On Sun, Jun 03, 2018 at 08:53:40PM +0200, Goffredo Baroncelli wrote:
> Signed-off-by: Goffredo Baroncelli <kreij...@inwind.it>
> ---
> grub-core/fs/btrfs.c | 70 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 70 insertions(+)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index be195448d..4d418859b 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 +766,74 @@ 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, stripe_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;
> + }
> +
> + /*
> + * Below is an example of a RAID 6 layout and the meaning of the
> + * variables. The same applies to RAID 5. The only differences is
> + * that there is only one parity disk instead of two.
> + *
> + * A RAID 6 layout consists of several stripes spread
> + * on the disks, following a layout like the one below
> + *
> + * Disk1 Disk2 Disk3 Ddisk4
Numbering seems confusing to me. I think that it should be
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:
> + * - stripe_nr is the stripe number not considering the parities
> + * (A1=0, B1=1, A2 = 2, B2 = 3, ...),
Please be consistent. A1 = 0, B1 = 1, A2 = 2, B2 = 3, ...
> + * - high is the row number (0 for A1...Q1, 1 for Q2..P2, ...),
Ditto. Please always use "..." not "..".
> + * - stripen is the column number (or disk number),
AIUI starting from 0. Right? If yes then I think that
drawing above requires disks/columns renumbering.
> + * - off is the logical address to read (from the beginning of
> + * the chunk space),
s/chunk space/chunk/?
> + * - chunk_stripe_length is the size of a stripe (typically 64k),
> + * - nstripes is the number of disks,
> + * - low is the offset of the data inside a stripe,
> + * - stripe_offset is the offset from the beginning of the chunk
> + * disks physical address,
I am not sure that I understand. Could clarify this?
> + * - csize is the "potential" data to read. It will be reduced to
> + * size if the latter is smaller.
> + */
> + stripe_nr = grub_divmod64 (off, chunk_stripe_length, &low);
OK.
> + /*
> + * stripen is evaluated without considering
> + * the parities (0 for A1, A2, A3... 1 for B1, B2...).
> + */
> + high = grub_divmod64 (stripe_nr, nstripes - nparities, &stripen);
OK.
> + /*
> + * stripen now considers also the parities (0 for A1, 1 for A2,
> + * 2 for A3....). The math is performed modulo number of disks.
> + */
> + grub_divmod64 (high + stripen, nstripes, &stripen);
OK.
> + stripe_offset = low + chunk_stripe_length * high;
Hmmm... I am confused. What does it mean?
Daniel
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