On Tue, 2017-05-02 at 09:23 +0200, hch@lst.de wrote:

On Tue, May 02, 2017 at 12:16:13AM -0700, Nicholas A. Bellinger wrote:

quoted

Or, another options is use bdev_write_zeroes_sectors() to determine when
dev_attrib->unmap_zeroes_data should be set.

Yes, that in combination with your patch to use bdev_write_zeroes_sectors
for zeroing from write same seems like the right fix.

The larger target/iblock conversion patch looks like post v4.12 material
at this point, so to avoid breakage wrt to existing LBPRZ behavior, I'll
plan to push the following patch post -rc1.

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index d2f089c..e7caf78 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c

@@ -851,7 +851,7 @@ bool target_configure_unmap_from_queue(struct se_dev_attrib *attrib,
        attrib->unmap_granularity = q->limits.discard_granularity / block_size;
        attrib->unmap_granularity_alignment = q->limits.discard_alignment /
                                                                block_size;
-       attrib->unmap_zeroes_data = 0;
+       attrib->unmap_zeroes_data = (q->limits.max_write_zeroes_sectors);
        return true;
 }
 EXPORT_SYMBOL(target_configure_unmap_from_queue);