buse.c

/*
 * buse - block-device userspace extensions
 * Copyright (C) 2013 Adam Cozzette
 *
 * This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _POSIX_C_SOURCE (200809L)

#include <assert.h>
#include <errno.h>
#include <err.h>
#include <fcntl.h>
#include <linux/nbd.h>
#include <netinet/in.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>

#include "buse.h"

#ifndef BUSE_DEBUG
  #define BUSE_DEBUG (0)
#endif

/*
 * These helper functions were taken from cliserv.h in the nbd distribution.
 */
#ifdef WORDS_BIGENDIAN
u_int64_t ntohll(u_int64_t a) {
  return a;
}
#else
u_int64_t ntohll(u_int64_t a) {
  u_int32_t lo = a & 0xffffffff;
  u_int32_t hi = a >> 32U;
  lo = ntohl(lo);
  hi = ntohl(hi);
  return ((u_int64_t) lo) << 32U | hi;
}
#endif
#define htonll ntohll

static int read_all(int fd, char* buf, size_t count)
{
  int bytes_read;

  while (count > 0) {
    bytes_read = read(fd, buf, count);
    assert(bytes_read > 0);
    buf += bytes_read;
    count -= bytes_read;
  }
  assert(count == 0);

  return 0;
}

static int write_all(int fd, char* buf, size_t count)
{
  int bytes_written;

  while (count > 0) {
    bytes_written = write(fd, buf, count);
    assert(bytes_written > 0);
    buf += bytes_written;
    count -= bytes_written;
  }
  assert(count == 0);

  return 0;
}

/* Signal handler to gracefully disconnect from nbd kernel driver. */
static int nbd_dev_to_disconnect = -1;
static void disconnect_nbd(int signal) {
  (void)signal;
  if (nbd_dev_to_disconnect != -1) {
    if(ioctl(nbd_dev_to_disconnect, NBD_DISCONNECT) == -1) {
      warn("failed to request disconect on nbd device");
    } else {
      nbd_dev_to_disconnect = -1;
      fprintf(stderr, "sucessfuly requested disconnect on nbd device\n");
    }
  }
}

/* Sets signal action like regular sigaction but is suspicious. */
static int set_sigaction(int sig, const struct sigaction * act) {
  struct sigaction oact;
  int r = sigaction(sig, act, &oact);
  if (r == 0 && oact.sa_handler != SIG_DFL) {
    warnx("overriden non-default signal handler (%d: %s)", sig, strsignal(sig));
  }
  return r;
}

/* Serve userland side of nbd socket. If everything worked ok, return 0. */
static int serve_nbd(int sk, const struct buse_operations * aop, void * userdata) {
  u_int64_t from;
  u_int32_t len;
  ssize_t bytes_read;
  struct nbd_request request;
  struct nbd_reply reply;
  void *chunk;

  reply.magic = htonl(NBD_REPLY_MAGIC);
  reply.error = htonl(0);

  while ((bytes_read = read(sk, &request, sizeof(request))) > 0) {
    assert(bytes_read == sizeof(request));
    memcpy(reply.handle, request.handle, sizeof(reply.handle));
    reply.error = htonl(0);

    len = ntohl(request.len);
    from = ntohll(request.from);
    assert(request.magic == htonl(NBD_REQUEST_MAGIC));

    switch(ntohl(request.type)) {
      /* I may at some point need to deal with the the fact that the
       * official nbd server has a maximum buffer size, and divides up
       * oversized requests into multiple pieces. This applies to reads
       * and writes.
       */
    case NBD_CMD_READ:
      if (BUSE_DEBUG) fprintf(stderr, "Request for read of size %d\n", len);
      /* Fill with zero in case actual read is not implemented */
      chunk = malloc(len);
      if (aop->read) {
        reply.error = aop->read(chunk, len, from, userdata);
      } else {
        /* If user not specified read operation, return EPERM error */
        reply.error = htonl(EPERM);
      }
      write_all(sk, (char*)&reply, sizeof(struct nbd_reply));
      write_all(sk, (char*)chunk, len);

      free(chunk);
      break;
    case NBD_CMD_WRITE:
      if (BUSE_DEBUG) fprintf(stderr, "Request for write of size %d\n", len);
      chunk = malloc(len);
      read_all(sk, chunk, len);
      if (aop->write) {
        reply.error = aop->write(chunk, len, from, userdata);
      } else {
        /* If user not specified write operation, return EPERM error */
        reply.error = htonl(EPERM);
      }
      free(chunk);
      write_all(sk, (char*)&reply, sizeof(struct nbd_reply));
      break;
    case NBD_CMD_DISC:
      if (BUSE_DEBUG) fprintf(stderr, "Got NBD_CMD_DISC\n");
      /* Handle a disconnect request. */
      if (aop->disc) {
        aop->disc(userdata);
      }
      return EXIT_SUCCESS;
#ifdef NBD_FLAG_SEND_FLUSH
    case NBD_CMD_FLUSH:
      if (BUSE_DEBUG) fprintf(stderr, "Got NBD_CMD_FLUSH\n");
      if (aop->flush) {
        reply.error = aop->flush(userdata);
      }
      write_all(sk, (char*)&reply, sizeof(struct nbd_reply));
      break;
#endif
#ifdef NBD_FLAG_SEND_TRIM
    case NBD_CMD_TRIM:
      if (BUSE_DEBUG) fprintf(stderr, "Got NBD_CMD_TRIM\n");
      if (aop->trim) {
        reply.error = aop->trim(from, len, userdata);
      }
      write_all(sk, (char*)&reply, sizeof(struct nbd_reply));
      break;
#endif
    default:
      assert(0);
    }
  }
  if (bytes_read == -1) {
    warn("error reading userside of nbd socket");
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}

