kernel+libc: Add a memstat() syscall

We can finally show memory usage in userspace.

This could have been done using sysfs, but I'm lazy and don't want to implement that. Maybe in the next release?

kernel/CMakeLists.txt

@@ -47,6 +47,7 @@ set(SOURCES
     src/sys/poll.cpp
     src/sys/alarm.cpp
     src/sys/pledge.cpp
+    src/sys/memstat.cpp
     src/fs/VFS.cpp
     src/fs/Pipe.cpp
     src/fs/Mount.cpp

kernel/src/sys/memstat.cpp

@@ -0,0 +1,21 @@
+#include "Pledge.h"
+#include "memory/MemoryManager.h"
+#include "sys/Syscall.h"
+#include "thread/Scheduler.h"
+#include <bits/memstat.h>
+
+Result<u64> sys_memstat(Registers*, SyscallArgs args)
+{
+    auto* current = Scheduler::current();
+    TRY(check_pledge(current, Promise::p_stdio));
+
+    struct membuf buf;
+    buf.mem_total = MemoryManager::total();
+    buf.mem_used = MemoryManager::used();
+    buf.mem_free = MemoryManager::free();
+    buf.mem_reserved = MemoryManager::reserved();
+
+    if (!MemoryManager::copy_to_user_typed((struct membuf*)args[0], &buf)) return err(EFAULT);
+
+    return 0;
+}

libc/CMakeLists.txt

@@ -33,6 +33,7 @@ set(SOURCES
     src/sys/utsname.cpp
     src/sys/mount.cpp
     src/sys/pstat.cpp
+    src/sys/memstat.cpp
     src/sys/resource.cpp
     src/sys/socket.cpp
     src/sys/poll.cpp

libc/include/bits/memstat.h

@@ -0,0 +1,14 @@
+/* bits/memstat.h: The membuf structure for memstat(). */
+
+#ifndef _BITS_MEMSTAT_H
+#define _BITS_MEMSTAT_H
+
+struct membuf
+{
+    unsigned long mem_total;
+    unsigned long mem_used;
+    unsigned long mem_free;
+    unsigned long mem_reserved;
+};
+
+#endif

libc/include/sys/memstat.h

@@ -0,0 +1,20 @@
+/* sys/memstat.h: Memory usage querying. */
+
+#ifndef _SYS_MEMSTAT_H
+#define _SYS_MEMSTAT_H
+
+#include <bits/memstat.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    /* Query system memory usage. */
+    int memstat(struct membuf* mem);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

libc/src/sys/memstat.cpp

@@ -0,0 +1,13 @@
+#include <bits/errno-return.h>
+#include <sys/memstat.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+extern "C"
+{
+    int memstat(struct membuf* buf)
+    {
+        long rc = syscall(SYS_memstat, buf);
+        __errno_return(rc, int);
+    }
+}

libluna/include/luna/Syscall.h

@@ -8,7 +8,7 @@
                     _e(umount) _e(pstat) _e(getrusage) _e(symlinkat) _e(readlinkat) _e(umask) _e(linkat) _e(faccessat) \
                         _e(pivot_root) _e(sigreturn) _e(sigaction) _e(kill) _e(sigprocmask) _e(setpgid) _e(isatty)     \
                             _e(getpgid) _e(socket) _e(bind) _e(connect) _e(listen) _e(accept) _e(poll) _e(msync)       \
-                                _e(truncate) _e(ftruncate) _e(utimensat) _e(alarm) _e(pledge)
+                                _e(truncate) _e(ftruncate) _e(utimensat) _e(alarm) _e(pledge) _e(memstat)
 
 enum Syscalls
 {