl.DecRef.
-func (d *dentry) DecRef() {
+func (d *dentry) DecRef(ctx context.Context) {
 	// FIXME(b/134676337): filesystem.mu may not be locked as required by
 	// inode.decRef().
 	d.inode.decRef()
@@ -64,7 +65,7 @@ func (d *dentry) DecRef() {
 // InotifyWithParent implements vfs.DentryImpl.InotifyWithParent.
 //
 // TODO(b/134676337): Implement inotify.
-func (d *dentry) InotifyWithParent(events, cookie uint32, et vfs.EventType) {}
+func (d *dentry) InotifyWithParent(ctx context.Context, events, cookie uint32, et vfs.EventType) {}
 
 // Watches implements vfs.DentryImpl.Watches.
 //
@@ -76,4 +77,4 @@ func (d *dentry) Watches() *vfs.Watches {
 // OnZeroWatches implements vfs.Dentry.OnZeroWatches.
 //
 // TODO(b/134676337): Implement inotify.
-func (d *dentry) OnZeroWatches() {}
+func (d *dentry) OnZeroWatches(context.Context) {}
diff --git a/pkg/sentry/fsimpl/ext/directory.go b/pkg/sentry/fsimpl/ext/directory.go
index 357512c7e..0fc01668d 100644
--- a/pkg/sentry/fsimpl/ext/directory.go
+++ b/pkg/sentry/fsimpl/ext/directory.go
@@ -142,7 +142,7 @@ type directoryFD struct {
 var _ vfs.FileDescriptionImpl = (*directoryFD)(nil)
 
 // Release implements vfs.FileDescriptionImpl.Release.
-func (fd *directoryFD) Release() {
+func (fd *directoryFD) Release(ctx context.Context) {
 	if fd.iter == nil {
 		return
 	}
diff --git a/pkg/sentry/fsimpl/ext/ext.go b/pkg/sentry/fsimpl/ext/ext.go
index dac6effbf..08ffc2834 100644
--- a/pkg/sentry/fsimpl/ext/ext.go
+++ b/pkg/sentry/fsimpl/ext/ext.go
@@ -123,32 +123,32 @@ func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 	fs.vfsfs.Init(vfsObj, &fsType, &fs)
 	fs.sb, err = readSuperBlock(dev)
 	if err != nil {
-		fs.vfsfs.DecRef()
+		fs.vfsfs.DecRef(ctx)
 		return nil, nil, err
 	}
 
 	if fs.sb.Magic() != linux.EXT_SUPER_MAGIC {
 		// mount(2) specifies that EINVAL should be returned if the superblock is
 		// invalid.
-		fs.vfsfs.DecRef()
+		fs.vfsfs.DecRef(ctx)
 		return nil, nil, syserror.EINVAL
 	}
 
 	// Refuse to mount if the filesystem is incompatible.
 	if !isCompatible(fs.sb) {
-		fs.vfsfs.DecRef()
+		fs.vfsfs.DecRef(ctx)
 		return nil, nil, syserror.EINVAL
 	}
 
 	fs.bgs, err = readBlockGroups(dev, fs.sb)
 	if err != nil {
-		fs.vfsfs.DecRef()
+		fs.vfsfs.DecRef(ctx)
 		return nil, nil, err
 	}
 
 	rootInode, err := fs.getOrCreateInodeLocked(disklayout.RootDirInode)
 	if err != nil {
-		fs.vfsfs.DecRef()
+		fs.vfsfs.DecRef(ctx)
 		return nil, nil, err
 	}
 	rootInode.incRef()
diff --git a/pkg/sentry/fsimpl/ext/ext_test.go b/pkg/sentry/fsimpl/ext/ext_test.go
index 64e9a579f..2dbaee287 100644
--- a/pkg/sentry/fsimpl/ext/ext_test.go
+++ b/pkg/sentry/fsimpl/ext/ext_test.go
@@ -65,7 +65,7 @@ func setUp(t *testing.T, imagePath string) (context.Context, *vfs.VirtualFilesys
 
