On Fri, May 11, 2018 at 09:24:39PM +0200, Goffredo Baroncelli wrote:
> Signed-off-by: Goffredo Baroncelli <kreij...@inwind.it>
> ---
> grub-core/fs/btrfs.c | 61 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 61 insertions(+)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index be195448d..7e287d0ec 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 +766,65 @@ 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;
> + }
> +
> + /*
> + * A raid 6 layout consists in several stripes spread
This line is confusing if you compare it with both cases a few lines above.
I think that you should explain somewhere why this math works for RAID 5
and RAID 6.
> + * on the disks, following a layout like the one below
> + *
> + * Disk1 Disk2 Disk3 Ddisk4
> + *
> + * A1 B1 P1 Q1
> + * Q2 A2 B2 P2
> + * P3 Q3 A3 B3
> + * [...]
> + *
> + * Note that the placement of the parities depends by the row
s/by the/on/?
> + * index;
> + * In the code below:
> + * stripe_nr -> is the stripe number not considering 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 column number (or number of disk)
s/number of disk/number of disk in row/?
> + * off -> logical address to read (from teh beginning of the
What is "teh"? nth? And it seems to me that off is the offset from the
beginning of the array.
> + * chunk space)
I am not sure what you mean by "chunk space" here.
> + * chunk_stripe_length -> size of a stripe (typically 64k)
I assume that stripe does not cover P1 and Q1 (parity disks)?
> + * nstripes -> number of disks
> + *
> + */
> + stripe_nr = grub_divmod64 (off, chunk_stripe_length, &low);
What is the low?
> + high = grub_divmod64 (stripe_nr, nstripes - nparities, &stripen);
> +
> + /*
> + * until now stripen is evaluated without the parities (0 for A1,
> + * A2, A3... 1 for B1, B2...); now consider also the parities (0
> + * for A1, 1 for A2, 2 for A3....); the math is done "modulo"
> + * number of disk
May I ask you to use proper English sentences in the comments?
Daniel
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