On Thu, Sep 23, 2021 at 11:40:30AM +0200, Hannes Reinecke wrote: > 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. No, I rejected the seq_file api for sysfs files, as it encourages abuse like this, sorry. greg k-h
