Re: [Nbd] BUG: read-command with data size 0 does not return a response header

[Wouter Verhelst <w@...112...>]

On Mon, Mar 04, 2013 at 04:29:23PM +0100, folkert wrote:
> Hi,
> 
> NBD-server v3.2 has a problem: if a client does a read-request of 0
> bytes in length, then the nbd-server does not return a response header.
> This is not in line with a write request which always returns a response
> header.
> This patch solves that behaviour:

applied.

> diff -uNrBbd nbd-3.2.org/nbd-server.c nbd-3.2/nbd-server.c
> --- nbd-3.2.org/nbd-server.c	2012-07-03 22:54:53.000000000 +0200
> +++ nbd-3.2/nbd-server.c	2013-03-04 16:21:04.000000000 +0100
> @@ -1821,11 +1821,11 @@
>  
>  		case NBD_CMD_READ:
>  			DEBUG("exp->buf, ");
> -			memcpy(buf, &reply, sizeof(struct nbd_reply));
>  			if (client->transactionlogfd != -1)
>  				writeit(client->transactionlogfd, &reply, sizeof(reply));
> -			p = buf + sizeof(struct nbd_reply);
> -			writelen = currlen + sizeof(struct nbd_reply);
> +			writeit(client->net, &reply, sizeof(reply));
> +			p = buf;
> +			writelen = currlen;
>  			while(len > 0) {
>  				if (expread(request.from, p, currlen, client)) {
>  					DEBUG("Read failed: %m");
> 
> After applying this fix, I measured that nbd-server has a latency of
> 0.02ms which is quite nice!
> 
> 
> Folkert van Heusden
> 
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