Kernel+LibC: Support passing O_CLOEXEC to pipe()

In the userspace, this mimics the Linux pipe2() syscall;
in the kernel, the Process::sys$pipe() now always accepts
a flags argument, the no-argument pipe() syscall is now a
userspace wrapper over pipe2().

Kernel/Process.cpp

@@ -1194,20 +1194,25 @@ int Process::alloc_fd(int first_candidate_fd)
     return fd;
 }
 
-int Process::sys$pipe(int pipefd[2])
+int Process::sys$pipe(int pipefd[2], int flags)
 {
     if (!validate_write_typed(pipefd))
         return -EFAULT;
     if (number_of_open_file_descriptors() + 2 > max_open_file_descriptors())
         return -EMFILE;
+    // Reject flags other than O_CLOEXEC.
+    if ((flags & O_CLOEXEC) != flags)
+        return -EINVAL;
+
+    u32 fd_flags = (flags & O_CLOEXEC) ? FD_CLOEXEC : 0;
     auto fifo = FIFO::create(m_uid);
 
     int reader_fd = alloc_fd();
-    m_fds[reader_fd].set(fifo->open_direction(FIFO::Direction::Reader));
+    m_fds[reader_fd].set(fifo->open_direction(FIFO::Direction::Reader), fd_flags);
     pipefd[0] = reader_fd;
 
     int writer_fd = alloc_fd();
-    m_fds[writer_fd].set(fifo->open_direction(FIFO::Direction::Writer));
+    m_fds[writer_fd].set(fifo->open_direction(FIFO::Direction::Writer), fd_flags);
     pipefd[1] = writer_fd;
 
     return 0;

Kernel/Process.h

@@ -168,7 +168,7 @@ public:
     int sys$sigpending(sigset_t*);
     int sys$getgroups(ssize_t, gid_t*);
     int sys$setgroups(ssize_t, const gid_t*);
-    int sys$pipe(int* pipefd);
+    int sys$pipe(int pipefd[2], int flags);
     int sys$killpg(int pgrp, int sig);
     int sys$setgid(gid_t);
     int sys$setuid(uid_t);

Kernel/Syscall.cpp

@@ -189,7 +189,7 @@ static u32 handle(RegisterDump& regs, u32 function, u32 arg1, u32 arg2, u32 arg3
     case Syscall::SC_sigprocmask:
         return current->process().sys$sigprocmask((int)arg1, (const sigset_t*)arg2, (sigset_t*)arg3);
     case Syscall::SC_pipe:
-        return current->process().sys$pipe((int*)arg1);
+        return current->process().sys$pipe((int*)arg1, (int) arg2);
     case Syscall::SC_killpg:
         return current->process().sys$killpg((int)arg1, (int)arg2);
     case Syscall::SC_setuid:

Libraries/LibC/unistd.cpp

@@ -366,7 +366,12 @@ int getgroups(int size, gid_t list[])
 
 int pipe(int pipefd[2])
 {
-    int rc = syscall(SC_pipe, pipefd);
+    return pipe2(pipefd, 0);
+}
+
+int pipe2(int pipefd[2], int flags)
+{
+    int rc = syscall(SC_pipe, pipefd, flags);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 

Libraries/LibC/unistd.h

@@ -86,6 +86,7 @@ int getdtablesize();
 int dup(int old_fd);
 int dup2(int old_fd, int new_fd);
 int pipe(int pipefd[2]);
+int pipe2(int pipefd[2], int flags);
 unsigned int alarm(unsigned int seconds);
 int access(const char* pathname, int mode);
 int isatty(int fd);