[kernel] Move log buffer to its own memory section

In prep for the coming change to keep log entries as a true ring buffer,
move the log buffer from bss into its own memory section.

Related changes in this commit:
- New vm_area_ring, which maps a set of pages twice to allow easy linear
  reading of data from a ring buffer when it wraps around the end.
- logger_init() went away, and the logger ctor is called from
  mem::initialize()
- Instead of an event object, the logger just has a bare wait_queue
- util::counted::from template type changed slightly to allow easy
  conversion from an intptr_t as well as a pointer
- Previously added debugcon_logger code removed - this will be added in
  a separate file in a followup commit

src/kernel/kernel_main.cpp

@@ -36,9 +36,8 @@ kernel_main(bootproto::args *args)
         panic::install(args->panic_handler, args->symbol_table);
     }
 
-    logger_init();
-
     cpu_data *cpu = bsp_early_init();
+    mem::initialize(*args);
 
     kassert(args->magic == bootproto::args_magic,
             "Bad kernel args magic number");
@@ -51,7 +50,6 @@ kernel_main(bootproto::args *args)
 
     disable_legacy_pic();
 
-    mem::initialize(*args);
 
     bsp_late_init();
 

src/kernel/logger.cpp

@@ -6,15 +6,9 @@
 
 #include "assert.h"
 #include "logger.h"
-#include "memory.h"
 #include "objects/system.h"
 #include "objects/thread.h"
 
-static constexpr bool j6_debugcon_enable = false;
-static constexpr uint16_t j6_debugcon_port = 0x6600;
-
-static uint8_t log_buffer[log::logger::log_pages * arch::frame_size];
-
 // The logger is initialized _before_ global constructors are called,
 // so that we can start log output immediately. Keep its constructor
 // from being called here so as to not overwrite the previous initialization.
@@ -25,36 +19,16 @@ log::logger &g_logger = __g_logger_storage.value;
 namespace log {
 
 logger *logger::s_log = nullptr;
-const char *logger::s_level_names[] = {"", "fatal", "error", "warn", "info", "verbose", "spam"};
-const char *logger::s_area_names[] = {
-#define LOG(name, lvl) #name ,
-#include <j6/tables/log_areas.inc>
-#undef LOG
-    nullptr
-};
-
-inline void
-debug_out(const char *msg, size_t size)
-{
-    asm ( "rep outsb;" :: "c"(size), "d"(j6_debugcon_port), "S"(msg) );
-}
-
-inline void
-debug_newline()
-{
-    static const char *newline = "\r\n";
-    asm ( "rep outsb;" :: "c"(2), "d"(j6_debugcon_port), "S"(newline) );
-}
 
 logger::logger() :
-    m_buffer(nullptr, 0)
+    m_buffer {nullptr, 0}
 {
     memset(&m_levels, 0, sizeof(m_levels));
     s_log = this;
 }
 
-logger::logger(uint8_t *buffer, size_t size) :
-    m_buffer(buffer, size)
+logger::logger(util::buffer data) :
+    m_buffer {data.pointer, data.count}
 {
     memset(&m_levels, 0, sizeof(m_levels));
     s_log = this;
@@ -70,13 +44,6 @@ logger::output(level severity, logs area, const char *fmt, va_list args)
 {
     char buffer[256];
 
-    if constexpr (j6_debugcon_enable) {
-        size_t dlen = util::format({buffer, sizeof(buffer)}, "%7s %7s| ",
-                s_area_names[static_cast<uint8_t>(area)],
-                s_level_names[static_cast<uint8_t>(severity)]);
-        debug_out(buffer, dlen);
-    }
-
     entry *header = reinterpret_cast<entry *>(buffer);
     header->bytes = sizeof(entry);
     header->area = area;
@@ -86,11 +53,6 @@ logger::output(level severity, logs area, const char *fmt, va_list args)
     header->message[mlen] = 0;
     header->bytes += mlen + 1;
 
-    if constexpr (j6_debugcon_enable) {
-        debug_out(header->message, mlen);
-        debug_newline();
-    }
-
     util::scoped_lock lock {m_lock};
 
     uint8_t *out;
@@ -103,7 +65,7 @@ logger::output(level severity, logs area, const char *fmt, va_list args)
     memcpy(out, buffer, n);
     m_buffer.commit(n);
 
