[PATCH] virtio-blk: add secure discard feature to specification

[yadong.qi@intel.com]

From: Yadong Qi <yadong.qi@intel.com>

There are user requests to use BLKSECDISCARD on virtio-blk device.
Hence in this proposal, extend virtio-blk protocol to support secure
discard command.

Introduced new feature flag and command type:
    VIRTIO_BLK_F_SECDISCARD
    VIRTIO_BLK_T_SECDISCARD

This feature is a passthrough feature on backend because it is hard
to emulate a secure discard. So virtio-blk will report this feature
to guest OS if backend device support such kind of feature. And
when guest OS issues a secure discard command, backend driver will
passthrough the command to host device blocks.

Signed-off-by: Yadong Qi <yadong.qi@intel.com>
---
 content.tex | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/content.tex b/content.tex
index 5d112af..305c51f 100644
--- a/content.tex
+++ b/content.tex
@@ -4435,6 +4435,13 @@ \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits}
 
 \item[VIRTIO_BLK_F_LIFETIME (15)] Device supports providing storage lifetime
      information.
+
+\item[VIRTIO_BLK_F_SECDISCARD (16)] Device can support secure discard command,
+    share the same maximum discard sectors size and discard segment number with
+    VIRTIO_BLK_F_DISCARD. Maximum discard sectors size in
+    \field{max_discard_sectors} and maximum discard segment number in
+    \field{max_discard_seg}.
+
 \end{description}
 
 \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Block Device / Feature bits / Legacy Interface: Feature bits}
@@ -4619,7 +4626,8 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 The type of the request is either a read (VIRTIO_BLK_T_IN), a write
 (VIRTIO_BLK_T_OUT), a discard (VIRTIO_BLK_T_DISCARD), a write zeroes
 (VIRTIO_BLK_T_WRITE_ZEROES), a flush (VIRTIO_BLK_T_FLUSH), a get device ID
-string command (VIRTIO_BLK_T_GET_ID), or a get device lifetime command
+string command (VIRTIO_BLK_T_GET_ID), a secure discard
+(VIRTIO_BLK_T_SECDISCARD), or a get device lifetime command
 (VIRTIO_BLK_T_GET_LIFETIME).
 
 \begin{lstlisting}
@@ -4630,6 +4638,7 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 #define VIRTIO_BLK_T_GET_LIFETIME 10
 #define VIRTIO_BLK_T_DISCARD      11
 #define VIRTIO_BLK_T_WRITE_ZEROES 13
+#define VIRTIO_BLK_T_SECDISCARD   14
 \end{lstlisting}
 
 The \field{sector} number indicates the offset (multiplied by 512) where
@@ -4729,13 +4738,13 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 and VIRTIO_BLK_T_OUT requests.
 
 The length of \field{data} MUST be a multiple of the size of struct
-virtio_blk_discard_write_zeroes for VIRTIO_BLK_T_DISCARD and
-VIRTIO_BLK_T_WRITE_ZEROES requests.
+virtio_blk_discard_write_zeroes for VIRTIO_BLK_T_DISCARD,
+VIRTIO_BLK_T_SECDISCARD and VIRTIO_BLK_T_WRITE_ZEROES requests.
 
 The length of \field{data} MUST be 20 bytes for VIRTIO_BLK_T_GET_ID requests.
 
-VIRTIO_BLK_T_DISCARD requests MUST NOT contain more than
-\field{max_discard_seg} struct virtio_blk_discard_write_zeroes segments in
+VIRTIO_BLK_T_DISCARD and VIRTIO_BLK_T_SECDISCARD requests MUST NOT contain more
+than \field{max_discard_seg} struct virtio_blk_discard_write_zeroes segments in
 \field{data}.
 
 VIRTIO_BLK_T_WRITE_ZEROES requests MUST NOT contain more than
@@ -4764,7 +4773,7 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
 write any data.
 
 The device MUST set the \field{status} byte to VIRTIO_BLK_S_UNSUPP for
-discard and write zeroes commands if any unknown flag is set.
+discard, secure discard and write zeroes commands if any unknown flag is set.
 Furthermore, the device MUST set the \field{status} byte to
 VIRTIO_BLK_S_UNSUPP for discard commands if the \field{unmap} flag is set.
 
-- 
2.25.1