Re: New TRIM/UNMAP tree published (2009-05-02)

[Jeff Garzik]

Jeff Garzik wrote:
> (2) determine at init if queue (a) supports explicit DISCARD and/or (b) 
> supports DISCARD flag passed with READ or WRITE


As an aside -- does any existing command set support case #b, above?

AFAICT, ATA, SCSI and NVMHCI all have a single, explicit hardware 
command to discard/deallocate unused sectors.

Therefore, creating REQ_TYPE_DISCARD seems to eliminate any need for new 
hook ->prepare_discard().

This provides a 1:1 correspondence between hardware and struct request, 
most closely matching the setup of known hardware.

	Jeff



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