LogManager: implement system module, client api, logging api (#1617)

Some notes:

* Unless `atmosphere!enable_log_manager` is true, Nintendo's log manager will be used instead.
  * This prevents paying memory costs for LM when not enabling logging.
  * To facilitate this, Atmosphere's log manager has a different program id from Nintendo's.
  * `atmosphere!enable_htc` implies `atmosphere!enable_log_manager`.
* LogManager logs to tma, and the SD card (if `lm!enable_sd_card_logging` is true, which it is by default).
* Binary logs are saved to `lm!sd_card_log_output_directory`, which is `atmosphere/binlogs` by default.

libraries/libstratosphere/source/lm/srv/lm_log_buffer.hpp

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::lm::srv {
+
+    class LogBuffer {
+        NON_COPYABLE(LogBuffer);
+        NON_MOVEABLE(LogBuffer);
+        private:
+            struct BufferInfo {
+                u8 *m_head;
+                size_t m_stored_size;
+                size_t m_reference_count;
+            };
+        public:
+            using FlushFunction = bool (*)(const u8 *data, size_t size);
+        private:
+            BufferInfo m_buffers[2];
+            BufferInfo *m_push_buffer;
+            BufferInfo *m_flush_buffer;
+            size_t m_buffer_size;
+            FlushFunction m_flush_function;
+            os::SdkMutex m_push_buffer_mutex;
+            os::SdkMutex m_flush_buffer_mutex;
+            os::SdkConditionVariable m_cv_push_ready;
+            os::SdkConditionVariable m_cv_flush_ready;
+            bool m_push_canceled;
+            size_t m_push_ready_wait_count;
+        public:
+            constexpr explicit LogBuffer(void *buffer, size_t buffer_size, FlushFunction f)
+                : m_buffers{}, m_push_buffer(m_buffers + 0), m_flush_buffer(m_buffers + 1),
+                  m_buffer_size(buffer_size / 2), m_flush_function(f), m_push_buffer_mutex{},
+                  m_flush_buffer_mutex{}, m_cv_push_ready{}, m_cv_flush_ready{},
+                  m_push_canceled(false), m_push_ready_wait_count(0)
+            {
+                AMS_ASSERT(buffer != nullptr);
+                AMS_ASSERT(buffer_size > 0);
+                AMS_ASSERT(f != nullptr);
+
+                m_buffers[0].m_head = static_cast<u8 *>(buffer);
+                m_buffers[1].m_head = static_cast<u8 *>(buffer) + (buffer_size / 2);
+            }
+
+            static LogBuffer &GetDefaultInstance();
+
+            bool Push(const void *data, size_t size) { return this->PushImpl(data, size, true); }
+            bool TryPush(const void *data, size_t size) { return this->PushImpl(data, size, false); }
+
+            void CancelPush();
+
+            bool Flush() { return this->FlushImpl(true); }
+            bool TryFlush() { return this->FlushImpl(false); }
+        private:
+            bool PushImpl(const void *data, size_t size, bool blocking);
+            bool FlushImpl(bool blocking);
+    };
+
+}