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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Mar 04, 2013 at 03:54:42PM +0000, Zoltan Kiss wrote:
> 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?

Seems like the right approach. Could you send a patch please?

Thought that won't solve the problem when we overflow an 'unsigned long long'.

> 
> Regards,
> 
> Zoltan Kiss
> 
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> 

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