I developing block layered device driver. So, I intercept WRITE request and encrypt data, and decrypt data in the end_bio() routine (during processing and READ request). So all works fine in single stream. But I getting buffers content corruption if have tried to performs I/O from two and more processes simultaneously. I have not any local storage for buffers.
Do I'm need to count a BIO merging in my driver?
Is the Linux I/O subsystem have some requirements related to the a number of concurrent I/O request?
Is there some tips and tricks related stack using or compilation?
This is under kernel 4.15.
At the time I use next constriction to run over disk sectors:
/* * A portion of the bio_copy_data() ... */ for (vcnt = 0, src_iter = src->bi_iter; ; vcnt++) { if ( !src_iter.bi_size) { if ( !(src = src->bi_next) ) break; src_iter = src->bi_iter; } src_bv = bio_iter_iovec(src, src_iter); src_p = bv_page = kmap_atomic(src_bv.bv_page); src_p += src_bv.bv_offset; nlbn = src_bv.bv_len512; for ( ; nlbn--; lbn++ , src_p += 512 ) { { /* Simulate a processing of data in the I/O buffer */ char *srcp = src_p, *dstp = src_p; int count = DUDRV$K_SECTORSZ; while ( count--) { *(dstp++) = ~ (*(srcp++)); } } } kunmap_atomic(bv_page); **bio_advance_iter**(src, &src_iter, src_bv.bv_len); } Is this correct ? Or I'm need to use something like **bio_for_each_segment(bvl, bio, iter) ** ?
1 Answers
Answers 1
Have you considered the use of vmap with global synchronization, instead?
The use of kmap_atomic has some restrictions:
Since the mapping is restricted to the CPU that issued it, it performs well, but the issuing task is therefore required to stay on that CPU until it has finished, lest some other task displace its mappings.
kmap_atomic() may also be used by interrupt contexts, since it is does not sleep and the caller may not sleep until after kunmap_atomic() is called.
Reference: https://www.kernel.org/doc/Documentation/vm/highmem.txt
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