Expose the kernel log buffer through /proc/dmesg.

Also add a /bin/dmesg program for convenience.

Kernel/Console.cpp

@@ -52,6 +52,7 @@ void Console::put_char(char ch)
     //if (ch != 27)
     IO::out8(0xe9, ch);
 #endif
+    m_logbuffer.enqueue(ch);
     if (m_implementation)
         m_implementation->on_sysconsole_receive(ch);
 }

Kernel/Console.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <AK/CircularQueue.h>
 #include <AK/Compiler.h>
 #include <AK/Vector.h>
 #include <Kernel/CharacterDevice.h>
@@ -29,7 +30,10 @@ public:
 
     void put_char(char);
 
+    const CircularQueue<char, 16384>& logbuffer() const { return m_logbuffer; }
+
 private:
     ConsoleImplementation* m_implementation { nullptr };
+    CircularQueue<char, 16384> m_logbuffer;
 };
 

Kernel/ProcFileSystem.cpp

@@ -6,6 +6,7 @@
 #include "StdLib.h"
 #include "i386.h"
 #include "KSyms.h"
+#include "Console.h"
 #include <AK/StringBuilder.h>
 
 static ProcFS* s_the;
@@ -198,6 +199,15 @@ ByteBuffer procfs$mm(SynthFSInode&)
     return builder.to_byte_buffer();
 }
 
+ByteBuffer procfs$dmesg(SynthFSInode&)
+{
+    InterruptDisabler disabler;
+    StringBuilder builder;
+    for (char ch : Console::the().logbuffer())
+        builder.append(ch);
+    return builder.to_byte_buffer();
+}
+
 ByteBuffer procfs$mounts(SynthFSInode&)
 {
     InterruptDisabler disabler;
@@ -386,6 +396,7 @@ bool ProcFS::initialize()
     add_file(create_generated_file("summary", procfs$summary));
     add_file(create_generated_file("cpuinfo", procfs$cpuinfo));
     add_file(create_generated_file("inodes", procfs$inodes));
+    add_file(create_generated_file("dmesg", procfs$dmesg));
     m_sys_dir = add_file(create_directory("sys"));
     return true;
 }

Kernel/sync.sh

@@ -49,6 +49,7 @@ cp -v ../Userland/guitest mnt/bin/guitest
 cp -v ../Userland/guitest2 mnt/bin/guitest2
 cp -v ../Userland/sysctl mnt/bin/sysctl
 cp -v ../Terminal/Terminal mnt/bin/Terminal
+cp -v ../Userland/dmesg mnt/bin/dmesg
 sh sync-local.sh
 cp -v kernel.map mnt/
 ln -s dir_a mnt/dir_cur