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nilfs2: make superblock data array index computation sparse friendly

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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: e339ad31f5 ("nilfs2: introduce secondary super block")
Signed-off-by: Ryusuke 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ryusuke Konishi 2024-04-30 17:00:19 +09:00 committed by Andrew Morton
parent bbf45b7e68
commit 91d743a9c8
1 changed files with 18 additions and 2 deletions
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20
fs/nilfs2/the_nilfs.c
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@ -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;
}