Re: [Xen-devel] about blkfront.c

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> Sorry for the dumb question,
> 
> I noticed that in the function blkfront.c: blkif_queue_request(...), there
> are these two lines of codes:
> 
> ----------------------------
>   if ( lsect > 7 )
>         BUG();
> ----------------------------

Disk sectors are 512 bytes, pages 4096 bytes, hence you can have
runs of up to 8 sectors in a page. At the point that
queue_request is called we know that the request will fit
entirely within a page. It's the job of this function to merge
requests that are to sequential areas of disk into in a single
scatter gather list. 

Ian


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