 	// Create VFS.
 	vfsObj := &vfs.VirtualFilesystem{}
-	if err := vfsObj.Init(); err != nil {
+	if err := vfsObj.Init(ctx); err != nil {
 		t.Fatalf("VFS init: %v", err)
 	}
 	vfsObj.MustRegisterFilesystemType("extfs", FilesystemType{}, &vfs.RegisterFilesystemTypeOptions{
@@ -80,7 +80,7 @@ func setUp(t *testing.T, imagePath string) (context.Context, *vfs.VirtualFilesys
 	root := mntns.Root()
 
 	tearDown := func() {
-		root.DecRef()
+		root.DecRef(ctx)
 
 		if err := f.Close(); err != nil {
 			t.Fatalf("tearDown failed: %v", err)
diff --git a/pkg/sentry/fsimpl/ext/filesystem.go b/pkg/sentry/fsimpl/ext/filesystem.go
index 557963e03..c714ddf73 100644
--- a/pkg/sentry/fsimpl/ext/filesystem.go
+++ b/pkg/sentry/fsimpl/ext/filesystem.go
@@ -84,7 +84,7 @@ var _ vfs.FilesystemImpl = (*filesystem)(nil)
 //     - filesystem.mu must be locked (for writing if write param is true).
 //     - !rp.Done().
 //     - inode == vfsd.Impl().(*Dentry).inode.
-func stepLocked(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, inode *inode, write bool) (*vfs.Dentry, *inode, error) {
+func stepLocked(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, inode *inode, write bool) (*vfs.Dentry, *inode, error) {
 	if !inode.isDir() {
 		return nil, nil, syserror.ENOTDIR
 	}
@@ -100,7 +100,7 @@ func stepLocked(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, inode *inode, write boo
 		}
 		d := vfsd.Impl().(*dentry)
 		if name == ".." {
-			isRoot, err := rp.CheckRoot(vfsd)
+			isRoot, err := rp.CheckRoot(ctx, vfsd)
 			if err != nil {
 				return nil, nil, err
 			}
@@ -108,7 +108,7 @@ func stepLocked(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, inode *inode, write boo
 				rp.Advance()
 				return vfsd, inode, nil
 			}
-			if err := rp.CheckMount(&d.parent.vfsd); err != nil {
+			if err := rp.CheckMount(ctx, &d.parent.vfsd); err != nil {
 				return nil, nil, err
 			}
 			rp.Advance()
@@ -143,7 +143,7 @@ func stepLocked(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, inode *inode, write boo
 			child.name = name
 			dir.childCache[name] = child
 		}
-		if err := rp.CheckMount(&child.vfsd); err != nil {
+		if err := rp.CheckMount(ctx, &child.vfsd); err != nil {
 			return nil, nil, err
 		}
 		if child.inode.isSymlink() && rp.ShouldFollowSymlink() {
@@ -167,12 +167,12 @@ func stepLocked(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, inode *inode, write boo
 //
 // Preconditions:
 //     - filesystem.mu must be locked (for writing if write param is true).
-func walkLocked(rp *vfs.ResolvingPath, write bool) (*vfs.Dentry, *inode, error) {
+func walkLocked(ctx context.Context, rp *vfs.ResolvingPath, write bool) (*vfs.Dentry, *inode, error) {
 	vfsd := rp.Start()
 	inode := vfsd.Impl().(*dentry).inode
 	for !rp.Done() {
 		var err error
-		vfsd, inode, err = stepLocked(rp, vfsd, inode, write)
+		vfsd, inode, err = stepLocked(ctx, rp, vfsd, inode, write)
 		if err != nil {
 			return nil, nil, err
 		}
@@ -196,12 +196,12 @@ func walkLocked(rp *vfs.ResolvingPath, write bool) (*vfs.Dentry, *inode, error)
 // Preconditions:
 //     - filesystem.mu must be locked (for writing if write param is true).
 //     - !rp.Done().
-func walkParentLocked(rp *vfs.ResolvingPath, write bool) (*vfs.Dentry, *inode, error) {
+func walkParentLocked(ctx context.Context, rp *vfs.ResolvingPath, write bool) (*vfs.Dentry, *inode, error) {
 	vfsd := rp.Start()
 	inode := vfsd.Impl().(*dentry).inode
 	for !rp.Final() {
 		var err error
-		vfsd, inode, err = stepLocked(rp, vfsd, inode, write)
+		vfsd, inode, err = stepLocked(ctx, rp, vfsd, inode, write)
 		if err != nil {
 			return nil, nil, err
 		}
@@ -216,7 +216,7 @@ func walkParentLocked(rp *vfs.ResolvingPath, write bool) (*vfs.Dentry, *inode, e
 // the rp till the parent of the last component which should be an existing
 // directory. If parent is false then resolves rp entirely. Attemps to resolve
 // the path as far as it can with a read lock and upgrades the lock if needed.
-func (fs *filesystem) walk(rp *vfs.ResolvingPath, parent bool) (*vfs.Dentry, *inode, error) {
+func (fs *filesystem) walk(ctx context.Context, rp *vfs.ResolvingPath, parent bool) (*vfs.Dentry, *inode, error) {
 	var (
 		vfsd  *vfs.Dentry
 		inode *inode
@@ -227,9 +227,9 @@ func (fs *filesystem) walk(rp *vfs.ResolvingPath, parent bool) (*vfs.Dentry, *in
 	// of disk. This reduces congestion (allows concurrent walks).
 	fs.mu.RLock()
 	if parent {
-		vfsd, inode, err = walkParentLocked(rp, false)
+		vfsd, inode, err = walkParentLocked(ctx, rp, false)
 	} else {
-		vfsd, inode, err = walkLocked(rp, false)
+		vfsd, inode, err = walkLocked(ctx, rp, false)
 	}
 	fs.mu.RUnlock()
 
