From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: UDF alternate anchor block detection Date: Thu, 6 Oct 2011 23:50:46 +0200 Message-ID: <20111006215046.GL31367@quack.suse.cz> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linkinjeon@gmail.com To: Ashish Sangwan Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hello, On Fri 30-09-11 11:02:34, Ashish Sangwan wrote: > While mounting UDF media, when the primary AVDP is not found at block 256, > UDF code tries to read-in the alternate AVDP. > In the function udf_find_anchor, udf_scan_anchors is called 3 times, where > each call to udf_scan_anchors read 12 blocks. > In case there is no alternate AVDP stored, a total of 36 blocks are read > before mount fails - causing time delay for Mount Failure. > > After first call to udf_scan_anchors and before the second call there is > varconv conversion, for the older drivers, which skips 7 blocks after every > 32 blocks. What are these older drivers? Do we still require this code? Frankly, I don't know what are these older drives. The code has been like this when I started maintaining it and I didn't want to introduce regressions so I kept the varconv code in. > After varconv conversion, why is there a third call to udf_scan_anchors? In > the 1st call and 3rd call to udf_scan_anchors, exactly same blocks are read, > so this 3rd call seems to be redundant. This is not true - the second call uses udf_variable_to_fixed(sbi->s_last_block) as the last block on the media while the third call uses sbi->s_last_block as the last block on the media (both these scans are performed with varconv enabled). Again I have not seen a drive / medium where this would be needed but I believe original author had some reason to put the code in. I agree that the anchor searching code is a pain but that's how the standard is defined... > I suggest this modified code for udf_find_anchor :- > lastblock = > udf_scan_anchors(sb,udf_variable_to_fixed(sbi->s_last_block),fileset); > if (lastblock) > goto out; > else { > /* VARCONV didn't help. Clear it. */ > UDF_CLEAR_FLAG(sb, UDF_FLAG_VARCONV); > return 0; > } > > Please give your opininon to these 2 above points. If the code change seems > relevant than I can make patch for it. Honza -- Jan Kara SUSE Labs, CR