From: "NeilBrown" <email@example.com> To: "Coly Li" <firstname.lastname@example.org> Cc: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, "Dan Williams" <firstname.lastname@example.org>, "Hannes Reinecke" <email@example.com>, "Jens Axboe" <firstname.lastname@example.org>, "Richard Fan" <email@example.com>, "Vishal L Verma" <firstname.lastname@example.org>, "Greg Kroah-Hartman" <email@example.com>, firstname.lastname@example.org Subject: Re: Too large badblocks sysfs file (was: [PATCH v3 0/7] badblocks improvement for multiple bad block ranges) Date: Thu, 23 Sep 2021 20:09:21 +1000 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> On Thu, 23 Sep 2021, 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. Why do you think there is a problem? As documented in Documentation/admin-guide/md.rst, the truncation at 1 page is expected and by design. The "unacknowledge-bad-blocks" file is the important one that is needed for correct behaviour. Being able to read a single block is sufficient, though being able to read more than one could provide better performance in some cases. The "bad-blocks" file primarily exist to provide visibility into the state of the system - useful during development. It can be written to to add bad blocks. I never *needs* to be read from. The authoritative source of information about the set of bad blocks is the on-disk data the can be and should be read directly... Except that mdadm does. That was a mistake. check_for_cleared_bb() is wrong. I wonder why it was added. The commit message doesn't give any justification. NeilBrown > > 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 <email@example.com> > > Cc: Hannes Reinecke <firstname.lastname@example.org> > > Cc: Jens Axboe <email@example.com> > > Cc: NeilBrown <firstname.lastname@example.org> > > Cc: Richard Fan <email@example.com> > > Cc: Vishal L Verma <firstname.lastname@example.org> > > --- > > Changelog: > > v3: add tester Richard Fan <email@example.com> > > 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(-) > > > >
next prev parent reply other threads:[~2021-09-23 10:09 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-13 16:36 [PATCH v3 0/7] badblocks improvement for multiple bad block ranges Coly Li 2021-09-13 16:36 ` [PATCH v3 1/6] badblocks: add more helper structure and routines in badblocks.h Coly Li 2021-09-27 7:23 ` Geliang Tang 2021-09-27 8:23 ` Coly Li 2021-09-13 16:36 ` [PATCH v3 2/6] badblocks: add helper routines for badblock ranges handling Coly Li 2021-09-27 7:25 ` Geliang Tang 2021-09-27 8:17 ` Coly Li 2021-09-13 16:36 ` [PATCH v3 3/6] badblocks: improvement badblocks_set() for multiple " Coly Li 2021-09-27 7:30 ` Geliang Tang 2021-09-27 8:16 ` Coly Li 2021-09-13 16:36 ` [PATCH v3 4/6] badblocks: improve badblocks_clear() " Coly Li 2021-09-13 16:36 ` [PATCH v3 5/6] badblocks: improve badblocks_check() " Coly Li 2021-09-13 16:36 ` [PATCH v3 6/6] badblocks: switch to the improved badblock handling code Coly Li 2021-09-13 16:36 ` [PATCH] test: user space code to test badblocks APIs Coly Li 2021-09-23 5:59 ` Too large badblocks sysfs file (was: [PATCH v3 0/7] badblocks improvement for multiple bad block ranges) Coly Li 2021-09-23 6:08 ` Greg Kroah-Hartman 2021-09-23 6:14 ` Coly Li 2021-09-23 6:47 ` Greg Kroah-Hartman 2021-09-23 7:13 ` Coly Li 2021-09-23 9:40 ` Hannes Reinecke 2021-09-23 9:57 ` Greg Kroah-Hartman 2021-09-23 10:09 ` NeilBrown [this message] 2021-09-23 10:39 ` Greg Kroah-Hartman 2021-09-23 12:55 ` Coly Li
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