[PATCH 2/4] virtio-blk: clarify what seg_max and size_max are for

[Paolo Bonzini <pbonzini@redhat.com>]

Define them in terms of descriptors, not segments, and explain what the
driver and device are to use them for.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 content.tex | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/content.tex b/content.tex
index 4cdfeef..fd3a3c2 100644
--- a/content.tex
+++ b/content.tex
@@ -3515,11 +3515,11 @@ device except where noted.
 \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits}
 
 \begin{description}
-\item[VIRTIO_BLK_F_SIZE_MAX (1)] Maximum size of any single segment is
-    in \field{size_max}.
+\item[VIRTIO_BLK_F_SIZE_MAX (1)] Maximum size of any single descriptor in
+    the data portion of a request ("segment") is in \field{size_max}.
 
-\item[VIRTIO_BLK_F_SEG_MAX (2)] Maximum number of segments in a
-    request is in \field{seg_max}.
+\item[VIRTIO_BLK_F_SEG_MAX (2)] Maximum number of descriptors in the
+    data portion of a request ("segments") is in \field{seg_max}.
 
 \item[VIRTIO_BLK_F_GEOMETRY (4)] Disk-style geometry specified in
     \field{geometry}.
@@ -3762,6 +3762,10 @@ error or VIRTIO_BLK_S_UNSUPP for a request unsupported by device:
 A driver SHOULD NOT submit a request which would cause a read or write
 beyond \field{capacity}.
 
+A driver SHOULD NOT submit a request which has more than \field{seg_max}
+descriptors in the data portion, or which has more than \field{size_max}
+bytes in a single descriptor in the data portion.
+
 A driver SHOULD accept the VIRTIO_BLK_F_RO feature if offered.
 
 A driver MUST set \field{sector} to 0 for a VIRTIO_BLK_T_FLUSH request.
@@ -3782,6 +3786,11 @@ a range of sectors has been discarded.
 A device MUST set the \field{status} byte to VIRTIO_BLK_S_IOERR for a
 request which would cause a read or write beyond \field{capacity}.
 
+A device MAY set the \field{status} byte to VIRTIO_BLK_S_IOERR for a
+request which has more than \field{seg_max} descriptors in the data
+portion, or which has more than \field{size_max} bytes in a single
+descriptor in the data portion.
+
 A device MUST set the \field{status} byte to VIRTIO_BLK_S_IOERR
 for a write request if the VIRTIO_BLK_F_RO feature if offered, and MUST NOT
 write any data.
-- 
2.17.1