Re: [PATCH 9/9] btrfs: Add RAID 6 recovery for a btrfs filesystem.

[Daniel Kiper]

On Tue, Jun 19, 2018 at 07:39:56PM +0200, Goffredo Baroncelli wrote:
> Add the RAID 6 recovery, in order to use a RAID 6 filesystem even if some
> disks (up to two) are missing. This code use the md RAID 6 code already
> present in grub.
>
> Signed-off-by: Goffredo Baroncelli <address@hidden>
> ---
>  grub-core/fs/btrfs.c | 51 ++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 45 insertions(+), 6 deletions(-)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index 7f01e447a..13777c868 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -30,6 +30,7 @@
>  #include <grub/i18n.h>
>  #include <grub/btrfs.h>
>  #include <grub/crypto.h>
> +#include <grub/diskfilter.h>
>
>  GRUB_MOD_LICENSE ("GPLv3+");
>
> @@ -705,11 +706,36 @@ rebuild_raid5 (char *dest, struct raid56_buffer 
> *buffers,
>      }
>  }
>
> +static grub_err_t
> +raid6_recover_read_buffer (void *data, int disk_nr,
> +                        grub_uint64_t addr __attribute__ ((unused)),
> +                        void *dest, grub_size_t size)
> +{
> +    struct raid56_buffer *buffers = data;
> +
> +    if (!buffers[disk_nr].data_is_valid)
> +     return grub_errno = GRUB_ERR_READ_ERROR;
> +
> +    grub_memcpy(dest, buffers[disk_nr].buf, size);
> +
> +    return grub_errno = GRUB_ERR_NONE;
> +}
> +
> +static void
> +rebuild_raid6 (struct raid56_buffer *buffers, grub_uint64_t nstripes,
> +               grub_uint64_t csize, grub_uint64_t parities_pos, void *dest,
> +               grub_uint64_t stripen)
> +
> +{
> +  grub_raid6_recover_gen (buffers, nstripes, stripen, parities_pos,
> +                          dest, 0, csize, 0, raid6_recover_read_buffer);
> +}
> +
>  static grub_err_t
>  raid56_read_retry (struct grub_btrfs_data *data,
>                  struct grub_btrfs_chunk_item *chunk,
> -                grub_uint64_t stripe_offset,
> -                grub_uint64_t csize, void *buf)
> +                grub_uint64_t stripe_offset, grub_uint64_t stripen,
> +                grub_uint64_t csize, void *buf, grub_uint64_t parities_pos)
>  {
>    struct raid56_buffer *buffers = NULL;
>    grub_uint64_t nstripes = grub_le_to_cpu16 (chunk->nstripes);
> @@ -788,6 +814,15 @@ raid56_read_retry (struct grub_btrfs_data *data,
>        ret = GRUB_ERR_READ_ERROR;
>        goto cleanup;
>      }
> +  else if (failed_devices > 2 && (chunk_type & GRUB_BTRFS_CHUNK_TYPE_RAID6))
> +    {
> +      grub_dprintf ("btrfs",
> +                 "not enough disks for raid6: total %" PRIuGRUB_UINT64_T
> +                 ", missing %" PRIuGRUB_UINT64_T "\n",
> +                 nstripes, failed_devices);
> +      ret = GRUB_ERR_READ_ERROR;
> +      goto cleanup;
> +    }
>    else
>      {
>        grub_dprintf ("btrfs",
> @@ -800,7 +835,7 @@ raid56_read_retry (struct grub_btrfs_data *data,
>    if (chunk_type & GRUB_BTRFS_CHUNK_TYPE_RAID5)
>      rebuild_raid5 (buf, buffers, nstripes, csize);
>    else
> -    grub_dprintf ("btrfs", "called rebuild_raid6(), NOT IMPLEMENTED\n");
> +    rebuild_raid6 (buffers, nstripes, csize, parities_pos, buf, stripen);
>
>   cleanup:
>    if (buffers)
> @@ -892,9 +927,11 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
> grub_disk_addr_t addr,
>       unsigned redundancy = 1;
>       unsigned i, j;
>       int is_raid56;
> +     grub_uint64_t parities_pos = 0;
>
> -     is_raid56 = !!(grub_le_to_cpu64 (chunk->type) &
> -                    GRUB_BTRFS_CHUNK_TYPE_RAID5);
> +        is_raid56 = !!(grub_le_to_cpu64 (chunk->type) &
> +                    (GRUB_BTRFS_CHUNK_TYPE_RAID5 |
> +                     GRUB_BTRFS_CHUNK_TYPE_RAID6));
>
>       if (grub_le_to_cpu64 (chunk->size) <= off)
>         {
> @@ -1039,6 +1076,8 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
> grub_disk_addr_t addr,
>              * 2 for A3....). The math is performed modulo number of disks.
>              */
>             grub_divmod64 (high + stripen, nstripes, &stripen);
> +           grub_divmod64 (high + nstripes - nparities, nstripes,
> +                          &parities_pos);

This change suggest that this line does not belong to patch #1.
And you have to add parities_pos to the comment above too.

Daniel