[PATCH v2 14/15] RFC: nbd/client: Accept 64-bit hole chunks

[Eric Blake <eblake@redhat.com>]

As part of adding extended headers, the NBD spec debated about adding
support for reading 64-bit holes.  It was documented in a separate
upstream commit XXX[*] to make it easier to decide whether 64-bit
holes should be required of all clients supporting extended headers,
or whether it is an unneeded feature; hence, the qemu work to support
it is also pulled out into a separate commit.

Note that we can also tolerate a non-compliant server sending the new
chunk even when it should not.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
[*] Fix commit id if we actually go with idea
---
 include/block/nbd.h |  8 ++++++++
 block/nbd.c         | 26 ++++++++++++++++++++------
 nbd/common.c        |  4 +++-
 3 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/include/block/nbd.h b/include/block/nbd.h
index 2a65c606c9..18b6bad038 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -133,6 +133,13 @@ typedef struct NBDStructuredReadHole {
     uint32_t length;
 } QEMU_PACKED NBDStructuredReadHole;

+/* Complete chunk for NBD_REPLY_TYPE_OFFSET_HOLE_EXT */
+typedef struct NBDStructuredReadHoleExt {
+    /* header's length == 16 */
+    uint64_t offset;
+    uint64_t length;
+} QEMU_PACKED NBDStructuredReadHoleExt;
+
 /* Header of all NBD_REPLY_TYPE_ERROR* errors */
 typedef struct NBDStructuredError {
     /* header's length >= 6 */
@@ -309,6 +316,7 @@ enum {
 #define NBD_REPLY_TYPE_NONE              0
 #define NBD_REPLY_TYPE_OFFSET_DATA       1
 #define NBD_REPLY_TYPE_OFFSET_HOLE       2
+#define NBD_REPLY_TYPE_OFFSET_HOLE_EXT   3
 #define NBD_REPLY_TYPE_BLOCK_STATUS      5
 #define NBD_REPLY_TYPE_BLOCK_STATUS_EXT  6
 #define NBD_REPLY_TYPE_ERROR             NBD_REPLY_ERR(1)
diff --git a/block/nbd.c b/block/nbd.c
index 44ab5437ea..968d5d8a37 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -570,20 +570,26 @@ static inline uint64_t payload_advance64(uint8_t **payload)

 static int nbd_parse_offset_hole_payload(BDRVNBDState *s,
                                          NBDStructuredReplyChunk *chunk,
-                                         uint8_t *payload, uint64_t orig_offset,
+                                         uint8_t *payload, bool wide,
+                                         uint64_t orig_offset,
                                          QEMUIOVector *qiov, Error **errp)
 {
     uint64_t offset;
-    uint32_t hole_size;
+    uint64_t hole_size;
+    size_t len = wide ? sizeof(hole_size) : sizeof(uint32_t);

-    if (chunk->length != sizeof(offset) + sizeof(hole_size)) {
+    if (chunk->length != sizeof(offset) + len) {
         error_setg(errp, "Protocol error: invalid payload for "
                          "NBD_REPLY_TYPE_OFFSET_HOLE");
         return -EINVAL;
     }

     offset = payload_advance64(&payload);
-    hole_size = payload_advance32(&payload);
+    if (wide) {
+        hole_size = payload_advance64(&payload);
+    } else {
+        hole_size = payload_advance32(&payload);
+    }

     if (!hole_size || offset < orig_offset || hole_size > qiov->size ||
         offset > orig_offset + qiov->size - hole_size) {
@@ -596,6 +602,7 @@ static int nbd_parse_offset_hole_payload(BDRVNBDState *s,
         trace_nbd_structured_read_compliance("hole");
     }

+    assert(hole_size <= SIZE_MAX);
     qemu_iovec_memset(qiov, offset - orig_offset, 0, hole_size);

     return 0;
@@ -1094,9 +1101,16 @@ static int coroutine_fn nbd_co_receive_cmdread_reply(BDRVNBDState *s, uint64_t h
              * in qiov
              */
             break;
+        case NBD_REPLY_TYPE_OFFSET_HOLE_EXT:
+            if (!s->info.extended_headers) {
+                trace_nbd_extended_headers_compliance("hole_ext");
+            }
+            /* fallthrough */
         case NBD_REPLY_TYPE_OFFSET_HOLE:
-            ret = nbd_parse_offset_hole_payload(s, &reply.structured, payload,
-                                                offset, qiov, &local_err);
+            ret = nbd_parse_offset_hole_payload(
+                s, &reply.structured, payload,
+                chunk->type == NBD_REPLY_TYPE_OFFSET_HOLE_EXT,
+                offset, qiov, &local_err);
             if (ret < 0) {
                 nbd_channel_error(s, ret);
                 nbd_iter_channel_error(&iter, ret, &local_err);
diff --git a/nbd/common.c b/nbd/common.c
index 137466defd..54f7d6a4fd 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -174,7 +174,9 @@ const char *nbd_reply_type_lookup(uint16_t type)
     case NBD_REPLY_TYPE_OFFSET_DATA:
         return "data";
     case NBD_REPLY_TYPE_OFFSET_HOLE:
-        return "hole";
+        return "hole (32-bit)";
+    case NBD_REPLY_TYPE_OFFSET_HOLE_EXT:
+        return "hole (64-bit)";
     case NBD_REPLY_TYPE_BLOCK_STATUS:
         return "block status (32-bit)";
     case NBD_REPLY_TYPE_BLOCK_STATUS_EXT:
-- 
2.38.1