LinuxSystem.cs

using System;
using System.Runtime.InteropServices;

namespace fault
{
    // Warning: I did the minimum required to get a sample working
    // Warning: Be careful using this.

    public class LinuxSystem
    {
        private const string LIBC_6 = "libc";

        [DllImport(LIBC_6, EntryPoint = "syscall", SetLastError = true)]
        public static extern long syscall1(long number, int a0);

        [DllImport(LIBC_6, EntryPoint = "ioctl", SetLastError = true)]
        public static extern int ioctl(int fd, int cmd, ref uffdio_api arg);

        [DllImport(LIBC_6, EntryPoint = "ioctl", SetLastError = true)]
        public static extern int ioctl(int fd, int cmd, ref uffdio_register arg);

        [DllImport(LIBC_6, EntryPoint = "mmap64", SetLastError = true)]
        public static extern nint mmap64(nint start, nuint length,
          MmapProts prot, MmapFlags flags, int fd, long offset);


        [Flags]
        public enum MmapFlags : int
        {
            MAP_SHARED = 0x01,     // Share changes.
            MAP_PRIVATE = 0x02,     // Changes are private.
            MAP_TYPE = 0x0f,     // Mask for type of mapping.
            MAP_FIXED = 0x10,     // Interpret addr exactly.
            MAP_FILE = 0,
            MAP_ANONYMOUS = 0x20,     // Don't use a file.
            MAP_ANON = MAP_ANONYMOUS,

            // These are Linux-specific.
            MAP_GROWSDOWN = 0x00100,  // Stack-like segment.
            MAP_DENYWRITE = 0x00800,  // ETXTBSY
            MAP_EXECUTABLE = 0x01000,  // Mark it as an executable.
            MAP_LOCKED = 0x02000,  // Lock the mapping.
            MAP_NORESERVE = 0x04000,  // Don't check for reservations.
            MAP_POPULATE = 0x08000,  // Populate (prefault) pagetables.
            MAP_NONBLOCK = 0x10000,  // Do not block on IO.
        }

        [Flags]
        public enum MmapProts : int
        {
            PROT_READ = 0x1,  // Page can be read.
            PROT_WRITE = 0x2,  // Page can be written.
            PROT_EXEC = 0x4,  // Page can be executed.
            PROT_NONE = 0x0,  // Page can not be accessed.
            PROT_GROWSDOWN = 0x01000000, // Extend change to start of
                                         //   growsdown vma (mprotect only).
            PROT_GROWSUP = 0x02000000, // Extend change to start of
                                       //   growsup vma (mprotect only).
        }

        public const int SYS_userfaultfd = 323;
        public const ulong UFFD_API = 170;
        public const int UFFDIO_API = unchecked((int)3222841919);
        public const int UFFDIO_REGISTER = unchecked((int)3223366144);
        public const int UFFDIO_REGISTER_MODE_MISSING = 1;
        public const int UFFD_API_RANGE_IOCTLS = 28;
        public const int UFFD_EVENT_PAGEFAULT = 18;

        [Flags]

        public enum OpenFlags : int
        {
            O_RDONLY = 0x00000000,
            O_WRONLY = 0x00000001,
            O_RDWR = 0x00000002,
            O_NONBLOCK = 0x00000800,
        }

        public struct uffdio_api
        {
            public ulong api;        /* Requested API version (input) */
            public ulong features;   /* Requested features (input/output) */
            public ulong ioctls;     /* Available ioctl() operations (output) */
        };


        public struct uffdio_range
        {
            public ulong start;    /* Start of range */
            public ulong len;      /* Length of range (bytes) */
        };

        public struct uffdio_register
        {
            public uffdio_range range;
            public ulong mode;     /* Desired mode of operation (input) */
            public ulong ioctls;   /* Available ioctl() operations (output) */
        };

        public struct uffd_msg_pagefault_feat
        {
            public uint ptid;
        }

        public struct uffd_msg_fork
        {
            public uint ufd;
        }
        public struct uffd_msg_remap
        {
            public ulong from;
            public ulong to;
            public ulong len;
        }
        public struct uffd_msg_remove
        {
            public ulong start;
            public ulong end;
        }


        public struct uffd_msg_pagefault
        {
            public ulong flags;
            public ulong address;
            public uffd_msg_pagefault_feat feat;
        }

        [StructLayout(LayoutKind.Explicit)]
        public unsafe struct uffd_msg
        {
            [FieldOffset(0)]
            public byte @event;

            [FieldOffset(1)]
            public fixed byte reserved[7];

            [FieldOffset(8)]
            public uffd_msg_pagefault pagefault;

            [FieldOffset(8)]
            public uffd_msg_fork fork;

            [FieldOffset(8)]
            public uffd_msg_remap remap;

            [FieldOffset(8)]
            public uffd_msg_remove remove;
        }


        public static int userfaultfd(OpenFlags flags)
        {
            return (int)syscall1(SYS_userfaultfd, (int)flags);
        }

    }
}