[PULL 16/18] block: Expose block limits for images in QMP

[Kevin Wolf <kwolf@redhat.com>]

This information can be useful both for debugging and for management
tools trying to configure guest devices with the optimal limits
(possibly across multiple hosts). There is no reason not to make it
available, so just add it to BlockNodeInfo.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20251024123041.51254-3-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qapi/block-core.json             | 66 ++++++++++++++++++++++++++++++++
 block/qapi.c                     | 34 ++++++++++++++--
 tests/qemu-iotests/184           |  5 ++-
 tests/qemu-iotests/184.out       |  8 ----
 tests/qemu-iotests/common.filter |  3 +-
 5 files changed, 102 insertions(+), 14 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index dc6eb4ae23..2c037183f0 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -275,6 +275,69 @@
       'file': 'ImageInfoSpecificFileWrapper'
   } }
 
+##
+# @BlockLimitsInfo:
+#
+# @request-alignment: Alignment requirement, in bytes, for
+#     offset/length of I/O requests.
+#
+# @max-discard: Maximum number of bytes that can be discarded at once.
+#     If not present, there is no specific maximum.
+#
+# @discard-alignment: Optimal alignment for discard requests in bytes.
+#     Note that this doesn't have to be a power of two.  If not
+#     present, discards don't have a alignment requirement different
+#     from @request-alignment.
+#
+# @max-write-zeroes: Maximum number of bytes that can be zeroed out at
+#     once.  If not present, there is no specific maximum.
+#
+# @write-zeroes-alignment: Optimal alignment for write zeroes requests
+#     in bytes.  Note that this doesn't have to be a power of two.  If
+#     not present, write_zeroes doesn't have a alignment requirement
+#     different from @request-alignment.
+#
+# @opt-transfer: Optimal transfer length in bytes.  If not present,
+#     there is no preferred size.
+#
+# @max-transfer: Maximal transfer length in bytes.  If not present,
+#     there is no specific maximum.
+#
+# @max-hw-transfer: Maximal hardware transfer length in bytes.
+#     Applies whenever transfers to the device bypass the kernel I/O
+#     scheduler, for example with SG_IO.  If not present, there is no
+#     specific maximum.
+#
+# @max-iov: Maximum number of scatter/gather elements
+#
+# @max-hw-iov: Maximum number of scatter/gather elements allowed by
+#     the hardware.  Applies whenever transfers to the device bypass
+#     the kernel I/O scheduler, for example with SG_IO.  If not
+#     present, the hardware limits is unknown and @max-iov is always
+#     used.
+#
+# @min-mem-alignment: Minimal required memory alignment in bytes for
+#     zero-copy I/O to succeed.  For unaligned requests, a bounce
+#     buffer will be used.
+#
+# @opt-mem-alignment: Optimal memory alignment in bytes.  This is the
+#     alignment used for any buffer allocations QEMU performs
+#     internally.
+##
+{ 'struct': 'BlockLimitsInfo',
+  'data': { 'request-alignment': 'uint32',
+            '*max-discard': 'uint64',
+            '*discard-alignment': 'uint32',
+            '*max-write-zeroes': 'uint64',
+            '*write-zeroes-alignment': 'uint32',
+            '*opt-transfer': 'uint32',
+            '*max-transfer': 'uint32',
+            '*max-hw-transfer': 'uint32',
+            'max-iov': 'int',
+            '*max-hw-iov': 'int',
+            'min-mem-alignment': 'size',
+            'opt-mem-alignment': 'size' } }
+
 ##
 # @BlockNodeInfo:
 #
@@ -304,6 +367,8 @@
 #
 # @snapshots: list of VM snapshots
 #
+# @limits: block limits that are used for I/O on the node (Since 10.2)
+#
 # @format-specific: structure supplying additional format-specific
 #     information (since 1.7)
 #
@@ -315,6 +380,7 @@
            '*cluster-size': 'int', '*encrypted': 'bool', '*compressed': 'bool',
            '*backing-filename': 'str', '*full-backing-filename': 'str',
            '*backing-filename-format': 'str', '*snapshots': ['SnapshotInfo'],
+           '*limits': 'BlockLimitsInfo',
            '*format-specific': 'ImageInfoSpecific' } }
 
