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[Xen-devel] [blkback] blkback statistic counters are signed values


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:

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?


Zoltan Kiss

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