Matthew Wilcox wrote:
(3) when creating a discard request, use block helpers w/ queue-specific
knowledge to create either
(a) one request, REQ_TYPE_FS, with discard flag or
(b) two requests, REQ_TYPE_FS followed by REQ_TYPE_DISCARD
I'm not sure we need option 3b.
Well -- it is a hard requirement to map 1:1 struct request with the
underlying hardware device's command set.
If a device command set lacks a READ-and-DISCARD operation, then you
_must_ create two struct request. Otherwise you break block layer
tagging and other 1:1-based assumptions that exist today.
Thus, given that all of ATA|SCSI|NVMHCI have a DISCARD operation
distinct from other commands...
option 3b is the overwhelming common case.
Jeff
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