[PATCH v3 3/5] virtio-blk: describe write zeroes unmap semantics

[Stefan Hajnoczi <stefanha@redhat.com>]

Explain the meaning of the unmap flag.  The details are already covered
in the device normative section but mentioning it here makes the text
easier to understand.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 content.tex | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/content.tex b/content.tex
index 4201c7e..8ea8320 100644
--- a/content.tex
+++ b/content.tex
@@ -3983,7 +3983,9 @@ struct virtio_blk_discard_write_zeroes {
 
 \field{sector} indicates the starting offset (in 512-byte units) of the
 segment, while \field{num_sectors} indicates the number of sectors in each
-discarded range. \field{unmap} is only used for write zeroes command.
+discarded range. \field{unmap} is only used in write zeroes commands and allows
+the device to discard the specified range, provided that following reads return
+zeroes.
 
 The final \field{status} byte is written by the device: either
 VIRTIO_BLK_S_OK for success, VIRTIO_BLK_S_IOERR for device or driver
-- 
2.20.1