From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B6BDB3FC8 for ; Thu, 23 Sep 2021 09:40:32 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 262DA22350; Thu, 23 Sep 2021 09:40:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1632390031; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tdrkbcJaQpQrn/IHpFzCloC4zCeYqpehfTVZ0y9y7nI=; b=qBSKyhMIBtgtRWHLLpJDhaoNwH4u+oB2PSxzsHER0pOc4q5wZw+k6iZri+p179O5dLioqW HwyQLvCbp2KGSbI1s2TMd5qWxeuOO93lRnMXr88/k45KFl1Dcu+S5BLas6IFddp7163qLk 9TFpVYNTdRse6meyWLSH4iT0A0hKVX0= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1632390031; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tdrkbcJaQpQrn/IHpFzCloC4zCeYqpehfTVZ0y9y7nI=; b=aZDce/tZEfKNoJsQXI6WrZNYLS9HtSRFb2Ci9DEHRZhTbHbKGfCo9OF0L/0tvHG1/boff6 GViBT5kbtk34PmAQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 0BC7A13DCE; Thu, 23 Sep 2021 09:40:31 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id qaNfAo9LTGEiRQAAMHmgww (envelope-from ); Thu, 23 Sep 2021 09:40:31 +0000 Subject: Re: Too large badblocks sysfs file (was: [PATCH v3 0/7] badblocks improvement for multiple bad block ranges) To: Coly Li , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-raid@vger.kernel.org, nvdimm@lists.linux.dev Cc: antlists@youngman.org.uk, Dan Williams , Jens Axboe , NeilBrown , Richard Fan , Vishal L Verma , Greg Kroah-Hartman , rafael@kernel.org References: <20210913163643.10233-1-colyli@suse.de> From: Hannes Reinecke Message-ID: <6bd61a93-6fb6-2bd5-c1a6-b782e87845a4@suse.de> Date: Thu, 23 Sep 2021 11:40:30 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 9/23/21 7:59 AM, Coly Li wrote: > Hi all the kernel gurus, and folks in mailing lists, > > This is a question about exporting 4KB+ text information via sysfs > interface. I need advice on how to handle the problem. > > Recently I work on the bad blocks API (block/badblocks.c) improvement, > there is a sysfs file to export the bad block ranges for me raid. E.g > for a md raid1 device, file >     /sys/block/md0/md/rd0/bad_blocks > may contain the following text content, >     64 32 >    128 8 > The above lines mean there are two bad block ranges, one starts at LBA > 64, length 32 sectors, another one starts at LBA 128 and length 8 > sectors. All the content is generated from the internal bad block > records with 512 elements. In my testing the worst case only 185 from > 512 records can be displayed via the sysfs file if the LBA string is > very long, e.g.the following content, >   17668164135030776 512 >   17668164135029776 512 >   17668164135028776 512 >   17668164135027776 512 >   ... ... > The bad block ranges stored in internal bad blocks array are correct, > but the output message is truncated. This is the problem I encountered. > > I don't see sysfs has seq_file support (correct me if I am wrong), and I > know it is improper to transfer 4KB+ text via sysfs interface, but the > code is here already for long time. > > There are 2 ideas to fix showing up in my brain, > 1) Do not fix the problem >     Normally it is rare that a storage media has 100+ bad block ranges, > maybe in real world all the existing bad blocks information won't exceed > the page size limitation of sysfs file. > 2) Add seq_file support to sysfs interface if there is no > > It is probably there is other better solution to fix. So I do want to > get hint/advice from you. > > Thanks in advance for any comment :-) > > Coly Li > > On 9/14/21 12:36 AM, Coly Li wrote: >> This is the second effort to improve badblocks code APIs to handle >> multiple ranges in bad block table. >> >> There are 2 changes from previous version, >> - Fixes 2 bugs in front_overwrite() which are detected by the user >>    space testing code. >> - Provide the user space testing code in last patch. >> >> There is NO in-memory or on-disk format change in the whole series, all >> existing API and data structures are consistent. This series just only >> improve the code algorithm to handle more corner cases, the interfaces >> are same and consistency to all existing callers (md raid and nvdimm >> drivers). >> >> The original motivation of the change is from the requirement from our >> customer, that current badblocks routines don't handle multiple ranges. >> For example if the bad block setting range covers multiple ranges from >> bad block table, only the first two bad block ranges merged and rested >> ranges are intact. The expected behavior should be all the covered >> ranges to be handled. >> >> All the patches are tested by modified user space code and the code >> logic works as expected. The modified user space testing code is >> provided in last patch. The testing code detects 2 defects in helper >> front_overwrite() and fixed in this version. >> >> The whole change is divided into 6 patches to make the code review more >> clear and easier. If people prefer, I'd like to post a single large >> patch finally after the code review accomplished. >> >> This version is seriously tested, and so far no more defect observed. >> >> >> Coly Li >> >> Cc: Dan Williams >> Cc: Hannes Reinecke >> Cc: Jens Axboe >> Cc: NeilBrown >> Cc: Richard Fan >> Cc: Vishal L Verma >> --- >> Changelog: >> v3: add tester Richard Fan >> v2: the improved version, and with testing code. >> v1: the first completed version. >> >> >> Coly Li (6): >>    badblocks: add more helper structure and routines in badblocks.h >>    badblocks: add helper routines for badblock ranges handling >>    badblocks: improvement badblocks_set() for multiple ranges handling >>    badblocks: improve badblocks_clear() for multiple ranges handling >>    badblocks: improve badblocks_check() for multiple ranges handling >>    badblocks: switch to the improved badblock handling code >> Coly Li (1): >>    test: user space code to test badblocks APIs >> >>   block/badblocks.c         | 1599 ++++++++++++++++++++++++++++++------- >>   include/linux/badblocks.h |   32 + >>   2 files changed, 1340 insertions(+), 291 deletions(-) >> > Please have a look at the patchset 'start switching sysfs attributes to expose the seq_file' from Christoph Hellwig on linux-block; that seems to be the approach you are looking for. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer