Commit 5ef22361 authored by Eric Biggers's avatar Eric Biggers Committed by Mikulas Patocka
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dm-verity-fec: simplify computation of ileaved 



fec_read_bufs() just iterates over a sequence of message blocks with
step size region_blocks.  At each step, 'ileaved' is just the offset (in
bytes) to one of these blocks.  Compute it in the straightforward way,
eliminating fec_interleave().

In more detail, previously the code computed
'ileaved = (n / k) + (n % k) * (region_blocks * block_size)'
where n = rsb * k + i and 0 <= i < k.  Substituting 'n' gives:

    ileaved = ((rsb * k + i) / k) + ((rsb * k + i) % k) * region_blocks * block_size
            = rsb + (i * region_blocks * block_size)

The result is more efficient and easier to understand.

Signed-off-by: default avatarEric Biggers <ebiggers@kernel.org>
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
parent 8ef45923

drivers/md/dm-verity-fec.c

+1 −12
Original line number Diff line number Diff line
@@ -23,17 +23,6 @@ static inline unsigned int fec_max_nbufs(struct dm_verity *v) 
	return 1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS);

}



/*

 * Return an interleaved offset for a byte in RS block.

 */

static inline u64 fec_interleave(struct dm_verity *v, u64 offset)

{

	u32 mod;



	mod = do_div(offset, v->fec->rs_k);

	return offset + mod * (v->fec->region_blocks << v->data_dev_block_bits);

}



/* Loop over each allocated buffer. */

#define fec_for_each_buffer(io, __i) \

	for (__i = 0; __i < (io)->nbufs; __i++)
@@ -204,7 +193,7 @@ static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io, 
	 * interleave contents to available bufs

	 */

	for (i = 0; i < v->fec->rs_k; i++) {

		ileaved = fec_interleave(v, rsb * v->fec->rs_k + i);

		ileaved = rsb + i * (v->fec->region_blocks << v->data_dev_block_bits);



		/*

		 * target is the data block we want to correct, target_index is