@@ -238,9 +238,9 @@ func (fs *filesystem) walk(rp *vfs.ResolvingPath, parent bool) (*vfs.Dentry, *in
 		// walk is fine as this is a read only filesystem.
 		fs.mu.Lock()
 		if parent {
-			vfsd, inode, err = walkParentLocked(rp, true)
+			vfsd, inode, err = walkParentLocked(ctx, rp, true)
 		} else {
-			vfsd, inode, err = walkLocked(rp, true)
+			vfsd, inode, err = walkLocked(ctx, rp, true)
 		}
 		fs.mu.Unlock()
 	}
@@ -283,7 +283,7 @@ func (fs *filesystem) statTo(stat *linux.Statfs) {
 
 // AccessAt implements vfs.Filesystem.Impl.AccessAt.
 func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds *auth.Credentials, ats vfs.AccessTypes) error {
-	_, inode, err := fs.walk(rp, false)
+	_, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
@@ -292,7 +292,7 @@ func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds
 
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
 func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetDentryOptions) (*vfs.Dentry, error) {
-	vfsd, inode, err := fs.walk(rp, false)
+	vfsd, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return nil, err
 	}
@@ -312,7 +312,7 @@ func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, op
 
 // GetParentDentryAt implements vfs.FilesystemImpl.GetParentDentryAt.
 func (fs *filesystem) GetParentDentryAt(ctx context.Context, rp *vfs.ResolvingPath) (*vfs.Dentry, error) {
-	vfsd, inode, err := fs.walk(rp, true)
+	vfsd, inode, err := fs.walk(ctx, rp, true)
 	if err != nil {
 		return nil, err
 	}
@@ -322,7 +322,7 @@ func (fs *filesystem) GetParentDentryAt(ctx context.Context, rp *vfs.ResolvingPa
 
 // OpenAt implements vfs.FilesystemImpl.OpenAt.
 func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	vfsd, inode, err := fs.walk(rp, false)
+	vfsd, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return nil, err
 	}
@@ -336,7 +336,7 @@ func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 
 // ReadlinkAt implements vfs.FilesystemImpl.ReadlinkAt.
 func (fs *filesystem) ReadlinkAt(ctx context.Context, rp *vfs.ResolvingPath) (string, error) {
-	_, inode, err := fs.walk(rp, false)
+	_, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return "", err
 	}
@@ -349,7 +349,7 @@ func (fs *filesystem) ReadlinkAt(ctx context.Context, rp *vfs.ResolvingPath) (st
 
 // StatAt implements vfs.FilesystemImpl.StatAt.
 func (fs *filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.StatOptions) (linux.Statx, error) {
-	_, inode, err := fs.walk(rp, false)
+	_, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return linux.Statx{}, err
 	}
@@ -360,7 +360,7 @@ func (fs *filesystem) StatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 
 // StatFSAt implements vfs.FilesystemImpl.StatFSAt.
 func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linux.Statfs, error) {
-	if _, _, err := fs.walk(rp, false); err != nil {
+	if _, _, err := fs.walk(ctx, rp, false); err != nil {
 		return linux.Statfs{}, err
 	}
 
@@ -370,7 +370,7 @@ func (fs *filesystem) StatFSAt(ctx context.Context, rp *vfs.ResolvingPath) (linu
 }
 
 // Release implements vfs.FilesystemImpl.Release.
-func (fs *filesystem) Release() {
+func (fs *filesystem) Release(ctx context.Context) {
 	fs.vfsfs.VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
 }
 
@@ -390,7 +390,7 @@ func (fs *filesystem) LinkAt(ctx context.Context, rp *vfs.ResolvingPath, vd vfs.
 		return syserror.EEXIST
 	}
 
-	if _, _, err := fs.walk(rp, true); err != nil {
+	if _, _, err := fs.walk(ctx, rp, true); err != nil {
 		return err
 	}
 
@@ -403,7 +403,7 @@ func (fs *filesystem) MkdirAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
 		return syserror.EEXIST
 	}
 
