From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:34353) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ra4gW-0007fI-Ne for qemu-devel@nongnu.org; Mon, 12 Dec 2011 07:08:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ra4gR-0004mH-4m for qemu-devel@nongnu.org; Mon, 12 Dec 2011 07:08:44 -0500 Received: from mail-lpp01m010-f45.google.com ([209.85.215.45]:54070) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ra4gQ-0004m0-Uu for qemu-devel@nongnu.org; Mon, 12 Dec 2011 07:08:39 -0500 Received: by lags15 with SMTP id s15so2199059lag.4 for ; Mon, 12 Dec 2011 04:08:38 -0800 (PST) Date: Mon, 12 Dec 2011 12:08:33 +0000 From: Stefan Hajnoczi Message-ID: <20111212120833.GA22654@stefanha-thinkpad.localdomain> References: <1323101930-27163-1-git-send-email-mohan@in.ibm.com> <1323101930-27163-5-git-send-email-mohan@in.ibm.com> <20111208183114.GC20998@stefanha-thinkpad.localdomain> <201112092212.20343.mohan@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201112092212.20343.mohan@in.ibm.com> Subject: Re: [Qemu-devel] [PATCH V4 04/13] hw/9pfs: File system helper process for qemu 9p proxy FS List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "M. Mohan Kumar" Cc: "M. Mohan Kumar" , qemu-devel@nongnu.org, aneesh.kumar@linux.vnet.ibm.com On Fri, Dec 09, 2011 at 10:12:17PM +0530, M. Mohan Kumar wrote: > On Friday, December 09, 2011 12:01:14 AM Stefan Hajnoczi wrote: > > On Mon, Dec 05, 2011 at 09:48:41PM +0530, M. Mohan Kumar wrote: > > > +static int read_request(int sockfd, struct iovec *iovec, ProxyHeader > > > *header) +{ > > > + int retval; > > > + > > > + /* > > > + * read the request header. > > > + */ > > > + iovec->iov_len = 0; > > > + retval = socket_read(sockfd, iovec->iov_base, PROXY_HDR_SZ); > > > + if (retval < 0) { > > > + return retval; > > > + } > > > + iovec->iov_len = PROXY_HDR_SZ; > > > + retval = proxy_unmarshal(iovec, 0, "dd", &header->type, > > > &header->size); + if (retval < 0) { > > > + return retval; > > > + } > > > + /* > > > + * We can't process message.size > PROXY_MAX_IO_SZ, read the > > > complete + * message from the socket and ignore it. This ensures > > > that + * we can correctly handle the next request. We also return + > > > * ENOBUFS as error to indicate we ran out of buffer space. + */ > > > + if (header->size > PROXY_MAX_IO_SZ) { > > > + int count, size; > > > + size = header->size; > > > + while (size > 0) { > > > + count = MIN(PROXY_MAX_IO_SZ, size); > > > + count = socket_read(sockfd, iovec->iov_base + PROXY_HDR_SZ, > > > count); + if (count < 0) { > > > + return count; > > > + } > > > + size -= count; > > > + } > > > > I'm not sure recovery attempts are worthwhile here. The client is > > buggy, perhaps just refuse further work. > > But whats the issue in trying to recover in this case? This recovery procedure is not robust because it does not always work. In fact it only works in the case where the header->size field was out-of-range but accurate. That's not a likely case since the QEMU-side code that you are writing should handle this. If the nature of the invalid request is different, either a broken or malicious client which does not send a valid header->size then we're stuck in this special-case recovery trying to gobble bytes and we never log an error. A real recovery would be something like disconnecting and re-establishing the connection between QEMU and the helper. This would allow us to get back to a clean state in all cases. Stefan