0001-device-types-blk-description.tex-Add-feature-flag-fo.patch

gistfile1.txt

From 60e188d06d775d51e501a4c3d994eff3326c7af9 Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Fri, 31 Jul 2026 14:32:03 +0100
Subject: [PATCH] device-types/blk/description.tex: Add feature flag for long
 device IDs

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 device-types/blk/description.tex | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/device-types/blk/description.tex b/device-types/blk/description.tex
index 3b3a4e7..b11ae64 100644
--- a/device-types/blk/description.tex
+++ b/device-types/blk/description.tex
@@ -73,6 +73,10 @@ \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits}
     VIRTIO_BLK_REQ_FLAG_OUT_FUA flag in the \field{flags} bitfield of the
     \field{virtio_blk_req} structure for VIRTIO_BLK_T_OUT requests.
 
+\item[VIRTIO_BLK_F_LONG_ID (20)] Device returns an
+    ID of length up to 255 bytes.  See discussion of
+    VIRTIO_BLK_T_GET_ID below for how it is encoded.
+
 \end{description}
 
 \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Block Device / Feature bits / Legacy Interface: Feature bits}
@@ -516,8 +520,18 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 zeroes.
 
 VIRTIO_BLK_T_GET_ID requests fetch the device ID string from the device into
-\field{data}.  The device ID string is a NUL-padded ASCII string up to 20 bytes
-long.  If the string is 20 bytes long then there is no NUL terminator.
+\field{data}.
+
+The length and encoding depend on feature bit VIRTIO_BLK_F_LONG_ID.
+
+If the feature bit is clear, the device ID string is a NUL-padded
+ASCII string up to 20 bytes long.  If the string is 20 bytes long then
+there is no NUL terminator.
+
+If the feature bit is set, the device ID may be up to 255 bytes long
+and is returned as a NUL-padded, always NUL-terminated ASCII string
+of 256 bytes.  (The 256th byte is always NUL.)  Older drivers may
+truncate the device ID to 20 bytes.
 
 The \field{data} used for VIRTIO_BLK_T_GET_LIFETIME requests is populated
 by the device, and is of the form
@@ -911,7 +925,9 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 virtio_blk_discard_write_zeroes for VIRTIO_BLK_T_DISCARD,
 VIRTIO_BLK_T_SECURE_ERASE and VIRTIO_BLK_T_WRITE_ZEROES requests.
 
-The length of \field{data} MUST be 20 bytes for VIRTIO_BLK_T_GET_ID requests.
+The length of \field{data} MUST be 20 bytes for VIRTIO_BLK_T_GET_ID
+requests if VIRTIO_BLK_F_LONG_ID is clear, and MUST be 256 bytes if
+set.
 
 VIRTIO_BLK_T_DISCARD requests MUST NOT contain more than
 \field{max_discard_seg} struct virtio_blk_discard_write_zeroes segments in
-- 
2.55.0