Re: [PATCH] [CIFS]: Add clamp_length support

[David Howells <dhowells@redhat.com>]

Rohith Surabattula <rohiths.msft@gmail.com> wrote:

> > Rohith Surabattula <rohiths.msft@gmail.com> wrote:
> >
> > > +     credits = kmalloc(sizeof(struct cifs_credits), GFP_KERNEL);
> > > ...
> > > +     subreq->subreq_priv = credits;
> >
> > Would it be better if I made it so that the netfs could specify the size of
> > the netfs_read_subrequest struct to be allocated, thereby allowing it to tag
> > extra data on the end?
>
> Do you mean the clamp handler in netfs should return the size of data
> to be allocated instead of allocating itself ?

No, I was thinking of putting a size_t in struct netfs_request_ops that
indicates how big the subrequest struct should be:

	struct netfs_request_ops {
		...
		size_t subrequest_size;
	};

and then:

	struct netfs_read_subrequest *netfs_alloc_subrequest(
		struct netfs_read_request *rreq)
	{
		struct netfs_read_subrequest *subreq;

		subreq = kzalloc(rreq->ops->subrequest_size, GFP_KERNEL);
		if (subreq) {
			INIT_LIST_HEAD(&subreq->rreq_link);
			refcount_set(&subreq->usage, 2);
			subreq->rreq = rreq;
			netfs_get_read_request(rreq);
			netfs_stat(&netfs_n_rh_sreq);
		}

		return subreq;
	}

This would allow you to do, for instance:

	struct cifs_subrequest {
		struct netfs_read_subrequest subreq;
		struct cifs_credits credits;
	};

then:

	const struct netfs_request_ops cifs_req_ops = {
		.subrequest_size	= sizeof(struct cifs_subrequest),
		.init_rreq		= cifs_init_rreq,
		.expand_readahead	= cifs_expand_readahead,
		.clamp_length		= cifs_clamp_length,
		.issue_op		= cifs_req_issue_op,
		.done			= cifs_rreq_done,
		.cleanup		= cifs_req_cleanup,
	};

and then:

	static bool cifs_clamp_length(struct netfs_read_subrequest *subreq)
	{
		struct cifs_subrequest *cifs_subreq =
			container_of(subreq, struct cifs_subrequest, subreq);
		struct cifs_sb_info *cifs_sb = CIFS_SB(subreq->rreq->inode->i_sb);
		struct TCP_Server_Info *server;
		struct cifsFileInfo *open_file = subreq->rreq->netfs_priv;
		struct cifs_credits *credits = &cifs_subreq->credits;
		unsigned int rsize;
		int rc;

		server = cifs_pick_channel(tlink_tcon(open_file->tlink)->ses);

		rc = server->ops->wait_mtu_credits(server, cifs_sb->ctx->rsize,
	                                                   &rsize, credits);
		if (rc)
			return false;

		subreq->len = rsize;
		return true;
	}

David