-    m_event.signal(1);
+    m_waiting.clear();
 }
 
 size_t
@@ -115,7 +77,7 @@ logger::get_entry(void *buffer, size_t size)
     size_t out_size = m_buffer.get_block(&out);
     if (out_size == 0 || out == 0) {
         lock.release();
-        m_event.wait();
+        m_waiting.wait();
         lock.reacquire();
         out_size = m_buffer.get_block(&out);
 
@@ -168,9 +130,3 @@ void fatal(logs area, const char *fmt, ...)
 }
 
 } // namespace log
-
-
-void logger_init()
-{
-    new (&g_logger) log::logger(log_buffer, sizeof(log_buffer));
-}

src/kernel/logger.h

@@ -6,6 +6,7 @@
 #include <stdint.h>
 
 #include <util/bip_buffer.h>
+#include <util/counted.h>
 #include <util/spinlock.h>
 
 #include "objects/event.h"
@@ -19,6 +20,9 @@ enum class logs : uint8_t {
 
 namespace log {
 
+/// Size of the log ring buffer
+inline constexpr unsigned log_pages = 16;
+
 enum class level : uint8_t {
     silent, fatal, error, warn, info, verbose, spam, max
 };
@@ -29,26 +33,16 @@ constexpr unsigned areas_count =
 class logger
 {
 public:
-    /// Size of the log ring buffer
-    static constexpr unsigned log_pages = 16;
-
     /// Default constructor. Creates a logger without a backing store.
     logger();
 
     /// Constructor. Logs are written to the given buffer.
     /// \arg buffer  Buffer to which logs are written
-    /// \arg size    Size of `buffer`, in bytes
-    logger(uint8_t *buffer, size_t size);
+    logger(util::buffer buffer);
 
     /// Get the default logger.
     inline logger & get() { return *s_log; }
 
-    /// Get the registered name for a given area
-    inline const char * area_name(logs area) const { return s_area_names[static_cast<unsigned>(area)]; }
-
-    /// Get the name of a level
-    inline const char * level_name(level l) const { return s_level_names[static_cast<unsigned>(l)]; }
-
     /// Write to the log
     /// \arg severity  The severity of the message
     /// \arg area      The log area to write to
@@ -100,7 +94,7 @@ private:
         return m_levels[static_cast<unsigned>(area)];
     }
 
-    obj::event m_event;
+    wait_queue m_waiting;
 
     level m_levels[areas_count];
 
@@ -108,8 +102,6 @@ private:
     util::spinlock m_lock;
 
     static logger *s_log;
-    static const char *s_area_names[areas_count+1];
-    static const char *s_level_names[static_cast<unsigned>(level::max)];
 };
 
 void spam   (logs area, const char *fmt, ...);
@@ -119,8 +111,6 @@ void warn   (logs area, const char *fmt, ...);
 void error  (logs area, const char *fmt, ...);
 void fatal  (logs area, const char *fmt, ...);
 
-extern log::logger &g_logger;
-
 } // namespace log
 
-void logger_init();
+extern log::logger &g_logger;

src/kernel/memory_bootstrap.cpp

@@ -40,6 +40,9 @@ frame_allocator &g_frame_allocator = __g_frame_allocator_storage.value;
 static util::no_construct<obj::vm_area_untracked> __g_kernel_heap_area_storage;
 obj::vm_area_untracked &g_kernel_heap_area = __g_kernel_heap_area_storage.value;
 
+static util::no_construct<obj::vm_area_ring> __g_kernel_log_area_storage;
+obj::vm_area_ring &g_kernel_log_area = __g_kernel_log_area_storage.value;
+
 static util::no_construct<obj::vm_area_untracked> __g_kernel_heapmap_area_storage;
 obj::vm_area_untracked &g_kernel_heapmap_area = __g_kernel_heapmap_area_storage.value;
 
@@ -78,7 +81,7 @@ memory_initialize_pre_ctors(bootproto::args &kargs)
 
     page_table *kpml4 = static_cast<page_table*>(kargs.pml4);
 
-
+    // Initialize the frame allocator
     frame_block *blocks = reinterpret_cast<frame_block*>(mem::bitmap_offset);
     new (&g_frame_allocator) frame_allocator {blocks, kargs.frame_blocks.count};
 
