Re: [Xen-devel] [PATCH V5 2/5] Add XEN pvSCSI protocol description

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Fri, Aug 22, 2014 at 06:18:03AM +0200, Juergen Gross wrote:
> >>The resulting number of struct scsiif_request_segment is the sum of
> >>seg[0..nr_segments-1].length / sizeof(struct scsiif_request_segment).
> >>
> >
> >Where the nr_segments can only go Up to VSCSIIF_SG_TABLESIZE, so the max
> >total SG entries you can is 13312 ( 4096 / 8 = 512 max per page, times
> >26).
> 
> In theory, yes. SG_ALL (being 128 today) is limiting this value.

Note that SG_ALL (or SCSI_MAX_SG_SEGMENTS which is a better name for it)
is only the maximum if your driver doesn't support S/G chaining.  Given
that it and the Xen infrastructure seems to use the proper s/g list
helpers it should support SCSI_MAX_SG_CHAIN_SEGMENTS easily.

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