-	if _, _, err := fs.walk(rp, true); err != nil {
+	if _, _, err := fs.walk(ctx, rp, true); err != nil {
 		return err
 	}
 
@@ -416,7 +416,7 @@ func (fs *filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
 		return syserror.EEXIST
 	}
 
-	_, _, err := fs.walk(rp, true)
+	_, _, err := fs.walk(ctx, rp, true)
 	if err != nil {
 		return err
 	}
@@ -430,7 +430,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 		return syserror.ENOENT
 	}
 
-	_, _, err := fs.walk(rp, false)
+	_, _, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
@@ -440,7 +440,7 @@ func (fs *filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 
 // RmdirAt implements vfs.FilesystemImpl.RmdirAt.
 func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error {
-	_, inode, err := fs.walk(rp, false)
+	_, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
@@ -454,7 +454,7 @@ func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
 
 // SetStatAt implements vfs.FilesystemImpl.SetStatAt.
 func (fs *filesystem) SetStatAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.SetStatOptions) error {
-	_, _, err := fs.walk(rp, false)
+	_, _, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
@@ -468,7 +468,7 @@ func (fs *filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, targ
 		return syserror.EEXIST
 	}
 
-	_, _, err := fs.walk(rp, true)
+	_, _, err := fs.walk(ctx, rp, true)
 	if err != nil {
 		return err
 	}
@@ -478,7 +478,7 @@ func (fs *filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, targ
 
 // UnlinkAt implements vfs.FilesystemImpl.UnlinkAt.
 func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error {
-	_, inode, err := fs.walk(rp, false)
+	_, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
@@ -492,7 +492,7 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 
 // BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
 func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.BoundEndpointOptions) (transport.BoundEndpoint, error) {
-	_, inode, err := fs.walk(rp, false)
+	_, inode, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return nil, err
 	}
@@ -506,7 +506,7 @@ func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath
 
 // ListxattrAt implements vfs.FilesystemImpl.ListxattrAt.
 func (fs *filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath, size uint64) ([]string, error) {
-	_, _, err := fs.walk(rp, false)
+	_, _, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return nil, err
 	}
@@ -515,7 +515,7 @@ func (fs *filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath, si
 
 // GetxattrAt implements vfs.FilesystemImpl.GetxattrAt.
 func (fs *filesystem) GetxattrAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetxattrOptions) (string, error) {
-	_, _, err := fs.walk(rp, false)
+	_, _, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return "", err
 	}
@@ -524,7 +524,7 @@ func (fs *filesystem) GetxattrAt(ctx context.Context, rp *vfs.ResolvingPath, opt
 
 // SetxattrAt implements vfs.FilesystemImpl.SetxattrAt.
 func (fs *filesystem) SetxattrAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.SetxattrOptions) error {
-	_, _, err := fs.walk(rp, false)
+	_, _, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
@@ -533,7 +533,7 @@ func (fs *filesystem) SetxattrAt(ctx context.Context, rp *vfs.ResolvingPath, opt
 
 // RemovexattrAt implements vfs.FilesystemImpl.RemovexattrAt.
 func (fs *filesystem) RemovexattrAt(ctx context.Context, rp *vfs.ResolvingPath, name string) error {
-	_, _, err := fs.walk(rp, false)
+	_, _, err := fs.walk(ctx, rp, false)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/sentry/fsimpl/ext/regular_file.go b/pkg/sentry/fsimpl/ext/regular_file.go
index 66d14bb95..e73e740d6 100644
--- a/pkg/sentry/fsimpl/ext/regular_file.go
+++ b/pkg/sentry/fsimpl/ext/regular_file.go
@@ -79,7 +79,7 @@ type regularFileFD struct {
 }
 
 // Release implements vfs.FileDescriptionImpl.Release.
-func (fd *regularFileFD) Release() {}
+func (fd *regularFileFD) Release(context.Context) {}
 
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
diff --git a/pkg/sentry/fsimpl/ext/symlink.go b/pkg/sentry/fsimpl/ext/symlink.go
index 62efd4095..2fd0d1fa8 100644
--- a/pkg/sentry/fsimpl/ext/symlink.go
+++ b/pkg/sentry/fsimpl/ext/symlink.go
@@ -73,7 +73,7 @@ type symlinkFD struct {
 var _ vfs.FileDescriptionImpl = (*symlinkFD)(nil)
 
 // Release implements vfs.FileDescriptionImpl.Release.
-func (fd *symlinkFD) Release() {}
+func (fd *symlinkFD) Release(context.Context) {}
 
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *symlinkFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {