[Qemu-devel] [PATCH] virtio-spec: document block CMD and FLUSH

[Michael S. Tsirkin]

I took a stub at documenting CMD and FLUSH request types in virtio
block.  Christoph, could you look over this please?

I note that the interface seems full of warts to me,
this might be a first step to cleaning them.

One issue I struggled with especially is how type
field mixes bits and non-bit values. I ended up
simply defining all legal values, so that we have
CMD = 2, CMD_OUT = 3 and so on.

I also avoided instroducing inhdr/outhdr structures
that virtio blk driver in linux uses, I was concerned
that nesting tables will confuse the reader.

Comments welcome.

Signed-off-by: Michael S. Tsirkin <address@hidden>

--

diff --git a/virtio-spec.lyx b/virtio-spec.lyx
index d16104a..ed35893 100644
--- a/virtio-spec.lyx
+++ b/virtio-spec.lyx
@@ -67,7 +67,11 @@ IBM Corporation
 \end_layout
 
 \begin_layout Standard
+
+\change_deleted 0 1266531118
 FIXME: virtio block scsi passthrough section
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
@@ -4376,7 +4380,7 @@ struct virtio_net_ctrl_mac {
 The device can filter incoming packets by any number of destination MAC
  addresses.
 \begin_inset Foot
-status open
+status collapsed
 
 \begin_layout Plain Layout
 Since there are no guarentees, it can use a hash filter orsilently switch
@@ -4549,6 +4553,22 @@ blk_size
 \end_inset
 
 .
+\change_inserted 0 1266444580
+
+\end_layout
+
+\begin_layout Description
+
+\change_inserted 0 1266471229
+VIRTIO_BLK_F_SCSI (7) Device supports scsi packet commands.
+\end_layout
+
+\begin_layout Description
+
+\change_inserted 0 1266444605
+VIRTIO_BLK_F_FLUSH (9) Cache flush command support.
+\change_unchanged
+
 \end_layout
 
 \begin_layout Description
@@ -4700,17 +4720,25 @@ struct virtio_blk_req {
 
 \begin_layout Plain Layout
 
+\change_deleted 0 1266472188
+
 #define VIRTIO_BLK_T_IN          0
 \end_layout
 
 \begin_layout Plain Layout
 
+\change_deleted 0 1266472188
+
 #define VIRTIO_BLK_T_OUT         1
 \end_layout
 
 \begin_layout Plain Layout
 
+\change_deleted 0 1266472188
+
 #define VIRTIO_BLK_T_BARRIER    0x80000000
+\change_unchanged
+
 \end_layout
 
 \begin_layout Plain Layout
@@ -4735,11 +4763,15 @@ struct virtio_blk_req {
 
 \begin_layout Plain Layout
 
+\change_deleted 0 1266472204
+
 #define VIRTIO_BLK_S_OK        0
 \end_layout
 
 \begin_layout Plain Layout
 
+\change_deleted 0 1266472204
+
 #define VIRTIO_BLK_S_IOERR     1
 \end_layout
 
@@ -4759,32 +4791,481 @@ struct virtio_blk_req {
 \end_layout
 
 \begin_layout Standard
-The type of the request is either a read (VIRTIO_BLK_T_IN) or a write 
(VIRTIO_BL
-K_T_OUT); the high bit indicates that this request acts as a barrier and
- that all preceeding requests must be complete before this one, and all
- following requests must not be started until this is complete.
+
+\change_inserted 0 1266472490
+If the device has VIRTIO_BLK_F_SCSI feature, it can also support scsi packet
+ command requests, each of these requests is of form:
+\begin_inset listings
+inline false
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472395
+
+struct virtio_scsi_pc_req {
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472375
+
+       u32 type;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472375
+
+       u32 ioprio;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266474298
+
+       u64 sector;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266474308
+
+    char cmd[];
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266505809
+
+       char data[][512];
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266505825
+
+#define SCSI_SENSE_BUFFERSIZE   96
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266505848
+
+    u8 sense[SCSI_SENSE_BUFFERSIZE];
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472969
+
+    u32 errors;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472979
+
+    u32 data_len;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472984
+
+    u32 sense_len;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472987
+
+    u32 residual;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472375
+
+       u8 status;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472375
+
+};
+\end_layout
+
+\end_inset
+
+
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
-The ioprio field is a hint about the relative priorities of requests to
- the device: higher numbers indicate more important requests.
+The 
+\emph on
+type
+\emph default
+ of the request is either a read (VIRTIO_BLK_T_IN)
+\change_inserted 0 1266495815
+,
+\change_unchanged
+ 
+\change_deleted 0 1266495817
+or
+\change_unchanged
+ a write (VIRTIO_BLK_T_OUT)
+\change_inserted 0 1266497316
+, a scsi packet command (VIRTIO_BLK_T_SCSI_CMD or VIRTIO_BLK_T_SCSI_CMD_OUT
+\begin_inset Foot
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266497390
+the SCSI_CMD and SCSI_CMD_OUT types are equivalent, the device does not
+ distinguish between them
+\change_unchanged
+
+\end_layout
+
+\end_inset
+
+) or a flush (VIRTIO_BLK_T_FLUSH or VIRTIO_BLK_T_FLUSH_OUT
+\begin_inset Foot
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266497402
+the FLUSH and FLUSH_OUT types are equivalent, the device does not distinguish
+ between them
+\change_unchanged
+
+\end_layout
+
+\end_inset
+
+)
+\change_deleted 0 1266503753
+;
+\change_inserted 0 1266503758
+.
+
+\change_unchanged
+ 
+\change_inserted 0 1266497301
+If the device has VIRTIO_BLK_F_BARRIER feature
+\begin_inset space ~
+\end_inset
+
+
+\change_unchanged
+the high bit
+\change_inserted 0 1266497301
+ (VIRTIO_BLK_T_BARRIER)
+\change_unchanged
+ indicates that this request acts as a barrier and that all preceeding requests
+ must be complete before this one, and all following requests must not be
+ started until this is complete.
+
+\change_inserted 0 1266504385
+ Note that a barrier does not flush caches in the underlying backend device
+ in host, and thus does not serve as data consistency guarantee.
+ Driver must use FLUSH request to flush the host cache.
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
-The sector number indicates the offset (multiplied by 512) where the read
- or write is to occur.
+
+\change_inserted 0 1266472135
+\begin_inset listings
+inline false
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266495783
+
+#define VIRTIO_BLK_T_IN           0
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266495782
+
+#define VIRTIO_BLK_T_OUT          1
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266495781
+
+#define VIRTIO_BLK_T_SCSI_CMD     2
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266495799
+
+#define VIRTIO_BLK_T_SCSI_CMD_OUT 3
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266497225
+
+#define VIRTIO_BLK_T_FLUSH        4
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266497237
+
+#define VIRTIO_BLK_T_FLUSH_OUT    5
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266472135
+
+#define VIRTIO_BLK_T_BARRIER    0x80000000
+\end_layout
+
+\end_inset
+
+
 \end_layout
 
