ladybird/Kernel/Syscalls/fork.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/FileDescription.h>
#include <Kernel/Process.h>
#include <Kernel/SharedBuffer.h>
#include <Kernel/VM/Region.h>

//#define FORK_DEBUG

namespace Kernel {

pid_t Process::sys$fork(RegisterState& regs)
{
    REQUIRE_PROMISE(proc);
    RefPtr<Thread> child_first_thread;
    auto child = adopt(*new Process(child_first_thread, m_name, m_uid, m_gid, m_pid, m_is_kernel_process, m_cwd, m_executable, m_tty, this));
    if (!child_first_thread)
        return -ENOMEM;
    child->m_root_directory = m_root_directory;
    child->m_root_directory_relative_to_global_root = m_root_directory_relative_to_global_root;
    child->m_promises = m_promises;
    child->m_execpromises = m_execpromises;
    child->m_veil_state = m_veil_state;
    child->m_unveiled_paths = m_unveiled_paths;
    child->m_fds = m_fds;
    child->m_sid = m_sid;
    child->m_pg = m_pg;
    child->m_umask = m_umask;

#ifdef FORK_DEBUG
    dbg() << "fork: child=" << child;
#endif

    child->m_extra_gids = m_extra_gids;

    auto& child_tss = child_first_thread->m_tss;
    child_tss.eax = 0; // fork() returns 0 in the child :^)
    child_tss.ebx = regs.ebx;
    child_tss.ecx = regs.ecx;
    child_tss.edx = regs.edx;
    child_tss.ebp = regs.ebp;
    child_tss.esp = regs.userspace_esp;
    child_tss.esi = regs.esi;
    child_tss.edi = regs.edi;
    child_tss.eflags = regs.eflags;
    child_tss.eip = regs.eip;
    child_tss.cs = regs.cs;
    child_tss.ds = regs.ds;
    child_tss.es = regs.es;
    child_tss.fs = regs.fs;
    child_tss.gs = regs.gs;
    child_tss.ss = regs.userspace_ss;

#ifdef FORK_DEBUG
    dbgln("fork: child will begin executing at {:04x}:{:08x} with stack {:04x}:{:08x}, kstack {:04x}:{:08x}", child_tss.cs, child_tss.eip, child_tss.ss, child_tss.esp, child_tss.ss0, child_tss.esp0);
#endif

    SharedBuffer::share_all_shared_buffers(*this, *child);

    {
        ScopedSpinLock lock(m_lock);
        for (auto& region : m_regions) {
#ifdef FORK_DEBUG
            dbg() << "fork: cloning Region{" << &region << "} '" << region.name() << "' @ " << region.vaddr();
#endif
            auto& child_region = child->add_region(region.clone());
            child_region.map(child->page_directory());

            if (&region == m_master_tls_region.unsafe_ptr())
                child->m_master_tls_region = child_region;
        }

        ScopedSpinLock processes_lock(g_processes_lock);
        g_processes->prepend(child);
        child->ref(); // This reference will be dropped by Process::reap
    }

    ScopedSpinLock lock(g_scheduler_lock);
    child_first_thread->set_affinity(Thread::current()->affinity());
    child_first_thread->set_state(Thread::State::Runnable);
    return child->pid().value();
}

}