erasure code: backend feature to read from all OSDs and silently discard EIO if possible

Bug: http://tracker.ceph.com/issues/9943

Brief: Add osd setting osd_pool_erasure_code_subread_all. Default is false. If set it to true. Will send sub-read op to all OSD and choose the first success read result.

Signed-off-by: Wei Luo <luowei@yahoo-inc.com>
You cannot compute the chunk size in this way, you need help from the erasure coded plugin. The object is divided in stripes (4k each by default) and the erasure code plugin is asked to figure out the chunk size when given the stripe_width. The result is stored in sinfo and can be retrieved with get_chunk_size(). Am I missing something here ?