On 05/09/2018 03:46 PM, Daniel Kiper wrote:
> On Tue, Apr 24, 2018 at 09:13:10PM +0200, Goffredo Baroncelli wrote:
>> Signed-off-by: Goffredo Baroncelli <kreij...@inwind.it>
>> ---
>> grub-core/fs/btrfs.c | 32 ++++++++++++++++++++++++++++++++
>> 1 file changed, 32 insertions(+)
>>
>> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
>> index be195448d..b0032ea46 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
>
> #define GRUB_BTRFS_CHUNK_TYPE_RAID5 0x80
> #define GRUB_BTRFS_CHUNK_TYPE_RAID6 0x100
> Please start in one column... ----> ^^^^^
OK
>
>> grub_uint8_t dummy2[0xc];
>> grub_uint16_t nstripes;
>> grub_uint16_t nsubstripes;
>> @@ -764,6 +766,36 @@ 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;
>> + grub_uint64_t stripe_nr, high;
>> + grub_uint64_t low;
>
> Could you define all in one line?
Ok
>
>> + 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;
>> + }
>> +
>> + stripe_nr = grub_divmod64 (off, chunk_stripe_length, &low);
>
> This is clear for me...
I want to put this comment before the line above
/*
* A raid 6 layout consists in several stripes spread
* on the disks, following a layout like the one below
*
* Disk1 Disk2 Disk3 Ddisk4
*
* A1 B1 P1 Q1
* Q2 A2 B2 P2
* P3 Q3 A3 B3
* [...]
*
* Note that the placement of the parities depends by the row
* In the code below:
* stripe_nr -> is the stripe number not considering 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 column number (or number of disk)
* off -> logical address to read (from teh beginning of the
* chunk space)
* chunk_stripe_length -> size of a stripe (typically 64k)
* nstripes -> number of disks
*
*/
>
>> + high = grub_divmod64 (stripe_nr, nstripes - nparities, &stripen);
then I want to put here
/*
* until now stripen is evaluated without the parities (0 for A1,
* A2, A3... 1 for B1, B2...); now consider also the parities (0
* for A1, 1 for A2, 2 for A3....); the math is done "modulo"
* number of disk
*/
>> + grub_divmod64 (high + stripen, nstripes, &stripen);
>
> ... but not these two. Could you enlighten me?
It is more clear ? To understand this I spent a lot of time dumping the raw
data on the disks; this because in wikipedia there is another stripe layout
(A1, B1, B2 always on the first column; however btrfs does this different)
>> + stripe_offset = low + chunk_stripe_length * high;
>
> ???
This is like the other RAID profile: high is the "row number" of the stripe
matrix; so stripe_offset is the start of the data from the begin of the chunk
(on the disk)
>
>> + csize = chunk_stripe_length - low;
>
> Chunk size to read?
This is like the other code. We can read until the end of the stripe. Then the
disks will change.
>
> Daniel
>
--
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
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