On 29.09.2016 10:10, Fam Zheng wrote: > On Thu, 09/29 09:58, Paolo Bonzini wrote: >> >> >> On 29/09/2016 04:21, Fam Zheng wrote: >>> On Wed, 09/28 18:11, Max Reitz wrote: >>>> Note that BDRV_REQ_MAY_UNMAP does not mean "Yes, please discard" but >>>> just "You may discard if it's easier for you". But it's actually not >>>> easier for us, so I don't see why we're doing it. >>>> >>>> As far as I can guess you actually want some way to tell a block driver >>>> to actually make an effort to discard clusters as long they then read >>>> back as zero (which is why you cannot simply use bdrv_pdiscard()). >>>> However, I think this would require a new flag called >>>> BDRV_REQ_SHOULD_UNMAP (which should imply BDRV_REQ_MAY_UNMAP). >>> >>> This flag doesn't make sense to me, if the protocol doesn't know how to >>> unmap, >>> it can ignore BDRV_REQ_MAY_UNMAP, but not BDRV_REQ_SHOULD_UNMAP. It just >>> complicates things a little. >> >> I don't think we actually have a use for a "MAY" unmap flag. Either we >> keep the not-so-perfect name or we replace MAY_UNMAP with "should" or >> "want" or "would_like" unmap... But Fam's patch does do what was >> intended for the flag (which is the equivalent of the UNMAP bit in the >> SCSI WRITE SAME command). > > After reading rfc2119, now I agree that "SHOULD" is better. :)
That's OK with me, then. Max
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