[blkback] blkback statistic counters are signed values

[Zoltan Kiss <zoltan.kiss@citrix.com>]

Hi,

One of our colleagues spotted a problem in xentop. Sometimes the 
VBD_WSECT value suddenly becomes unreasonably high, and it turned out 
xentop reads 
/sys/bus/xen-backend/devices/vbd-(domid)-(devID)/statistics/wr_sect into 
an unsigned long long. That value is exposed by blkback, and among other 
stat counters, it's a signed integer:

drivers/block/xen-blkback/common.h
struct xen_blkif {
...
	int			st_rd_req;
	int			st_wr_req;
	int			st_oo_req;
	int			st_f_req;
	int			st_ds_req;
	int			st_rd_sect;
	int			st_wr_sect;


I don't think these values should be negative ever, but when they 
overflow (which happens eventually), they do, and this leads to bad 
conversion in xentop.
I think the best solution would be to change the above mentioned values 
to unsigned long long as well. Any comments on that?

Regards,

Zoltan Kiss