[Xen-devel] doubt: Block IO multiple ring protocol

[Kaushik Bhandankar <kaushikb@xxxxxxxxxxxxx>]

Hello,

Looking at linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c, I had 
following doubts (also looked at the following changeset which 
introduces multiple ring protocols: 
http://lists.xensource.com/archives/html/xen-changelog/2007-01/msg00413.html)
1) When a block IO request is made by guest, do_block_io_op() obtains 
the 'req' from appropriate ring based on blk_protocol (and invokes 
dispatch_rw_block_io()) but the "req_cons" is incremented for the 
"common" ring.. Where is the "req_cons" being incremented for the 
corresponding ring (native, x86_32 or x86_64) ?
2) For sending back the response, make_response() copies the "resp" on 
the appropriate ring based on blk_protocol but increments the 
"rsp_prod_pvt" for the "common"  ring. Where is the "rsp_prod_pvt" being 
incremented for the corresponding ring (native, x86_32 or x86_64) ?
Looking at xen/include/public/io/ring.h, I couldnt really figure things 
 out looking at the macros? Am not really sure how the counters get 
incremented/decremented for each protocol ring during block 
request/response phase ...Any hint is appreciated....
--Kaushik

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