On 14/04/2021 03:33, Naohiro Aota wrote:
> This commit adds zone-aware magics and probing functions for zoned btrfs.
>
> Superblock (and its copies) is the only data structure in btrfs with a
The superblock?
> fixed location on a device. Since we cannot overwrite in a sequential write
cannot do overwrites
> required zone, we cannot place superblock in the zone.
the superblock
>
> Thus, zoned btrfs use superblock log writing to update superblock on
Thus, zoned btrfs uses superblock log writing to update superblocks on
> sequential write required zones. It uses two zones as a circular buffer to
> write updated superblocks. Once the first zone is filled up, start writing
> into the second buffer. When both zones are filled up and before start
starting to write
> writing to the first zone again, it reset the first zone.
>
> We can determine the position of the latest superblock by reading write
reading the write pointer
> pointer information from a device. One corner case is when both zones are
> full. For this situation, we read out the last superblock of each zone and
> compare them to determine which zone is older.
>
> The magics can detect a superblock magic ("_BHRfs_M") at the beginning of
> zone #0 or zone #1 to see if it is zoned btrfs. When both zones are filled
> up, zoned btrfs reset the first zone to write a new superblock. If btrfs
resets
> crash at the moment, we do not see a superblock at zone #0. Thus, we need
crashes
> to check not only zone #0 but also zone #1.
>
> It also supports temporary magic ("!BHRfS_M") in zone #0. The mkfs.btrfs
the temporary magic [...]. Mkfs.btrfs
[...]
> + * Log position:
> + * *: Special case, no superblock is written
> + * 0: Use write pointer of zones[0]
> + * 1: Use write pointer of zones[1]
> + * C: Compare super blcoks from zones[0] and zones[1], use the latest
blocks ~^
[...]
> + rep_size = sizeof(struct blk_zone_report) + sizeof(struct blk_zone) * 2;
> + rep = malloc(rep_size);
> + if (!rep)
> + return -errno;
> +
> + memset(rep, 0, rep_size);
I think Damien already pointed this out, but that's a good opportunity for
calloc().
Otherwise,
Reviewed-by: Johannes Thumshirn <[email protected]>
Tested-by: Johannes Thumshirn <[email protected]>
