More work towards getting bash to build.

Implemented some syscalls: dup(), dup2(), getdtablesize().
FileHandle is now a retainable, since that's needed for dup()'ed fd's.
I didn't really test any of this beyond a basic smoke check.

Kernel/Process.cpp

@@ -1158,7 +1158,6 @@ int Process::sys$open(const char* path, int options)
         if (!m_file_descriptors[fd])
             break;
     }
-    handle->setFD(fd);
     m_file_descriptors[fd] = move(handle);
     return fd;
 }
@@ -1435,3 +1434,35 @@ int Process::sys$tcsetpgrp(int fd, pid_t pgid)
     tty.set_pgid(pgid);
     return 0;
 }
+
+int Process::sys$getdtablesize()
+{
+    return m_max_open_file_descriptors;
+}
+
+int Process::sys$dup(int old_fd)
+{
+    auto* handle = fileHandleIfExists(old_fd);
+    if (!handle)
+        return -EBADF;
+    if (number_of_open_file_descriptors() == m_max_open_file_descriptors)
+        return -EMFILE;
+    int new_fd = 0;
+    for (; new_fd < m_max_open_file_descriptors; ++new_fd) {
+        if (!m_file_descriptors[new_fd])
+            break;
+    }
+    m_file_descriptors[new_fd] = handle;
+    return new_fd;
+}
+
+int Process::sys$dup2(int old_fd, int new_fd)
+{
+    auto* handle = fileHandleIfExists(old_fd);
+    if (!handle)
+        return -EBADF;
+    if (number_of_open_file_descriptors() == m_max_open_file_descriptors)
+        return -EMFILE;
+    m_file_descriptors[new_fd] = handle;
+    return new_fd;
+}

Kernel/Process.h

@@ -126,6 +126,9 @@ public:
     int sys$execve(const char* filename, const char** argv, const char** envp);
     Unix::sighandler_t sys$signal(int signum, Unix::sighandler_t);
     int sys$isatty(int fd);
+    int sys$getdtablesize();
+    int sys$dup(int oldfd);
+    int sys$dup2(int oldfd, int newfd);
 
     static void initialize();
 
@@ -193,7 +196,7 @@ private:
     State m_state { Invalid };
     DWORD m_wakeupTime { 0 };
     TSS32 m_tss;
-    Vector<OwnPtr<FileHandle>> m_file_descriptors;
+    Vector<RetainPtr<FileHandle>> m_file_descriptors;
     RingLevel m_ring { Ring0 };
     int m_error { 0 };
     void* m_kernelStack { nullptr };

Kernel/Syscall.cpp

@@ -140,6 +140,12 @@ static DWORD handle(RegisterDump& regs, DWORD function, DWORD arg1, DWORD arg2,
         return (dword)current->sys$signal((int)arg1, (Unix::sighandler_t)arg2);
     case Syscall::PosixIsatty:
         return current->sys$isatty((int)arg1);
+    case Syscall::Getdtablesize:
+        return current->sys$getdtablesize();
+    case Syscall::Dup:
+        return current->sys$dup((int)arg1);
+    case Syscall::Dup2:
+        return current->sys$dup2((int)arg1, (int)arg2);
     default:
         kprintf("<%u> int0x80: Unknown function %x requested {%x, %x, %x}\n", current->pid(), function, arg1, arg2, arg3);
         break;

Kernel/Syscall.h

@@ -53,6 +53,9 @@ enum Function {
     PosixGetegid = 0x2021,
     PosixSignal = 0x2022,
     PosixIsatty = 0x2023,
+    Getdtablesize = 0x2024,
+    Dup = 0x2025,
+    Dup2 = 0x2026,
 };
 
 void initialize();