Commit 91d743a9 authored by Ryusuke Konishi's avatar Ryusuke Konishi Committed by Andrew Morton
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nilfs2: make superblock data array index computation sparse friendly 

Upon running sparse, "warning: dubious: x & !y" is output at an array
index calculation within nilfs_load_super_block().

The calculation is not wrong, but to eliminate the sparse warning, replace
it with an equivalent calculation.

Also, add a comment to make it easier to understand what the unintuitive
array index calculation is doing and whether it's correct.

Link: https://lkml.kernel.org/r/20240430080019.4242-3-konishi.ryusuke@gmail.com


Fixes: e339ad31 ("nilfs2: introduce secondary super block")
Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: kernel test robot <lkp@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent bbf45b7e

fs/nilfs2/the_nilfs.c

+18 −2
Original line number Diff line number Diff line
@@ -592,7 +592,7 @@ static int nilfs_load_super_block(struct the_nilfs *nilfs, 
	struct nilfs_super_block **sbp = nilfs->ns_sbp;

	struct buffer_head **sbh = nilfs->ns_sbh;

	u64 sb2off, devsize = bdev_nr_bytes(nilfs->ns_bdev);

	int valid[2], swp = 0;

	int valid[2], swp = 0, older;



	if (devsize < NILFS_SEG_MIN_BLOCKS * NILFS_MIN_BLOCK_SIZE + 4096) {

		nilfs_err(sb, "device size too small");
@@ -648,9 +648,25 @@ static int nilfs_load_super_block(struct the_nilfs *nilfs, 
	if (swp)

		nilfs_swap_super_block(nilfs);



	/*

	 * Calculate the array index of the older superblock data.

	 * If one has been dropped, set index 0 pointing to the remaining one,

	 * otherwise set index 1 pointing to the old one (including if both

	 * are the same).

	 *

	 *  Divided case             valid[0]  valid[1]  swp  ->  older

	 *  -------------------------------------------------------------

	 *  Both SBs are invalid        0         0       N/A (Error)

	 *  SB1 is invalid              0         1       1         0

	 *  SB2 is invalid              1         0       0         0

	 *  SB2 is newer                1         1       1         0

	 *  SB2 is older or the same    1         1       0         1

	 */

	older = valid[1] ^ swp;



	nilfs->ns_sbwcount = 0;

	nilfs->ns_sbwtime = le64_to_cpu(sbp[0]->s_wtime);

	nilfs->ns_prot_seq = le64_to_cpu(sbp[valid[1] & !swp]->s_last_seq);

	nilfs->ns_prot_seq = le64_to_cpu(sbp[older]->s_last_seq);

	*sbpp = sbp[0];

	return 0;

}