pupy/client/sources-linux/memfd.h

#ifndef _PUPY_MEMFD_H
#define _PUPY_MEMFD_H

#define _GNU_SOURCE
#include <sys/syscall.h>
#include <string.h>
#include <stdbool.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>

#ifndef MFD_CLOEXEC
  #define MFD_CLOEXEC         0x0001U
  #define MFD_ALLOW_SEALING   0x0002U
#endif

#ifndef __NR_memfd_create
 #ifdef __x86_64__
  #define __NR_memfd_create 319
 #elif __i386__
  #define __NR_memfd_create 356
 #elif __arm__
  #define __NR_memfd_create 385
 #endif
#endif

#ifndef F_ADD_SEALS
  #define F_ADD_SEALS    (1024 + 9)
  #define F_SEAL_SEAL    0x0001
  #define F_SEAL_SHRINK  0x0002
  #define F_SEAL_GROW    0x0004
  #define F_SEAL_WRITE   0x0008
#endif

#define PROCFS_PATH "/proc/"
#define MEMFD_FILE_PATH PROCFS_PATH "%d/fd/"

static bool memfd_checked = false;
static bool memfd_works = true;

inline static bool pupy_memfd_supported()
{
  int fd;

  if (memfd_checked)
    return memfd_works;

  fd = syscall(__NR_memfd_create, "check", MFD_CLOEXEC | MFD_ALLOW_SEALING);
  close(fd);

  return fd != -1;
}

inline static int pupy_memfd_create(char *path, unsigned int path_size)
{
#ifdef Linux

#ifdef DEBUG
    #define _path path
#else
    char _path[PATH_MAX] = "libc.so.6";
#endif

    /* Do not make syscall billion times */
    if (memfd_checked && !memfd_works) {
      errno = ENOSYS;
      return -1;
    }

    int fd = syscall(__NR_memfd_create, _path, MFD_CLOEXEC | MFD_ALLOW_SEALING);

    if (fd == -1) {
      if (errno == ENOSYS)
        memfd_works = false;

      return -1;
    }

    snprintf(path, path_size, MEMFD_FILE_PATH "%d", getpid(), fd);
    return fd;
#else
  return -1;
#endif
}

inline static bool is_memfd_path(const char *path)
{
    return !strncmp(path, PROCFS_PATH, strlen(PROCFS_PATH)) && \
        strstr(path, "/fd/");
}
#endif