Re: [PATCH 7/9] btrfs: add support for recovery for a RAID 5 btrfs profiles.

[Daniel Kiper]

On Wed, May 16, 2018 at 08:48:17PM +0200, Goffredo Baroncelli wrote:
> Signed-off-by: Goffredo Baroncelli <address@hidden>
> ---
>  grub-core/fs/btrfs.c | 174 ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 170 insertions(+), 4 deletions(-)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index 63651928b..5fcaad86f 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -29,6 +29,7 @@
>  #include <minilzo.h>
>  #include <grub/i18n.h>
>  #include <grub/btrfs.h>
> +#include <grub/crypto.h>
>
>  GRUB_MOD_LICENSE ("GPLv3+");
>
> @@ -666,6 +667,150 @@ btrfs_read_from_chunk (struct grub_btrfs_data *data,
>      return err;
>  }
>
> +struct raid56_buffer {
> +  void *buf;
> +  int  data_is_valid;
> +};
> +
> +static void
> +rebuild_raid5 (struct raid56_buffer *buffers, grub_uint64_t nstripes,
> +               grub_uint64_t csize)
> +{
> +  grub_uint64_t target = 0, i;
> +
> +  while (buffers[target].data_is_valid && target < nstripes)
> +    ++target;
> +
> +  if (target == nstripes)
> +    {
> +      grub_dprintf ("btrfs", "called rebuild_raid5(), but all disks are 
> OK\n");
> +      return;
> +    }
> +
> +  grub_dprintf ("btrfs", "rebuilding raid5 stripe #%" PRIuGRUB_UINT64_T "\n",
> +             target);
> +  for (i = 0; i < nstripes; i++)
> +    if (i != target)
> +      grub_crypto_xor (buffers[target].buf, buffers[target].buf, 
> buffers[i].buf,
> +                       csize);
> +}
> +
> +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 stripen,
> +                grub_uint64_t csize, void *buf)
> +{
> +
> +  struct raid56_buffer *buffers = NULL;
> +  grub_uint64_t nstripes = grub_le_to_cpu16 (chunk->nstripes);
> +  grub_uint64_t chunk_type = grub_le_to_cpu64 (chunk->type);
> +  grub_err_t ret = GRUB_ERR_NONE;
> +  grub_uint64_t i, failed_devices;
> +
> +  buffers = grub_zalloc (sizeof(*buffers) * nstripes);
> +  if (!buffers)
> +    {
> +      ret = GRUB_ERR_OUT_OF_MEMORY;
> +      goto cleanup;
> +    }
> +
> +  for (i = 0; i < nstripes; i++)
> +    {
> +      buffers[i].buf = grub_zalloc (csize);
> +      if (!buffers[i].buf)
> +     {
> +       ret = GRUB_ERR_OUT_OF_MEMORY;
> +       goto cleanup;
> +     }
> +    }
> +
> +  for (i = 0; i < nstripes; i++)
> +    {
> +      struct grub_btrfs_chunk_stripe *stripe;
> +      grub_disk_addr_t paddr;
> +      grub_device_t dev;
> +      grub_err_t err2;
> +
> +      stripe = (struct grub_btrfs_chunk_stripe *) (chunk + 1);
> +      stripe += i;
> +
> +      paddr = grub_le_to_cpu64 (stripe->offset) + stripe_offset;
> +      grub_dprintf ("btrfs", "reading paddr %" PRIxGRUB_UINT64_T
> +                    " from stripe ID %" PRIxGRUB_UINT64_T "\n", paddr,
> +                    stripe->device_id);
> +
> +      dev = find_device (data, stripe->device_id);
> +      if (!dev)
> +     {
> +       buffers[i].data_is_valid = 0;
> +       grub_dprintf ("btrfs", "stripe %" PRIuGRUB_UINT64_T " FAILED (dev ID 
> %"
> +                     PRIxGRUB_UINT64_T ")\n", i, stripe->device_id);
> +       continue;

What will happen if more than one stripe is broken?

> +     }
> +
> +      err2 = grub_disk_read (dev->disk, paddr >> GRUB_DISK_SECTOR_BITS,
> +                          paddr & (GRUB_DISK_SECTOR_SIZE - 1),
> +                          csize, buffers[i].buf);
> +      if (err2 == GRUB_ERR_NONE)
> +     {
> +       buffers[i].data_is_valid = 1;
> +       grub_dprintf ("btrfs", "stripe %" PRIuGRUB_UINT64_T " Ok (dev ID %"
> +                     PRIxGRUB_UINT64_T ")\n", i, stripe->device_id);
> +     }
> +      else
> +     {
> +       buffers[i].data_is_valid = 0;
> +       grub_dprintf ("btrfs", "stripe %" PRIuGRUB_UINT64_T
> +                     " FAILED (dev ID %" PRIxGRUB_UINT64_T ")\n", i,
> +                     stripe->device_id);

Ditto?

