[v3,2/6] nbd: Add 'qemu-nbd -A' to expose allocation depth

diff --git a/docs/tools/qemu-nbd.rst b/docs/tools/qemu-nbd.rst
index 667861cb22e9..0e545a97cfa3 100644
--- a/docs/tools/qemu-nbd.rst
+++ b/docs/tools/qemu-nbd.rst
@@ -72,6 +72,12 @@  driver options if ``--image-opts`` is specified.

   Export the disk as read-only.

+.. option:: -A, --allocation-depth
+
+  Expose allocation depth information via the
+  ``qemu:allocation-depth`` context accessible through
+  NBD_OPT_SET_META_CONTEXT.
+
 .. option:: -B, --bitmap=NAME

   If *filename* has a qcow2 persistent bitmap *NAME*, expose
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 3758ea991269..249bd434f4eb 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3882,9 +3882,12 @@ 
 #
 # @tls-creds: TLS credentials ID
 #
-# @x-dirty-bitmap: A "qemu:dirty-bitmap:NAME" string to query in place of
+# @x-dirty-bitmap: A metacontext name such as "qemu:dirty-bitmap:NAME" or
+#                  "qemu:allocation-depth" to query in place of the
 #                  traditional "base:allocation" block status (see
-#                  NBD_OPT_LIST_META_CONTEXT in the NBD protocol) (since 3.0)
+#                  NBD_OPT_LIST_META_CONTEXT in the NBD protocol; and
+#                  yes, naming this option x-context would have made
+#                  more sense) (since 3.0)
 #
 # @reconnect-delay: On an unexpected disconnect, the nbd client tries to
 #                   connect again until succeeding or encountering a serious
diff --git a/qapi/block-export.json b/qapi/block-export.json
index 65804834d905..524cd3a94400 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -78,11 +78,15 @@ 
 #          NBD client can use NBD_OPT_SET_META_CONTEXT with
 #          "qemu:dirty-bitmap:NAME" to inspect the bitmap. (since 4.0)
 #
+# @alloc: Also export the allocation map for @device, so the NBD client
+#         can use NBD_OPT_SET_META_CONTEXT with "qemu:allocation-depth"
+#         to inspect allocation details. (since 5.2)
+#
 # Since: 5.0
 ##
 { 'struct': 'BlockExportOptionsNbd',
   'data': { '*name': 'str', '*description': 'str',
-            '*bitmap': 'str' } }
+            '*bitmap': 'str', '*alloc': 'bool' } }

 ##
 # @NbdServerAddOptions:
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 8174023e5c47..f9012f93e2bb 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -212,6 +212,8 @@  void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
             .description        = g_strdup(arg->description),
             .has_bitmap         = arg->has_bitmap,
             .bitmap             = g_strdup(arg->bitmap),
+            .has_alloc          = arg->alloc,
+            .alloc              = arg->alloc,
         },
     };

diff --git a/nbd/server.c b/nbd/server.c
index 59533090f5ce..e24495d93e2e 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1597,6 +1597,8 @@  static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
         assert(strlen(exp->export_bitmap_context) < NBD_MAX_STRING_SIZE);
     }

+    exp->alloc_context = arg->alloc;
+
     blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);

