Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756260Ab1CVOg5 (ORCPT ); Tue, 22 Mar 2011 10:36:57 -0400 Received: from smtp.nokia.com ([147.243.1.47]:36860 "EHLO mgw-sa01.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752196Ab1CVOgy (ORCPT ); Tue, 22 Mar 2011 10:36:54 -0400 Message-ID: <4D88B490.9060606@nokia.com> Date: Tue, 22 Mar 2011 16:39:12 +0200 From: Roger Quadros User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.2.15) Gecko/20110303 Lightning/1.0b2 Thunderbird/3.1.9 MIME-Version: 1.0 To: ext Alan Stern CC: , , , Subject: Re: [PATCH v2 2/3] usb: gadget: file_storage: Make CD-ROM emulation work with Mac OS-X References: In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [172.21.23.108] X-OriginalArrivalTime: 22 Mar 2011 14:36:17.0755 (UTC) FILETIME=[81097AB0:01CBE89E] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1984 Lines: 58 On 03/22/2011 04:26 PM, ext Alan Stern wrote: > On Tue, 22 Mar 2011, Roger Quadros wrote: > >> I have a question here. >> >> The host can request us to send less or more than the actual TOC size, since it >> has no clue how big it is. >> e.g. Linux host requests us to send only 12 bytes even though our formatted TOC >> length is 20. In this case should we return fsg->data_size_from_cmnd instead of >> actual TOC length? > > No. Always return the actual TOC length. OK. > >> e.g. Mac requests us to send 65534 bytes but our RAW TOC length is 37. >> The file storage driver seems to be zero padding our data response. So we >> respond with 65534 bytes, 37 of TOC and remaining zero padded. >> >> Can we do something like this to avoid unnecessary zero padded transfers? >> >> ret = fsg_get_toc(curlun, msf, format, buf); >> if (ret< 0) { >> curlun->sense_data = SS_INVALID_FIELD_IN_CDB; >> return -EINVAL; >> } else if (ret> fsg->data_size_from_cmnd) { >> ret = fsg->data_size_from_cmnd; >> } else { >> fsg->residue = ret; >> } >> return ret; > > Not needed (and not correct). The code at the end of do_scsi_command() > already does this: > > reply = min((u32) reply, fsg->data_size_from_cmnd); > ... > fsg->residue -= reply; > Oh yes, this explains why to return the actual TOC length in do_read_toc(). However, if host asked for data more than the TOC length then residue will be greater than zero and this will result in zero padded transfers. Not a big issue but should we be fixing it? one way could be to set fsg->residue to actual TOC length. in do_read_toc(). -- regards, -roger -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/