Re: Regarding RAID0 Code

On Saturday January 1, poonamsbox@yahoo.com wrote:

Respected Sir,
 
            I am a student from India. I am studying the RAID 0 code
            in the linux kernel 2.4.20. I got some problems in
            understanding the code, especially in the
            raid0_make_request function. I didnt understand the
            following statements.. like why the anding is done, and
            what is sect_in_chunk. Please if you could tell me the
            details, it would be a very great help for me. Please
            sir, hoping for some help. 
 
258         sect_in_chunk = bh->b_rsector & ((chunk_size<<1) -1);
259         chunk = (block - zone->zone_offset) / (zone->nb_dev << chunksize_bits);
260         tmp_dev = zone->dev[(block >> chunksize_bits) % zone->nb_dev];
261         rsect = (((chunk << chunksize_bits) + zone->dev_offset)<<1)
262                 + sect_in_chunk;

"sect_in_chunk" is the number of the target sector within it's chunk.
i.e. the remainder when the target sector is divided by the chunk
size.

If it still doesn't make sense, try writing the code for mapping an
array sector number to a (device number + device sector number).  Then
ask specifically about differences.

NeilBrown

               Thanking you in anticipation.
 
With Regards,
Poonam Dalya,
PICT,Pune,
INDIA.