[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>
Signed-off-by: Daniel Kiper <address@hidden>
---
 grub-core/fs/btrfs.c | 73 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
index be195448d..933a57d3b 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 +766,77 @@ 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;
+               }
+
+             /*
+              * RAID 6 layout consists of several stripes spread over
+              * the disks, e.g.:
+              *
+              *   Disk_0  Disk_1  Disk_2  Disk_3
+              *     A0      B0      P0      Q0
+              *     Q1      A1      B1      P1
+              *     P2      Q2      A2      B2
+              *
+              * Note: placement of the parities depend on row number.
+              *
+              * Pay attention that the btrfs terminology may differ from
+              * terminology used in other RAID implementations, e.g. LVM,
+              * dm or md. The main difference is that btrfs calls contiguous
+              * block of data on a given disk, e.g. A0, stripe instead of 
chunk.
+              *
+              * The variables listed below have following meaning:
+              *   - stripe_nr is the stripe number excluding the parities
+              *     (A0 = 0, B0 = 1, A1 = 2, B1 = 3, etc.),
+              *   - high is the row number (0 for A0...Q0, 1 for Q1...P1, 
etc.),
+              *   - stripen is the disk number in a row (0 for A0, Q1, P2,
+              *     1 for B0, A1, Q2, etc.),
+              *   - off is the logical address to read,
+              *   - chunk_stripe_length is the size of a stripe (typically 64 
KiB),
+              *   - nstripes is the number of disks in 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 RAID 5, 2 for
+              *     RAID 6); used only in RAID 5/6 code.
+              */
+             stripe_nr = grub_divmod64 (off, chunk_stripe_length, &low);
+
+             /*
+              * stripen is computed without the parities
+              * (0 for A0, A1, A2, 1 for B0, B1, B2, etc.).
+              */
+             high = grub_divmod64 (stripe_nr, nstripes - nparities, &stripen);
+
+             /*
+              * The stripes are spread over the disks. Every each row their
+              * positions are shifted by 1 place. So, the real disks number
+              * change. Hence, we have to take current row number modulo
+              * nstripes into account (0 for A0, 1 for A1, 2 for A2, etc.).
+              */
+             grub_divmod64 (high + stripen, nstripes, &stripen);
+
+             stripe_offset = low + chunk_stripe_length * high;
+             csize = chunk_stripe_length - low;
+
              break;
            }
          default:
-- 
2.19.1