@@ -91,10 +94,11 @@ memory_initialize_pre_ctors(bootproto::args &kargs)
         reg = reg->next;
     }
 
-
+    // Initialize the kernel "process" and vm_space
     obj::process *kp = obj::process::create_kernel_process(kpml4);
     vm_space &vm = kp->space();
 
+    // Create the heap space and heap allocator
     obj::vm_area *heap = new (&g_kernel_heap_area)
         obj::vm_area_untracked(mem::heap_size, vm_flags::write);
 
@@ -106,6 +110,16 @@ memory_initialize_pre_ctors(bootproto::args &kargs)
 
     new (&g_kernel_heap) heap_allocator {mem::heap_offset, mem::heap_size, mem::heapmap_offset};
 
+    // Set up the log area and logger
+    size_t log_buffer_size = log::log_pages * arch::frame_size;
+    obj::vm_area *logs = new (&g_kernel_log_area)
+        obj::vm_area_ring(log_buffer_size, vm_flags::write);
+    vm.add(mem::logs_offset, logs);
+
+    new (&g_logger) log::logger(
+            util::buffer::from(mem::logs_offset, log_buffer_size));
+
+    // Set up the capability tables
     obj::vm_area *caps = new (&g_cap_table_area)
         obj::vm_area_untracked(mem::caps_size, vm_flags::write);
 

src/kernel/objects/vm_area.cpp

@@ -141,6 +141,11 @@ vm_area_open::get_page(uintptr_t offset, uintptr_t &phys)
     return page_tree::find_or_add(m_mapped, offset, phys);
 }
 
+void
+vm_area_open::add_existing(uintptr_t offset, uintptr_t phys)
+{
+}
+
 
 vm_area_guarded::vm_area_guarded(uintptr_t start, size_t buf_pages, size_t size, vm_flags flags) :
     m_pages {buf_pages + 1}, // Sections are N+1 pages for the leading guard page
@@ -179,4 +184,20 @@ vm_area_guarded::get_page(uintptr_t offset, uintptr_t &phys)
     return vm_area_open::get_page(offset, phys);
 }
 
+vm_area_ring::vm_area_ring(size_t size, vm_flags flags) :
+    vm_area_open {size * 2, flags},
+    m_bufsize {size}
+{
+}
+
+vm_area_ring::~vm_area_ring() {}
+
+bool
+vm_area_ring::get_page(uintptr_t offset, uintptr_t &phys)
+{
+    if (offset > m_bufsize)
+        offset -= m_bufsize;
+    return vm_area_open::get_page(offset, phys);
+}
+
 } // namespace obj

src/kernel/objects/vm_area.h

@@ -126,6 +126,10 @@ public:
 
     virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
 
+    /// Tell this VMA about an existing mapping that did not originate
+    /// from get_page.
+    void add_existing(uintptr_t offset, uintptr_t phys);
+
 private:
     page_tree *m_mapped;
 };
@@ -178,4 +182,25 @@ private:
     block_allocator m_stacks;
 };
 
+
+/// Area that maps its pages twice for use in ring buffers.
+/// Cannot be resized.
+class vm_area_ring :
+    public vm_area_open
+{
+public:
+    /// Constructor.
+    /// \arg size  Virtual size of the ring buffer. Note that
+    ///            the VMA size will be double this value.
+    /// \arg flags Flags for this memory area
+    vm_area_ring(size_t size, vm_flags flags);
+    virtual ~vm_area_ring();
+
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
+
+private:
+    size_t m_bufsize;
+    page_tree *m_mapped;
+};
+
 } // namespace obj

src/kernel/wait_queue.cpp

@@ -11,6 +11,14 @@ wait_queue::add_thread(obj::thread *t)
     m_threads.push_back(t);
 }
 
+void
+wait_queue::wait()
+{
+    obj::thread &current = obj::thread::current();
+    add_thread(&current);
+    current.block();
+}
+
 void
 wait_queue::pop_exited()
 {

src/kernel/wait_queue.h

@@ -19,6 +19,9 @@ public:
     /// queue lock.
     void add_thread(obj::thread *t);
 
+    /// Block the current thread on the queue.
+    void wait();
+
     /// Pops the next waiting thread off the queue.
     /// Locks the queue lock.
     inline obj::thread * pop_next() {