     QTAILQ_INSERT_TAIL(&exports, exp, next);
diff --git a/qemu-nbd.c b/qemu-nbd.c
index c731dda04ec0..e3cff17d6760 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -99,6 +99,7 @@  static void usage(const char *name)
 "\n"
 "Exposing part of the image:\n"
 "  -o, --offset=OFFSET       offset into the image\n"
+"  -A, --allocation-depth    expose the allocation depth\n"
 "  -B, --bitmap=NAME         expose a persistent dirty bitmap\n"
 "\n"
 "General purpose options:\n"
@@ -519,7 +520,7 @@  int main(int argc, char **argv)
     char *device = NULL;
     QemuOpts *sn_opts = NULL;
     const char *sn_id_or_name = NULL;
-    const char *sopt = "hVb:o:p:rsnc:dvk:e:f:tl:x:T:D:B:L";
+    const char *sopt = "hVb:o:p:rsnc:dvk:e:f:tl:x:T:D:AB:L";
     struct option lopt[] = {
         { "help", no_argument, NULL, 'h' },
         { "version", no_argument, NULL, 'V' },
@@ -528,6 +529,7 @@  int main(int argc, char **argv)
         { "socket", required_argument, NULL, 'k' },
         { "offset", required_argument, NULL, 'o' },
         { "read-only", no_argument, NULL, 'r' },
+        { "allocation-depth", no_argument, NULL, 'A' },
         { "bitmap", required_argument, NULL, 'B' },
         { "connect", required_argument, NULL, 'c' },
         { "disconnect", no_argument, NULL, 'd' },
@@ -569,6 +571,7 @@  int main(int argc, char **argv)
     QDict *options = NULL;
     const char *export_name = NULL; /* defaults to "" later for server mode */
     const char *export_description = NULL;
+    bool alloc_depth = false;
     const char *bitmap = NULL;
     const char *tlscredsid = NULL;
     bool imageOpts = false;
@@ -694,6 +697,9 @@  int main(int argc, char **argv)
             readonly = true;
             flags &= ~BDRV_O_RDWR;
             break;
+        case 'A':
+            alloc_depth = true;
+            break;
         case 'B':
             bitmap = optarg;
             break;
@@ -791,8 +797,8 @@  int main(int argc, char **argv)
             exit(EXIT_FAILURE);
         }
         if (export_name || export_description || dev_offset ||
-            device || disconnect || fmt || sn_id_or_name || bitmap ||
-            seen_aio || seen_discard || seen_cache) {
+            device || disconnect || fmt || sn_id_or_name || alloc_depth ||
+            bitmap || seen_aio || seen_discard || seen_cache) {
             error_report("List mode is incompatible with per-device settings");
             exit(EXIT_FAILURE);
         }
@@ -1078,6 +1084,8 @@  int main(int argc, char **argv)
             .description        = g_strdup(export_description),
             .has_bitmap         = !!bitmap,
             .bitmap             = g_strdup(bitmap),
+            .has_alloc          = alloc_depth,
+            .alloc              = alloc_depth,
         },
     };
     blk_exp_add(export_opts, &error_fatal);
diff --git a/tests/qemu-iotests/309 b/tests/qemu-iotests/309
new file mode 100755
index 000000000000..b6734794bb68
--- /dev/null
+++ b/tests/qemu-iotests/309
@@ -0,0 +1,73 @@ 
+#!/usr/bin/env bash
+#
+# Test qemu-nbd -A
+#
+# Copyright (C) 2018-2020 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+seq="$(basename $0)"
+echo "QA output created by $seq"
+
+status=1 # failure is the default!
+
+_cleanup()
+{
+    _cleanup_test_img
+    nbd_server_stop
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+. ./common.nbd
+
+_supported_fmt qcow2
+_supported_proto file
+_supported_os Linux
+_require_command QEMU_NBD
+
+echo
+echo "=== Initial image setup ==="
+echo
+
+TEST_IMG="$TEST_IMG.base" _make_test_img 4M
+$QEMU_IO -c 'w 0 2M' -f $IMGFMT "$TEST_IMG.base" | _filter_qemu_io
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 4M
+$QEMU_IO -c 'w 1M 2M' -f $IMGFMT "$TEST_IMG" | _filter_qemu_io
+
+echo
+echo "=== Check allocation over NBD ==="
+echo
+
+$QEMU_IMG map --output=json -f qcow2 "$TEST_IMG"
+IMG="driver=nbd,server.type=unix,server.path=$nbd_unix_socket"
+nbd_server_start_unix_socket -r -f qcow2 -A "$TEST_IMG"
+# Normal -f raw NBD block status loses access to allocation information
+$QEMU_IMG map --output=json --image-opts \
+    "$IMG" | _filter_qemu_img_map
+# But since we used -A, and use x-dirty-bitmap as a hack for reading bitmaps,
+# we can reconstruct it, by abusing block status to report:
+#    NBD_STATE_DEPTH_UNALLOC => "zero":false, "data":true
+#    NBD_STATE_DEPTH_LOCAL   => "zero":false, "data":false
+#    NBD_STATE_DEPTH_BACKING => "zero":true,  "data":true
+$QEMU_IMG map --output=json --image-opts \
+    "$IMG,x-dirty-bitmap=qemu:allocation-depth" | _filter_qemu_img_map
+
+# success, all done
+echo '*** done'
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/309.out b/tests/qemu-iotests/309.out
new file mode 100644
index 000000000000..db75bb6b0df9
--- /dev/null
+++ b/tests/qemu-iotests/309.out
@@ -0,0 +1,22 @@ 
+QA output created by 309
+
+=== Initial image setup ===
+
+Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=4194304
+wrote 2097152/2097152 bytes at offset 0
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4194304 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+wrote 2097152/2097152 bytes at offset 1048576
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+=== Check allocation over NBD ===
+
+[{ "start": 0, "length": 1048576, "depth": 1, "zero": false, "data": true, "offset": 327680},
+{ "start": 1048576, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": 327680},
+{ "start": 3145728, "length": 1048576, "depth": 1, "zero": true, "data": false}]
+[{ "start": 0, "length": 3145728, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 3145728, "length": 1048576, "depth": 0, "zero": true, "data": false, "offset": OFFSET}]
+[{ "start": 0, "length": 1048576, "depth": 0, "zero": true, "data": true, "offset": OFFSET},
+{ "start": 1048576, "length": 2097152, "depth": 0, "zero": false, "data": false},
+{ "start": 3145728, "length": 1048576, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+*** done
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index 9e4f7c01530d..a567fa97d7e5 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -315,3 +315,4 @@ 
 304 rw quick
 305 rw quick
 307 rw quick export
+309 rw auto quick