Re: [PATCH] megaraid_sas: Enable shared host tag map

[Christoph Hellwig <hch@lst.de>]

On Tue, Nov 25, 2014 at 08:33:28PM +0530, Kashyap Desai wrote:
> Just trying to understand your above comment. I see host template has new
> field called
> "reserved_tags" which is normally used by mid layer to reserved block tag
> pool for driver's internal use.
> What if driver is OK to manage internal pool without any blk tag
> dependency and do not expose actual max can queue of what FW can support.
> For example, in megaraid_sas driver FW expose max_fw_cmd = 1024 and driver
> keep some reserve (let's say 24 commands for internal use) and it just
> expose 1000 command for blk tags.  This will work for blk-mq and legacy
> blk driver. Let driver to manage whatever internal reserved it kept for
> and do not add any dependency with blk tag from above layer for those
> reserved pool.

The driver can of coure always just manage its internal tags, but that
means we need to duplicate a tag allocator in every driver.  In short
it works ok for now, but I'd rather solve the problem in a single place.