Re: [PATCH 1/9] btrfs: Add support for reading a filesystem with a RAID 5 or RAID 6 profile.

[Goffredo Baroncelli]

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On 19/09/2018 20.36, Goffredo Baroncelli wrote:
> From: Goffredo Baroncelli <address@hidden>
> 
> Signed-off-by: Goffredo Baroncelli <address@hidden>
> ---
>  grub-core/fs/btrfs.c | 66 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 66 insertions(+)
> 
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index be195448d..56c42746d 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -119,6 +119,8 @@ struct grub_btrfs_chunk_item
>  #define GRUB_BTRFS_CHUNK_TYPE_RAID1         0x10
>  #define GRUB_BTRFS_CHUNK_TYPE_DUPLICATED    0x20
>  #define GRUB_BTRFS_CHUNK_TYPE_RAID10        0x40
> +#define GRUB_BTRFS_CHUNK_TYPE_RAID5         0x80
> +#define GRUB_BTRFS_CHUNK_TYPE_RAID6         0x100
>    grub_uint8_t dummy2[0xc];
>    grub_uint16_t nstripes;
>    grub_uint16_t nsubstripes;
> @@ -764,6 +766,70 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
> grub_disk_addr_t addr,
>             stripe_offset = low + chunk_stripe_length
>               * high;
>             csize = chunk_stripe_length - low;
> +           break;
> +         }
> +       case GRUB_BTRFS_CHUNK_TYPE_RAID5:
> +       case GRUB_BTRFS_CHUNK_TYPE_RAID6:
> +         {
> +           grub_uint64_t nparities, block_nr, high, low;
> +
> +           redundancy = 1;   /* no redundancy for now */
> +
> +           if (grub_le_to_cpu64 (chunk->type) & GRUB_BTRFS_CHUNK_TYPE_RAID5)
> +             {
> +               grub_dprintf ("btrfs", "RAID5\n");
> +               nparities = 1;
> +             }
> +           else
> +             {
> +               grub_dprintf ("btrfs", "RAID6\n");
> +               nparities = 2;
> +             }
> +
> +           /*
> +            * A RAID 6 layout consists of several blocks spread on the disks.
> +            * The raid terminology is used to call all the blocks of a row
> +            * "stripe". Unfortunately the BTRFS terminology confuses block
> +            * and stripe.
> +            *
> +            *   Disk0  Disk1  Disk2  Disk3
> +            *
> +            *    A1     B1     P1     Q1
> +            *    Q2     A2     B2     P2
> +            *    P3     Q3     A3     B3
> +            *  [...]
> +            *
> +            *  Note that the placement of the parities depends on row index.
> +            *  In the code below:
> +            *  - block_nr is the block number without the parities
> +            *    (A1 = 0, B1 = 1, A2 = 2, B2 = 3, ...),
> +            *  - high is the row number (0 for A1...Q1, 1 for Q2...P2, ...),
> +            *  - stripen is the disk number (0 for A1,Q2,P3, 1 for B1...),
> +            *  - off is the logical address to read
> +            *  - chunk_stripe_length is the size of a block (typically 64k),
> +            *  - nstripes is the number of disks,
> +            *  - low is the offset of the data inside a stripe,
> +            *  - stripe_offset is the disk offset,
> +            *  - csize is the "potential" data to read. It will be reduced to
> +            *    size if the latter is smaller.
> +            */
> +           block_nr = grub_divmod64 (off, chunk_stripe_length, &low);
> +
> +           /*
> +            * stripen is computed without the parities (0 for A1, A2, A3...
> +            * 1 for B1, B2...).
> +            */
> +           high = grub_divmod64 (block_nr, nstripes - nparities, &stripen);
> +
> +           /*
> +            * stripen is recomputed considering the parities (0 for A1, 1 for
> +            * A2, 2 for A3....).
> +            */
> +           grub_divmod64 (high + stripen, nstripes, &stripen);
> +
> +           stripe_offset = low + chunk_stripe_length * high;
> +           csize = chunk_stripe_length - low;
> +
>             break;
>           }
>         default:
> 


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gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
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