[LU-16138] remove need for T10-PI block integrity patches from server kernel

Related — Mon, 2 Oct 2023 23:38:02 +0000

Kernels since v4.3-rc4-30-g0f8087ecdeac separate the block integrity verify and generate functions into a separate struct blk_integrity_profile instead of copying the pointers into struct blk_integrity. This might be used to facilitate replacing the blk_integrity_profile pointer on the block device for the duration that osd-ldiskfs is mounting it, and potentially avoid the need to patch the kernel for T10-PI at all.

As a starting point, we would need to call blk_integrity_register() using a template holding the integrity methods provided by osd-ldiskfs - osd_dif_type<1,3>generate<crc,ip>() and osd_dif_type<1,3>verify<crc,ip>(). It looks like this function is just copying the individual fields from the provided template into the disk queue's blk_integrity fields, so we should save the original blk_integrity to be restored when osdldiskfs unmounts the target, otherwise the kernel would crash trying to access the old function pointers if there is any block device IO after osd-ldiskfs is removed from the kernel.

It seems prudent to call blk_integrity_unregister() before unloading the module, as that would force all block device IO using the osd-ldiskfs.ko methods to be finished, and then blk_integrity_register() the saved values so that T10-PI is still functional on the device.

The osd_dif_generate() and osd_dif_verify() functions need to handle being called on block read/write calls that are unrelated to osd-ldiskfs BRW IOs, since that will now happen for every block in the filesystem whether or not it came from osd-ldiskfs. One way to separate OSD vs. non-OSD IO might be by putting a magic at the end of struct osd_bio_private that can be used to reliably detect if this is a BRW IO or if it is IO on some other ldiskfs block. Non-BRW blocks would return NULL from find_lnb() and not dereference bio_private if NULL, and it looks like the rest of the code will "just work".

Whamcloud Community JIRA

[LU-16138] remove need for T10-PI block integrity patches from server kernel