code: Introduce new API level

The level will activate packet-less API for data_sink-s and (maybe) a
bit more. For now just introduce it without any real code changes.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

Author: xemul

CMakeLists.txt

@@ -70,10 +70,10 @@ option (Seastar_DEPRECATED_OSTREAM_FORMATTERS
   ON)
 
 set (Seastar_API_LEVEL
-  "8"
+  "9"
   CACHE
   STRING
-  "Seastar compatibility API level (7=unified CPU/IO scheduling groups, 8=noncopyable function in json_return_type")
+  "Seastar compatibility API level (7=unified CPU/IO scheduling groups, 8=noncopyable function in json_return_type, 9=new sink API")
 
 set_property (CACHE Seastar_API_LEVEL
   PROPERTY

configure.py

@@ -74,7 +74,7 @@ def standard_supported(standard, compiler='g++'):
                         help='Extra flags for the linker')
 arg_parser.add_argument('--optflags', action='store', dest='user_optflags', default='',
                         help='Extra optimization flags for the release mode')
-arg_parser.add_argument('--api-level', action='store', dest='api_level', default='8',
+arg_parser.add_argument('--api-level', action='store', dest='api_level', default='9',
                         help='Compatibility API level (8=latest)')
 arg_parser.add_argument('--compiler', action='store', dest='cxx', default='g++',
                         help='C++ compiler path')

doc/compatibility.md

@@ -76,6 +76,8 @@ versions of the API. For example.
      "while at it" file_impl API is forced to accept io_intent argument
    - Seastar_API_LEVEL=8 changes json_return_type to hold a noncopyable function
      and become a move-only type
+   - Seastar_API_LEVEL=9 defines the data_sink_impl::put(span<temporary_buffer>)
+     as the new and only method to be implemented
 
 Applications can use an old API_LEVEL during a transition
 period, fix their code, and move to the new API_LEVEL.
@@ -117,6 +119,7 @@ API Level History
 | 6   |  2020-09  | 2023-03 | future<T> instead of future<T...>            |
 | 7   |  2023-05  | 2024-09 | unified CPU/IO scheduling groups             |
 | 8   |  2025-08  |         | noncopyable function in json_return_type     |
+| 9   |  2025-08  |         | data_sink_impl new API                       |
 
 
 Note: The "mandatory" column indicates when backwards compatibility

include/seastar/core/internal/api-level.hh

@@ -23,7 +23,7 @@
 
 // For IDEs that don't see SEASTAR_API_LEVEL, generate a nice default
 #ifndef SEASTAR_API_LEVEL
-#define SEASTAR_API_LEVEL 8
+#define SEASTAR_API_LEVEL 9
 #endif
 
 #if SEASTAR_API_LEVEL == 8