From: Martin K. Petersen Date: Fri, 5 Dec 2014 13:58:03 +0000 (-0500) Subject: sd: tweak discard heuristics to work around QEMU SCSI issue X-Git-Tag: fixes-v4.0-rc1~346^2~2 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=e461338b6cd4074e39a0d5fdd1dc5582fbca1520 sd: tweak discard heuristics to work around QEMU SCSI issue 7985090aa020 changed the discard heuristics to give preference to the WRITE SAME commands that (unlike UNMAP) guarantee deterministic results. Ming Lei discovered that QEMU SCSI's WRITE SAME implementation internally relied on limits that were only communicated for the UNMAP case. And therefore discard commands backed by WRITE SAME would fail. Tweak the heuristics so we still pick UNMAP in the LBPRZ=0 case and only prefer the WRITE SAME variants if the device has the LBPRZ flag set. Reported-by: Ming Lei Tested-by: Ming Lei Signed-off-by: Martin K. Petersen Acked-by: Paolo Bonzini Signed-off-by: Christoph Hellwig --- diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index fedab3c21ddf..399516925d80 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -2623,8 +2623,9 @@ static void sd_read_block_limits(struct scsi_disk *sdkp) sd_config_discard(sdkp, SD_LBP_WS16); } else { /* LBP VPD page tells us what to use */ - - if (sdkp->lbpws) + if (sdkp->lbpu && sdkp->max_unmap_blocks && !sdkp->lbprz) + sd_config_discard(sdkp, SD_LBP_UNMAP); + else if (sdkp->lbpws) sd_config_discard(sdkp, SD_LBP_WS16); else if (sdkp->lbpws10) sd_config_discard(sdkp, SD_LBP_WS10);