On 09-09-2021 11:18, Christoph Hellwig wrote: > On Thu, Sep 09, 2021 at 11:06:53AM +0530, Praveen Kumar wrote: >> There are use-cases like replication where need to hook the blk I/O >> operations for devices and perform specific operation and fallback to >> its original I/O operations. >> Prior to v5.9 there was make_request_fn and then blk_mq_submit_bio >> exported apis, which provided infrastructure to drivers to develop these >> features. However in v5.10-rc1 with below commit the API was removed >> from the export list. >> >> Previous commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.10-rc1&id=681cc5e8667e8579a2da8fa4090c48a2d73fc3bb >> >> This patch exports the blk_mq_submit_bio symbol to provide flexibility >> to the drivers. > > Please send your users of this "feature" to this list for inclusion > and we'll help you to massage them into a non-broken version. > Thank you for the response and appreciate your help. Providing a bit of details below. The disk replication solution which I mentioned, hooks all the block i/o operation using make_request_fn for specific device request queue and do some massaging and then call the standard block operations. The flow is something like below : replication_func_init (struct block_device *bdev) ... orig_queue = bdev_get_queue(bdev) // save the original state ... orig_request_fn = orig_queue->request_fn; ... orig_queue->make_request_fn = custom_function(say "replicate_request_func") replicate_request_func(...) { ... does some driver specific massaging ... // calls original if (orig_queue->make_request_fn) orig_queue->make_request_fn(...) else blk_mq_make_request(...) ... Now, the current implementation have make_request_fn moved to submit_bio, one probable approach is to somehow, update the original submit_bio to custom "replicate_submit_bio_func" and then handle the case likewise as done in "replicate_request_func". But, "blk_mq_submit_bio" is not exported symbol.. Second, "submit_bio_noacct" is the next approach which we thought can be used for submit the bio, but, for case where original submit_bio is NULL, we will end calling recursively the new submit_bio, and panic. replicate_submit_bio_func ... does some driver specific massaging ... // calls exported symbol submit_bio_noacct __submit_bio_noacct(bio) __submit_bio disk->fops->submit_bio(bio) -> updated API replicate_submit_bio_func submit_bio_noacct Hope, the provided information helps understanding the problem. If not, please do let us know, we will try to provide more details accordingly. Also, please do provide your thoughts and suggestions how can we achieve the above kind of functionality on latest kernel version. Further, we were trying to understand the history over the removal of make_request_fn in the queue within blk_mq_init_allocated_queue API, but didn't find much. Can you please provide any information regarding the same. Also, is there a possibility of have similar kind of implemenation for submit_bio ? ... - q->make_request_fn = blk_mq_make_request; ... Patch : https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/block/blk-mq.c?h=v5.14&id=8cf7961dab42c9177a556b719c15f5b9449c24d1 Regards, ~Praveen.
