You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: roprov.go
    path of file: ./repos/lotus/storage/sealer
    
    the code of the file until where you have to start completion: package sealer

import (
	"context"

	"golang.org/x/xerrors"

	"github.com/filecoin-project/lotus/storage/paths"
	"github.com/filecoin-project/lotus/storage/sealer/storiface"
)

type readonlyProvider struct {
	index paths.SectorIndex
	stor  *paths.Local
}

func (l *readonlyProvider) AcquireSector(ctx context.Context, id storiface.Sect
    
func (l *readonlyProvider) AcquireSector(ctx context.Context, id storiface.SectorRef, existing storiface.SectorFileType, allocate storiface.SectorFileType, sealing storiface.PathType) (storiface.SectorPaths, func(), error) {
	if allocate != storiface.FTNone {
		return storiface.SectorPaths{}, nil, xerrors.New("read-only storage")
	}

	ctx, cancel := context.WithCancel(ctx)

	// use TryLock to avoid blocking
	locked, err := l.index.StorageTryLock(ctx, id.ID, existing, storiface.FTNone)
	if err != nil {
		cancel()
		return storiface.SectorPaths{}, nil, xerrors.Errorf("acquiring sector lock: %w", err)
	}
	if !locked {
		cancel()
		return storiface.SectorPaths{}, nil, xerrors.Errorf("failed to acquire sector lock")
	}

	p, _, err := l.stor.AcquireSector(ctx, id, existing, allocate, sealing, storiface.AcquireMove)

	return p, cancel, err
}