 ##
diff --git a/block/qapi.c b/block/qapi.c
index 12fbf8d1b7..54521d0a68 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -235,7 +235,8 @@ int bdrv_query_snapshot_info_list(BlockDriverState *bs,
  * in @info, setting @errp on error.
  */
 static void GRAPH_RDLOCK
-bdrv_do_query_node_info(BlockDriverState *bs, BlockNodeInfo *info, Error **errp)
+bdrv_do_query_node_info(BlockDriverState *bs, BlockNodeInfo *info, bool limits,
+                        Error **errp)
 {
     int64_t size;
     const char *backing_filename;
@@ -269,6 +270,33 @@ bdrv_do_query_node_info(BlockDriverState *bs, BlockNodeInfo *info, Error **errp)
         info->dirty_flag = bdi.is_dirty;
         info->has_dirty_flag = true;
     }
+
+    if (limits) {
+        info->limits = g_new(BlockLimitsInfo, 1);
+        *info->limits = (BlockLimitsInfo) {
+            .request_alignment          = bs->bl.request_alignment,
+            .has_max_discard            = bs->bl.max_pdiscard != 0,
+            .max_discard                = bs->bl.max_pdiscard,
+            .has_discard_alignment      = bs->bl.pdiscard_alignment != 0,
+            .discard_alignment          = bs->bl.pdiscard_alignment,
+            .has_max_write_zeroes       = bs->bl.max_pwrite_zeroes != 0,
+            .max_write_zeroes           = bs->bl.max_pwrite_zeroes,
+            .has_write_zeroes_alignment = bs->bl.pwrite_zeroes_alignment != 0,
+            .write_zeroes_alignment     = bs->bl.pwrite_zeroes_alignment,
+            .has_opt_transfer           = bs->bl.opt_transfer != 0,
+            .opt_transfer               = bs->bl.opt_transfer,
+            .has_max_transfer           = bs->bl.max_transfer != 0,
+            .max_transfer               = bs->bl.max_transfer,
+            .has_max_hw_transfer        = bs->bl.max_hw_transfer != 0,
+            .max_hw_transfer            = bs->bl.max_hw_transfer,
+            .max_iov                    = bs->bl.max_iov,
+            .has_max_hw_iov             = bs->bl.max_hw_iov != 0,
+            .max_hw_iov                 = bs->bl.max_hw_iov,
+            .min_mem_alignment          = bs->bl.min_mem_alignment,
+            .opt_mem_alignment          = bs->bl.opt_mem_alignment,
+        };
+    }
+
     info->format_specific = bdrv_get_specific_info(bs, &err);
     if (err) {
         error_propagate(errp, err);
@@ -343,7 +371,7 @@ void bdrv_query_image_info(BlockDriverState *bs,
     ImageInfo *info;
 
     info = g_new0(ImageInfo, 1);
-    bdrv_do_query_node_info(bs, qapi_ImageInfo_base(info), errp);
+    bdrv_do_query_node_info(bs, qapi_ImageInfo_base(info), true, errp);
     if (*errp) {
         goto fail;
     }
@@ -397,7 +425,7 @@ void bdrv_query_block_graph_info(BlockDriverState *bs,
     BdrvChild *c;
 
     info = g_new0(BlockGraphInfo, 1);
-    bdrv_do_query_node_info(bs, qapi_BlockGraphInfo_base(info), errp);
+    bdrv_do_query_node_info(bs, qapi_BlockGraphInfo_base(info), false, errp);
     if (*errp) {
         goto fail;
     }
diff --git a/tests/qemu-iotests/184 b/tests/qemu-iotests/184
index e4cbcd8634..6d0afe9d38 100755
--- a/tests/qemu-iotests/184
+++ b/tests/qemu-iotests/184
@@ -45,8 +45,9 @@ do_run_qemu()
 
 run_qemu()
 {
-    do_run_qemu "$@" 2>&1 | _filter_testdir | _filter_qemu | _filter_qmp\
-                          | _filter_qemu_io | _filter_generated_node_ids
+    do_run_qemu "$@" 2>&1 | _filter_testdir | _filter_qemu | _filter_qmp \
+                          | _filter_qemu_io | _filter_generated_node_ids \
+                          | _filter_img_info
 }
 
 test_throttle=$($QEMU_IMG --help|grep throttle)
diff --git a/tests/qemu-iotests/184.out b/tests/qemu-iotests/184.out
index ef99bb2e9a..52692b6b3b 100644
--- a/tests/qemu-iotests/184.out
+++ b/tests/qemu-iotests/184.out
@@ -41,12 +41,6 @@ Testing:
             },
             "iops_wr": 0,
             "ro": false,
-            "children": [
-                {
-                    "node-name": "disk0",
-                    "child": "file"
-                }
-            ],
             "node-name": "throttle0",
             "backing_file_depth": 1,
             "drv": "throttle",
@@ -75,8 +69,6 @@ Testing:
             },
             "iops_wr": 0,
             "ro": false,
-            "children": [
-            ],
             "node-name": "disk0",
             "backing_file_depth": 0,
             "drv": "null-co",
diff --git a/tests/qemu-iotests/common.filter b/tests/qemu-iotests/common.filter
index 511a55b1e8..26e6b45b04 100644
--- a/tests/qemu-iotests/common.filter
+++ b/tests/qemu-iotests/common.filter
@@ -229,6 +229,7 @@ _filter_img_info()
     discard=0
     regex_json_spec_start='^ *"format-specific": \{'
     regex_json_child_start='^ *"children": \['
+    regex_json_limit_start='^ *"limits": \{'
     gsed -e "s#$REMOTE_TEST_DIR#TEST_DIR#g" \
         -e "s#$IMGPROTO:$TEST_DIR#TEST_DIR#g" \
         -e "s#$TEST_DIR#TEST_DIR#g" \
@@ -261,7 +262,7 @@ _filter_img_info()
                 discard=1
             elif [[ $line =~ "Child node '/" ]]; then
                 discard=1
-            elif [[ $line =~ $regex_json_spec_start ]]; then
+            elif [[ $line =~ $regex_json_spec_start || $line =~ $regex_json_limit_start ]]; then
                 discard=2
                 regex_json_end="^${line%%[^ ]*}\\},? *$"
             elif [[ $line =~ $regex_json_child_start ]]; then
-- 
2.51.0