LibC+Kernel: Start implementing sysconf

For now, only the non-standard _SC_NPROCESSORS_CONF and
_SC_NPROCESSORS_ONLN are implemented.

Use them to make ninja pick a better default -j value.
While here, make the ninja package script not fail if
no other port has been built yet.

Kernel/API/Syscall.h

@@ -191,7 +191,8 @@ namespace Kernel {
     __ENUMERATE_SYSCALL(ptrace)             \
     __ENUMERATE_SYSCALL(minherit)           \
     __ENUMERATE_SYSCALL(sendfd)             \
-    __ENUMERATE_SYSCALL(recvfd)
+    __ENUMERATE_SYSCALL(recvfd)             \
+    __ENUMERATE_SYSCALL(sysconf)
 
 namespace Syscall {
 

Kernel/Arch/i386/CPU.h

@@ -744,6 +744,8 @@ public:
 
     static Processor& by_id(u32 cpu);
 
+    static size_t processor_count() { return processors().size(); }
+
     template<typename Callback>
     static inline IterationDecision for_each(Callback callback)
     {

Kernel/Process.cpp

@@ -5308,4 +5308,15 @@ int Process::sys$recvfd(int sockfd)
     m_fds[new_fd].set(*received_descriptor_or_error.value(), 0);
     return new_fd;
 }
+
+long Process::sys$sysconf(int name)
+{
+    switch (name) {
+    case _SC_NPROCESSORS_CONF:
+    case _SC_NPROCESSORS_ONLN:
+        return Processor::processor_count();
+    default:
+        return -EINVAL;
+    }
+}
 }

Kernel/Process.h

@@ -327,6 +327,7 @@ public:
     int sys$ptrace(const Syscall::SC_ptrace_params*);
     int sys$sendfd(int sockfd, int fd);
     int sys$recvfd(int sockfd);
+    long sys$sysconf(int name);
 
     template<bool sockname, typename Params>
     int get_sock_or_peer_name(const Params&);

Kernel/UnixTypes.h

@@ -55,6 +55,11 @@
 #define MS_RDONLY (1 << 4)
 #define MS_REMOUNT (1 << 5)
 
+enum {
+    _SC_NPROCESSORS_CONF,
+    _SC_NPROCESSORS_ONLN,
+};
+
 #define PERF_EVENT_MALLOC 1
 #define PERF_EVENT_FREE 2