On Wed, 2017-05-10 at 16:06 +0200, hch@xxxxxx wrote: > On Mon, May 08, 2017 at 11:46:14PM -0700, Nicholas A. Bellinger wrote: > > That said, simply propagating up q->limits.max_write_zeroes_sectors as > > dev_attrib->unmap_zeroes_data following existing code still looks like > > the right thing to do. > > It is not. Martin has decoupled write same/zeroes support from discard > support. Any device will claim to support it initially, and we'll > only clear the flag if a Write Same command fails. > > So even if LBPRZ is not set you can trivially get into a situation > where discard is supported through UNMAP, and you'll incorrectly > set LBPRZ and will cause data corruption. In that case, there are two choices. 1) Expose a block_device or request_queue bit to signal 'real LBPRZ' support up to IBLOCK, in order to maintain SCSI target feature compatibility. 2) Or drop the LBPRZ bit usage for IBLOCK all-together. Since I happen happen to support a block driver that has 'real LBPRZ' support for all discards, I'd prefer the latter so this doesn't have to be carried out-of-tree. So what are the options for this in post v4.12..?
