[PATCH 9/9] btrfs: Add RAID 6 recovery for a btrfs filesystem.

[Goffredo Baroncelli]

From: Goffredo Baroncelli <address@hidden>

Add the RAID 6 recovery, in order to use a RAID 6 filesystem even if some
disks (up to two) are missing. This code use the md RAID 6 code already
present in grub.

Signed-off-by: Goffredo Baroncelli <address@hidden>
---
 grub-core/fs/btrfs.c | 63 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 6 deletions(-)

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
index db8df0eea..b49f714ef 100644
--- a/grub-core/fs/btrfs.c
+++ b/grub-core/fs/btrfs.c
@@ -30,6 +30,7 @@
 #include <grub/i18n.h>
 #include <grub/btrfs.h>
 #include <grub/crypto.h>
+#include <grub/diskfilter.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -702,11 +703,36 @@ rebuild_raid5 (char *dest, struct raid56_buffer *buffers,
     }
 }
 
+static grub_err_t
+raid6_recover_read_buffer (void *data, int disk_nr,
+                          grub_uint64_t addr __attribute__ ((unused)),
+                          void *dest, grub_size_t size)
+{
+    struct raid56_buffer *buffers = data;
+
+    if (!buffers[disk_nr].data_is_valid)
+       return grub_errno = GRUB_ERR_READ_ERROR;
+
+    grub_memcpy(dest, buffers[disk_nr].buf, size);
+
+    return grub_errno = GRUB_ERR_NONE;
+}
+
+static void
+rebuild_raid6 (struct raid56_buffer *buffers, grub_uint64_t nstripes,
+               grub_uint64_t csize, grub_uint64_t parities_pos, void *dest,
+               grub_uint64_t stripen)
+
+{
+  grub_raid6_recover_gen (buffers, nstripes, stripen, parities_pos,
+                          dest, 0, csize, 0, raid6_recover_read_buffer);
+}
+
 static grub_err_t
 raid56_read_retry (struct grub_btrfs_data *data,
                   struct grub_btrfs_chunk_item *chunk,
-                  grub_uint64_t stripe_offset,
-                  grub_uint64_t csize, void *buf)
+                  grub_uint64_t stripe_offset, grub_uint64_t stripen,
+                  grub_uint64_t csize, void *buf, grub_uint64_t parities_pos)
 {
   struct raid56_buffer *buffers;
   grub_uint64_t nstripes = grub_le_to_cpu16 (chunk->nstripes);
@@ -777,6 +803,15 @@ raid56_read_retry (struct grub_btrfs_data *data,
       ret = GRUB_ERR_READ_ERROR;
       goto cleanup;
     }
+  else if (failed_devices > 2 && (chunk_type & GRUB_BTRFS_CHUNK_TYPE_RAID6))
+    {
+      grub_dprintf ("btrfs",
+                   "not enough disks for raid6: total %" PRIuGRUB_UINT64_T
+                   ", missing %" PRIuGRUB_UINT64_T "\n",
+                   nstripes, failed_devices);
+      ret = GRUB_ERR_READ_ERROR;
+      goto cleanup;
+    }
   else
     grub_dprintf ("btrfs",
                  "enough disks for RAID 5 rebuilding: total %"
@@ -787,7 +822,7 @@ raid56_read_retry (struct grub_btrfs_data *data,
   if (chunk_type & GRUB_BTRFS_CHUNK_TYPE_RAID5)
     rebuild_raid5 (buf, buffers, nstripes, csize);
   else
-    grub_dprintf ("btrfs", "called rebuild_raid6(), NOT IMPLEMENTED\n");
+    rebuild_raid6 (buffers, nstripes, csize, parities_pos, buf, stripen);
 
   ret = GRUB_ERR_NONE;
  cleanup:
@@ -877,9 +912,11 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
grub_disk_addr_t addr,
        unsigned redundancy = 1;
        unsigned i, j;
        int is_raid56;
+       grub_uint64_t parities_pos = 0;
 
-       is_raid56 = !!(grub_le_to_cpu64 (chunk->type) &
-                      GRUB_BTRFS_CHUNK_TYPE_RAID5);
+        is_raid56 = !!(grub_le_to_cpu64 (chunk->type) &
+                      (GRUB_BTRFS_CHUNK_TYPE_RAID5 |
+                       GRUB_BTRFS_CHUNK_TYPE_RAID6));
 
        if (grub_le_to_cpu64 (chunk->size) <= off)
          {
@@ -1011,6 +1048,9 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
grub_disk_addr_t addr,
               *    size if the latter is smaller.
               *  - nparities is the number of parities (1 for RAID5, 2 for
               *    RAID6); used only in RAID5/6 code.
+              *    size if the latter is smaller.
+              *  - parities_pos is the position of the parity in a row (
+              *    2 for P1, 3 for P2...)
               */
              stripe_nr = grub_divmod64 (off, chunk_stripe_length, &low);
 
@@ -1029,6 +1069,17 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
grub_disk_addr_t addr,
               */
              grub_divmod64 (high + stripen, nstripes, &stripen);
 
+             /*
+              * parities_pos is equal to "(high - nparities) % nstripes"
+              * (see the diagram above).
+              * However "high - nparities" might be negative (eg when high
+              * == 0) leading to an incorrect computation.
+              * Instead "high + nstripes - nparities" is always positive and
+              * in modulo nstripes is equal to "(high - nparities) % nstripes"
+              */
+             grub_divmod64 (high + nstripes - nparities, nstripes,
+                            &parities_pos);
+
              stripe_offset = low + chunk_stripe_length * high;
              csize = chunk_stripe_length - low;
 
@@ -1080,7 +1131,7 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
grub_disk_addr_t addr,
                grub_errno = GRUB_ERR_NONE;
                if (err != GRUB_ERR_NONE)
                  err = raid56_read_retry (data, chunk, stripe_offset,
-                                          csize, buf);
+                                          stripen, csize, buf, parities_pos);
              }
            if (err == GRUB_ERR_NONE)
              break;
-- 
2.19.0