 \begin_layout Standard
-Note that these first three fields are always read-only: the data field
- is either read-only or write-only, depending on the type of the request.
+The 
+\emph on
+ioprio
+\emph default
+ field is a hint about the relative priorities of requests to the device:
+ higher numbers indicate more important requests.
+\end_layout
+
+\begin_layout Standard
+The 
+\emph on
+sector
+\emph default
+ number indicates the offset (multiplied by 512) where the read or write
+ is to occur.
+
+\change_inserted 0 1266504683
+ This field is unused and set to 0 for scsi packet commands and for flush
+ commands.
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1266527996
+The 
+\emph on
+cmd
+\emph default
+ field is only present for scsi packet command requests, and indicates the
+ command to perform.
+ This field must reside in a single, separate read-only buffer; command
+ length can be derived from the length of this buffer.
+ 
+\change_unchanged
+
+\end_layout
+
+\begin_layout Standard
+Note that these first three
+\change_inserted 0 1266504407
+ (four for scsi packet commands)
+\change_unchanged
+ fields are always read-only: the 
+\emph on
+data
+\emph default
+ field is either read-only or write-only, depending on 
+\change_deleted 0 1266505122
+the type of
+\change_unchanged
+ the request.
  The size of the read or write can be derived from the total size of the
- request buffer.
+ request buffer
+\change_inserted 0 1266504916
+s
+\change_unchanged
+.
+\change_inserted 0 1266506030
+
 \end_layout
 
 \begin_layout Standard
-The final byte is written by the device: either VIRTIO_BLK_S_OK or 
VIRTIO_BLK_S_
-IOERR.
+
+\change_inserted 0 1266528308
+The
+\emph on
+ sense
+\emph default
+ field is only present for scsi packet command requests, and indicates the
+ buffer for scsi sense data.
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1266528658
+The 
+\emph on
+data_len
+\emph default
+ field is only present for scsi packet command requests, this field is 
deprecate
+d, and should be ignored by the driver.
+ Historically, devices copied data length there.
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1266528675
+The 
+\emph on
+sense_len
+\emph default
+ field is only present for scsi packet command requests and indicates the
+ number of bytes actually written to the 
+\emph on
+sense
+\emph default
+ buffer.
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1266528717
+The 
+\emph on
+residual
+\emph default
+ field is only present for scsi packet command requests and indicates the
+ residual size, calculated as data length - number of bytes actually 
transferred.
+\change_unchanged
+
+\end_layout
+
+\begin_layout Standard
+The final 
+\change_inserted 0 1266471813
+
+\emph on
+status
+\emph default
+ 
+\change_unchanged
+byte is written by the device: either VIRTIO_BLK_S_OK
+\change_inserted 0 1266528888
+ for success,
+\change_deleted 0 1266528889
+ or
+\change_unchanged
+ VIRTIO_BLK_S_IOERR
+\change_inserted 0 1266529171
+ for host or guest error or VIRTIO_BLK_S_UNSUPP for a request unsupported
+ by host:
+\change_deleted 0 1266471769
+.
+\change_inserted 0 1266471782
+
+\begin_inset listings
+inline false
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266471782
+
+#define VIRTIO_BLK_S_OK        0
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266528846
+
+#define VIRTIO_BLK_S_IOERR     1
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 0 1266528863
+
+#define VIRTIO_BLK_S_UNSUPP    2
+\change_unchanged
+
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1266528247
+Historically, devices assumed that the fields 
+\emph on
+type
+\emph default
+, 
+\emph on
+ioprio
+\emph default
+ and 
+\emph on
+sector
+\emph default
+ reside in a single, separate read-only buffer; the fields 
+\emph on
+errors
+\emph default
+, 
+\emph on
+data_len
+\emph default
+, 
+\emph on
+sense_len
+\emph default
+ and 
+\emph on
+residual
+\emph default
+ reside in a single, separate write-only buffer; the 
+\emph on
+sense
+\emph default
+ field in a separate write-only buffer of size 96 bytes, by itself; the
+ fields 
+\emph on
+errors
+\emph default
+, 
+\emph on
+data_len
+\emph default
+, 
+\emph on
+sense_len
+\emph default
+ and 
+\emph on
+residual
+\emph default
+ in a single write-only buffer; and the 
+\emph on
+status
+\emph default
+ field is a separate read-only buffer of size 1 byte, by itself.
 \end_layout
 
 \begin_layout Chapter*