On Fri, May 22, 2009 6:10 pm, Xu Yuehai wrote:

I know that if the read request of raid5 is handled by
chunk_aligned_read, there is no error handling in raid5. But, if this
read request is not aligned, that's say, raid5 need stripe_head to
deal with this request. I find in the code of 2.6.27 that there is no
error handling if this read request fail, I remember in older kernel,
some operations should be done such as compute_block. Am I right?

If chunk_aligned_read results in an error, then the request
is re-tried through the stripe cache.  I would call that "error handling".

If the cache finds that a drives is failed, the data is calculated
from the other drives, though the code is not a straight forward
as it used to be.
See fetch_block5 which sets STRIPE_OP_COMPUTE_BLK which causes
ops_run_compute5 to do the work (or to schedule the work on separate
hardware).

NeilBrown