storage: factor out config specific storage bits

This follows along the path that security::config library has taken
which is to create a dependency-free library in the subsystem that
exports the bits that are shared between the subsystem and the
configuration.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>

src/v/config/configuration.cc

@@ -21,8 +21,7 @@
 #include "security/oidc_principal_mapping.h"
 #include "security/oidc_url_parser.h"
 #include "ssx/sformat.h"
-#include "storage/chunk_cache.h"
-#include "storage/segment_appender.h"
+#include "storage/config.h"
 
 #include <chrono>
 #include <cstdint>
@@ -1170,7 +1169,7 @@ configuration::configuration()
        .example = "32768",
        .visibility = visibility::tunable},
       32_MiB,
-      storage::segment_appender::validate_fallocation_step)
+      storage::validate_fallocation_step)
   , storage_target_replay_bytes(
       *this,
       "storage_target_replay_bytes",

src/v/storage/config.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2023 Redpanda Data, Inc.
+ *
+ * Use of this software is governed by the Business Source License
+ * included in the file licenses/BSL.md
+ *
+ * As of the Change Date specified in that file, in accordance with
+ * the Business Source License, use of this software will be governed
+ * by the Apache License, Version 2.0
+ */
+#pragma once
+
+#include "base/seastarx.h"
+#include "base/units.h"
+
+#include <seastar/core/sstring.hh>
+
+#include <optional>
+
+namespace storage {
+
+inline constexpr const size_t segment_appender_fallocation_alignment = 4_KiB;
+
+/** Validator for fallocation step configuration setting */
+inline std::optional<ss::sstring>
+validate_fallocation_step(const size_t& value) {
+    if (value % segment_appender_fallocation_alignment != 0) {
+        return "Fallocation step must be multiple of 4096";
+    } else if (value < segment_appender_fallocation_alignment) {
+        return "Fallocation step must be at least 4 KiB (4096)";
+    } else if (value > 1_GiB) {
+        return "Fallocation step can't be larger than 1 GiB (1073741824)";
+    } else {
+        return std::nullopt;
+    }
+}
+
+} // namespace storage

src/v/storage/segment_appender.h

@@ -19,6 +19,7 @@
 #include "container/intrusive_list_helpers.h"
 #include "model/record.h"
 #include "ssx/semaphore.h"
+#include "storage/config.h"
 #include "storage/fwd.h"
 #include "storage/segment_appender_chunk.h"
 #include "storage/storage_resources.h"
@@ -53,7 +54,8 @@ class segment_appender {
 public:
     using chunk = segment_appender_chunk;
 
-    static constexpr const size_t fallocation_alignment = 4_KiB;
+    static constexpr const size_t fallocation_alignment
+      = segment_appender_fallocation_alignment;
     static constexpr const size_t write_behind_memory = 1_MiB;
 
     struct options {
@@ -131,20 +133,6 @@ class segment_appender {
 
     void set_callbacks(callbacks* callbacks) { _callbacks = callbacks; }
 
-    /** Validator for fallocation step configuration setting */
-    static std::optional<ss::sstring>
-    validate_fallocation_step(const size_t& value) {
-        if (value % segment_appender::fallocation_alignment != 0) {
-            return "Fallocation step must be multiple of 4096";
-        } else if (value < segment_appender::fallocation_alignment) {
-            return "Fallocation step must be at least 4 KiB (4096)";
-        } else if (value > 1_GiB) {
-            return "Fallocation step can't be larger than 1 GiB (1073741824)";
-        } else {
-            return std::nullopt;
-        }
-    }
-
     constexpr ss::io_priority_class get_priority_class() const {
         return _opts.priority;
     }