Re: [PATCH 08/10] tools/xenstored: Extend restore code to handle multiple input buffer

From: Luca Fancellu <luca.fancellu@arm.com>
To: Julien Grall <julien@xen.org>
Cc: xen-devel@lists.xenproject.org, raphning@amazon.co.uk,
	doebel@amazon.de, Julien Grall <jgrall@amazon.com>,
	Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>,
	Juergen Gross <jgross@suse.com>
Subject: Re: [PATCH 08/10] tools/xenstored: Extend restore code to handle multiple input buffer
Date: Mon, 21 Jun 2021 10:21:30 +0100	[thread overview]
Message-ID: <F12B315C-8C0C-4EEE-A3DE-209C8F9EA04E@arm.com> (raw)
In-Reply-To: <20210616144324.31652-9-julien@xen.org>


> On 16 Jun 2021, at 15:43, Julien Grall <julien@xen.org> wrote:
> 
> From: Julien Grall <jgrall@amazon.com>
> 
> Currently, the restore code is considering the stream will contain at
> most one in-flight request per connection. In a follow-up changes, we
> will want to transfer multiple in-flight requests.
> 
> The function read_state_buffered() is now extended to restore multiple
> in-flight request. Complete requests will be queued as delayed
> requests, if there a partial request (only the last one can) then it
> will used as the current in-flight request.
> 
> Note that we want to bypass the quota check for delayed requests as
> the new Xenstore may have a lower limit.
> 
> Lastly, there is no need to change the specification as there was
> no restriction on the number of in-flight requests preserved.
> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>

Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>

> ---
> tools/xenstore/xenstored_core.c | 56 ++++++++++++++++++++++++++++-----
> 1 file changed, 48 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
> index a5084a5b173d..5b7ab7f74013 100644
> --- a/tools/xenstore/xenstored_core.c
> +++ b/tools/xenstore/xenstored_core.c
> @@ -1486,6 +1486,10 @@ static void process_message(struct connection *conn, struct buffered_data *in)
> 	enum xsd_sockmsg_type type = in->hdr.msg.type;
> 	int ret;
> 
> +	/* At least send_error() and send_reply() expects conn->in == in */
> +	assert(conn->in == in);
> +	trace_io(conn, in, 0);
> +
> 	if ((unsigned int)type >= XS_TYPE_COUNT || !wire_funcs[type].func) {
> 		eprintf("Client unknown operation %i", type);
> 		send_error(conn, ENOSYS);
> @@ -1515,6 +1519,23 @@ static void process_message(struct connection *conn, struct buffered_data *in)
> 	conn->transaction = NULL;
> }
> 
> +static bool process_delayed_message(struct delayed_request *req)
> +{
> +	struct connection *conn = req->data;
> +	struct buffered_data *saved_in = conn->in;
> +
> +	/*
> +	 * Part of process_message() expects conn->in to contains the
> +	 * processed response. So save the current conn->in and restore it
> +	 * afterwards.
> +	 */
> +	conn->in = req->in;
> +	process_message(req->data, req->in);
> +	conn->in = saved_in;
> +
> +	return true;
> +}
> +
> static void consider_message(struct connection *conn)
> {
> 	if (verbose)
> @@ -1582,7 +1603,6 @@ static void handle_input(struct connection *conn)
> 	if (in->used != in->hdr.msg.len)
> 		return;
> 
> -	trace_io(conn, in, 0);
> 	consider_message(conn);
> 	return;
> 
> @@ -2611,14 +2631,20 @@ void read_state_buffered_data(const void *ctx, struct connection *conn,
> 	unsigned int len;
> 	bool partial = sc->data_resp_len;
> 
> -	if (sc->data_in_len) {
> +	for (data = sc->data; data < sc->data + sc->data_in_len; data += len) {
> 		bdata = new_buffer(conn);
> 		if (!bdata)
> 			barf("error restoring read data");
> -		if (sc->data_in_len < sizeof(bdata->hdr)) {
> +
> +		/*
> +		 * We don't know yet if there is more than one message
> +		 * to process. So the len is the size of the leftover data.
> +		 */
> +		len = sc->data_in_len - (data - sc->data);
> +		if (len < sizeof(bdata->hdr)) {
> 			bdata->inhdr = true;
> -			memcpy(&bdata->hdr, sc->data, sc->data_in_len);
> -			bdata->used = sc->data_in_len;
> +			memcpy(&bdata->hdr, sc->data, len);
> +			bdata->used = len;
> 		} else {
> 			bdata->inhdr = false;
> 			memcpy(&bdata->hdr, sc->data, sizeof(bdata->hdr));
> @@ -2629,12 +2655,26 @@ void read_state_buffered_data(const void *ctx, struct connection *conn,
> 							bdata->hdr.msg.len);
> 			if (!bdata->buffer)
> 				barf("Error allocating in buffer");
> -			bdata->used = sc->data_in_len - sizeof(bdata->hdr);
> -			memcpy(bdata->buffer, sc->data + sizeof(bdata->hdr),
> +			bdata->used = min_t(unsigned int,
> +					    len - sizeof(bdata->hdr),
> +					    bdata->hdr.msg.len);
> +			memcpy(bdata->buffer, data + sizeof(bdata->hdr),
> 			       bdata->used);
> +			/* Update len to match the size of the message. */
> +			len = bdata->used + sizeof(bdata->hdr);
> 		}
> 
> -		conn->in = bdata;
> +		/*
> +		 * If the message is not complete, then it means this was
> +		 * the current processed message. All the other messages
> +		 * will be queued to be handled after restoring.
> +		 */
> +		if (bdata->inhdr || bdata->used != bdata->hdr.msg.len) {
> +			assert(conn->in == NULL);
> +			conn->in = bdata;
> +		} else if (delay_request(conn, bdata, process_delayed_message,
> +					 conn, true))
> +			barf("Unable to delay the request");
> 	}
> 
> 	for (data = sc->data + sc->data_in_len;
> -- 
> 2.17.1
> 
>