> +     }
> +    }
> +
> +  failed_devices = 0;
> +  for (i = 0; i < nstripes; i++)
> +    if (!buffers[i].data_is_valid)
> +      ++failed_devices;
> +  if (failed_devices > 1 && (chunk_type & GRUB_BTRFS_CHUNK_TYPE_RAID5))
> +    {
> +      grub_dprintf ("btrfs",
> +                 "not enough disks for raid5: total %" PRIuGRUB_UINT64_T

s/raid5/RAID5/ Please fix this and the rest of messages in the other patches.

> +                 ", missing %" PRIuGRUB_UINT64_T "\n",
> +                 nstripes, failed_devices);
> +      ret = GRUB_ERR_READ_ERROR;
> +      goto cleanup;

Ahhh... Here it is! Perfect!

> +    }
> +  else
> +    {
> +      grub_dprintf ("btrfs",
> +                    "enough disks for raid5/6 rebuilding: total %"

s#raid5/6#RAID5# This is the patch for RAID 5. Right?
Please do not mix RAID 5 changes with RAID 6 changes.

> +                 PRIuGRUB_UINT64_T ", missing %" PRIuGRUB_UINT64_T "\n",
> +                    nstripes, failed_devices);
> +    }
> +
> +  /* if these are enough, try to rebuild the data */
> +  if (chunk_type & GRUB_BTRFS_CHUNK_TYPE_RAID5)
> +    {
> +      rebuild_raid5 (buffers, nstripes, csize);
> +      grub_memcpy (buf, buffers[stripen].buf, csize);

Hmmm... Do we need this grub_memcpy()? Why rebuild_raid5() could
not fill buf directly? If it is not possible then I think that
grub_memcpy() should be called from rebuild_raid5().

> +    }
> +  else
> +    {
> +      grub_dprintf ("btrfs", "called rebuild_raid6(), NOT IMPLEMENTED\n");
> +    }

Please drop this curly brackets.

> +
> +cleanup:

Space before the label please.

> +  if (buffers)
> +    {
> +      for (i = 0; i < nstripes; i++)
> +     if (buffers[i].buf)
> +       grub_free(buffers[i].buf);
> +      grub_free(buffers);
> +    }
> +
> +  return ret;
> +}
> +
>  static grub_err_t
>  grub_btrfs_read_logical (struct grub_btrfs_data *data, grub_disk_addr_t addr,
>                        void *buf, grub_size_t size, int recursion_depth)
> @@ -743,6 +888,11 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
> grub_disk_addr_t addr,
>       grub_uint16_t nstripes;
>       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);

OK, I would leave this as is. However, I would mention
in the commit message that this patch also do some minor
preparatory work for RAID 6 support.

>
>       if (grub_le_to_cpu64 (chunk->size) <= off)
>         {
> @@ -885,6 +1035,8 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
> grub_disk_addr_t addr,
>              * number of disks
>              */
>             grub_divmod64 (high + stripen, nstripes, &stripen);
> +           grub_divmod64 (high + nstripes - nparities, nstripes,
> +                          &parities_pos);
>
>             stripe_offset = low + chunk_stripe_length * high;
>             csize = chunk_stripe_length - low;
> @@ -917,15 +1069,29 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
> grub_disk_addr_t addr,
>           grub_dprintf ("btrfs", "reading laddr 0x%" PRIxGRUB_UINT64_T "\n",
>                         addr);
>
> -         for (i = 0; i < redundancy; i++)
> +         if (!is_raid56)
> +           {
> +             for (i = 0; i < redundancy; i++)
> +               {
> +                 err = btrfs_read_from_chunk (data, chunk, stripen,
> +                                              stripe_offset,
> +                                              i,     /* redundancy */
> +                                              csize, buf);
> +                 if (err == GRUB_ERR_NONE)
> +                     break;
> +               }
> +           }
> +         else
>             {
>               err = btrfs_read_from_chunk (data, chunk, stripen,
>                                            stripe_offset,
> -                                          i,     /* redundancy */
> +                                          0,     /* no mirror */
>                                            csize, buf);

I do not understand this change... Why?

> -             if (err == GRUB_ERR_NONE)
> -                 break;
> +             if (err != GRUB_ERR_NONE)
> +               err = raid56_read_retry (data, chunk, stripe_offset,
> +                                        stripen, csize, buf);

I have a feeling that this change is somehow related to my comment
for patch #6.

>             }
> +

Drop this change please.

>           if (err == GRUB_ERR_NONE)
>               break;
>         }

Daniel