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

[Goffredo Baroncelli]

From: Goffredo Baroncelli <address@hidden>

Signed-off-by: Goffredo Baroncelli <address@hidden>
---
 grub-core/fs/btrfs.c | 74 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
index be195448d..9bc6d399d 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 +766,78 @@ 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 of several stripes spread on the
+              * disks, following a layout like the one below
+              *
+              *   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.
+              *  Pay attention that the BTRFS terminolgy may be different
+              *  from others RAID implementation (e.g. lvm/dm or md). In BTRFS
+              *  a contiguous block of data of a disk (like A1) is called
+              *  stripe.
+              *  In the code below:
+              *  - stripe_nr is the stripe 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 in a row (0 for A1,Q2,P3, 1 for
+              *    B1...),
+              *  - off is the logical address to read,
+              *  - chunk_stripe_length is the size of a stripe (typically 64k),
+              *  - nstripes is the number of disks of a row
+              *  - low is the offset of the data inside a stripe,
+              *  - stripe_offset is the data offset in an array,
+              *  - csize is the "potential" data to read. It will be reduced to
+              *    size if the latter is smaller.
+              *  - nparities is the number of parities (1 for RAID5, 2 for
+              *    RAID6); used only in RAID5/6 code.
+              */
+             stripe_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 (stripe_nr, nstripes - nparities, &stripen);
+
+             /*
+              * the stripes are spread across the disks, each row their
+              * position is shifted by 1 place. So to compute the real disk
+              * number occuped by a stripe, we need to sum also the
+              * "row number" in modulo nstripes (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:
-- 
2.19.0