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Re: [PATCH 1/9] btrfs: Add support for reading a filesystem with a RAID
From: |
Goffredo Baroncelli |
Subject: |
Re: [PATCH 1/9] btrfs: Add support for reading a filesystem with a RAID 5 or RAID 6 profile. |
Date: |
Thu, 14 Jun 2018 20:55:00 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 |
On 06/14/2018 01:17 PM, Daniel Kiper wrote:
> On Sun, Jun 03, 2018 at 08:53:40PM +0200, Goffredo Baroncelli wrote:
>> Signed-off-by: Goffredo Baroncelli <address@hidden>
>> ---
>> grub-core/fs/btrfs.c | 70 ++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 70 insertions(+)
>>
>> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
>> index be195448d..4d418859b 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 +766,74 @@ 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;
>> + }
>> +
>> + /*
>> + * Below is an example of a RAID 6 layout and the meaning of the
>> + * variables. The same applies to RAID 5. The only differences is
>> + * that there is only one parity disk instead of two.
>> + *
>> + * A RAID 6 layout consists of several stripes spread
>> + * on the disks, following a layout like the one below
>> + *
>> + * Disk1 Disk2 Disk3 Ddisk4
>
> Numbering seems confusing to me. I think that it should be
> 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.
>> + * In the code below:
>> + * - stripe_nr is the stripe number not considering the parities
>> + * (A1=0, B1=1, A2 = 2, B2 = 3, ...),
>
> Please be consistent. A1 = 0, B1 = 1, A2 = 2, B2 = 3, ...
>
>> + * - high is the row number (0 for A1...Q1, 1 for Q2..P2, ...),
>
> Ditto. Please always use "..." not "..".
>
>> + * - stripen is the column number (or disk number),
>
> AIUI starting from 0. Right? If yes then I think that
> drawing above requires disks/columns renumbering.
right
>
>> + * - off is the logical address to read (from the beginning of
>> + * the chunk space),
>
> s/chunk space/chunk/?
>
>> + * - chunk_stripe_length is the size of a stripe (typically 64k),
>> + * - nstripes is the number of disks,
>> + * - low is the offset of the data inside a stripe,
>> + * - stripe_offset is the offset from the beginning of the chunk
>> + * disks physical address,
>
> I am not sure that I understand. Could clarify this?
- stripe_offset is the offset (in bytes) from the beginning of the chunk
portion
stored on disk.
You can think "stripe_offset" as the "row" in the drawing, but measured in
bytes.
>
>> + * - csize is the "potential" data to read. It will be reduced to
>> + * size if the latter is smaller.
>> + */
>> + stripe_nr = grub_divmod64 (off, chunk_stripe_length, &low);
>
> OK.
>
>> + /*
>> + * stripen is evaluated without considering
>> + * the parities (0 for A1, A2, A3... 1 for B1, B2...).
>> + */
>> + high = grub_divmod64 (stripe_nr, nstripes - nparities, &stripen);
>
> OK.
>
>> + /*
>> + * stripen now considers also the parities (0 for A1, 1 for A2,
>> + * 2 for A3....). The math is performed modulo number of disks.
>> + */
>> + grub_divmod64 (high + stripen, nstripes, &stripen);
>
> OK.
>
>> + stripe_offset = low + chunk_stripe_length * high;
>
> Hmmm... I am confused. What does it mean?
>
> Daniel
>
> _______________________________________________
> Grub-devel mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/grub-devel
>
--
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
- [PATCH V5] Add support for BTRFS raid5/6 to GRUB, Goffredo Baroncelli, 2018/06/03
- [PATCH 2/9] btrfs: Add helper to check the btrfs header., Goffredo Baroncelli, 2018/06/03
- [PATCH 5/9] btrfs: Move logging code in grub_btrfs_read_logical(), Goffredo Baroncelli, 2018/06/03
- [PATCH 6/9] btrfs: Refactor the code that read from disk, Goffredo Baroncelli, 2018/06/03
- [PATCH 7/9] btrfs: Add support for recovery for a RAID 5 btrfs profiles., Goffredo Baroncelli, 2018/06/03