On Fri, Mar 24, 2017 at 12:13:35PM -0700, Liu Bo wrote:
> Now that scrub can fix data errors with the help of parity for raid56
> profile, repair during read is able to as well.
>
> Although the mirror num in raid56 senario has different meanings, i.e.
(typo: scenario)
> 0 or 1: read data directly
> > 1: do recover with parity,
> it could be fit into how we repair bad block during read.
Could we possibly add some symbolic names for the RAID56 case?
>
> The trick is to use BTRFS_MAP_READ instead of BTRFS_MAP_WRITE to get the
> device and position on it.
Please also document the trick in the code before the following.
> + if (btrfs_is_parity_mirror(map_tree, logical, length, mirror_num)) {
> + /* use BTRFS_MAP_READ to get the phy dev and sector */
> + ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, logical,
> + &map_length, &bbio, 0);
> + if (ret) {
> + btrfs_bio_counter_dec(fs_info);
> + bio_put(bio);
> + return -EIO;
> + }
> + ASSERT(bbio->mirror_num == 1);
> + } else {
> + ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, logical,
> + &map_length, &bbio, mirror_num);
> + if (ret) {
> + btrfs_bio_counter_dec(fs_info);
> + bio_put(bio);
> + return -EIO;
> + }
> + BUG_ON(mirror_num != bbio->mirror_num);
> }
> - BUG_ON(mirror_num != bbio->mirror_num);
> - sector = bbio->stripes[mirror_num-1].physical >> 9;
> +
> + sector = bbio->stripes[bbio->mirror_num - 1].physical >> 9;
> bio->bi_iter.bi_sector = sector;
> - dev = bbio->stripes[mirror_num-1].dev;
> + dev = bbio->stripes[bbio->mirror_num - 1].dev;
> btrfs_put_bbio(bbio);
> if (!dev || !dev->bdev || !dev->writeable) {
> btrfs_bio_counter_dec(fs_info);
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