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 <dan.j.williams@xxxxxxxxx> >> Cc: Hannes Reinecke <hare@xxxxxxx> >> Cc: Jens Axboe <axboe@xxxxxxxxx> >> Cc: NeilBrown <neilb@xxxxxxx> >> Cc: Richard Fan <richard.fan@xxxxxxxx> >> Cc: Vishal L Verma <vishal.l.verma@xxxxxxxxx> >> --- >> Changelog: >> v3: add tester Richard Fan <richard.fan@xxxxxxxx> >> 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@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