int buse_main(const char* dev_file, const struct buse_operations *aop, void *userdata)
{
  int sp[2];
  int nbd, sk, err, flags;

  err = socketpair(AF_UNIX, SOCK_STREAM, 0, sp);
  assert(!err);

  nbd = open(dev_file, O_RDWR);
  if (nbd == -1) {
    fprintf(stderr, 
        "Failed to open `%s': %s\n"
        "Is kernel module `nbd' loaded and you have permissions "
        "to access the device?\n", dev_file, strerror(errno));
    return 1;
  }

  if (aop->blksize) {
    err = ioctl(nbd, NBD_SET_BLKSIZE, aop->blksize);
    assert(err != -1);
  }
  if (aop->size) {
    err = ioctl(nbd, NBD_SET_SIZE, aop->size);
    assert(err != -1);
  }
  if (aop->size_blocks) {
    err = ioctl(nbd, NBD_SET_SIZE_BLOCKS, aop->size_blocks);
    assert(err != -1);
  }

  err = ioctl(nbd, NBD_CLEAR_SOCK);
  assert(err != -1);

  pid_t pid = fork();
  if (pid == 0) {
    /* Block all signals to not get interrupted in ioctl(NBD_DO_IT), as
     * it seems there is no good way to handle such interruption.*/
    sigset_t sigset;
    if (
      sigfillset(&sigset) != 0 ||
      sigprocmask(SIG_SETMASK, &sigset, NULL) != 0
    ) {
      warn("failed to block signals in child");
      exit(EXIT_FAILURE);
    }

    /* The child needs to continue setting things up. */
    close(sp[0]);
    sk = sp[1];

    if(ioctl(nbd, NBD_SET_SOCK, sk) == -1){
      fprintf(stderr, "ioctl(nbd, NBD_SET_SOCK, sk) failed.[%s]\n", strerror(errno));
      exit(EXIT_FAILURE);
    }
    else{
#if defined NBD_SET_FLAGS
      flags = 0;
#if defined NBD_FLAG_SEND_TRIM
      flags |= NBD_FLAG_SEND_TRIM;
#endif
#if defined NBD_FLAG_SEND_FLUSH
      flags |= NBD_FLAG_SEND_FLUSH;
#endif
      if (flags != 0 && ioctl(nbd, NBD_SET_FLAGS, flags) == -1){
        fprintf(stderr, "ioctl(nbd, NBD_SET_FLAGS, %d) failed.[%s]\n", flags, strerror(errno));
        exit(EXIT_FAILURE);
      }
#endif
      err = ioctl(nbd, NBD_DO_IT);
      if (BUSE_DEBUG) fprintf(stderr, "nbd device terminated with code %d\n", err);
      if (err == -1) {
        warn("NBD_DO_IT terminated with error");
        exit(EXIT_FAILURE);
      }
    }

    if (
      ioctl(nbd, NBD_CLEAR_QUE) == -1 ||
      ioctl(nbd, NBD_CLEAR_SOCK) == -1
    ) {
      warn("failed to perform nbd cleanup actions");
      exit(EXIT_FAILURE);
    }

    exit(0);
  }

  /* Parent handles termination signals by terminating nbd device. */
  assert(nbd_dev_to_disconnect == -1);
  nbd_dev_to_disconnect = nbd;
  struct sigaction act;
  act.sa_handler = disconnect_nbd;
  act.sa_flags = SA_RESTART;
  if (
    sigemptyset(&act.sa_mask) != 0 ||
    sigaddset(&act.sa_mask, SIGINT) != 0 ||
    sigaddset(&act.sa_mask, SIGTERM) != 0
  ) {
    warn("failed to prepare signal mask in parent");
    return EXIT_FAILURE;
  }
  if (
    set_sigaction(SIGINT, &act) != 0 ||
    set_sigaction(SIGTERM, &act) != 0
  ) {
    warn("failed to register signal handlers in parent");
    return EXIT_FAILURE;
  }

  close(sp[1]);

  /* serve NBD socket */
  int status;
  status = serve_nbd(sp[0], aop, userdata);
  if (close(sp[0]) != 0) warn("problem closing server side nbd socket");
  if (status != 0) return status;

  /* wait for subprocess */
  if (waitpid(pid, &status, 0) == -1) {
    warn("waitpid failed");
    return EXIT_FAILURE;
  }
  if (WEXITSTATUS(status) != 0) {
    return WEXITSTATUS(status);
  }

  return EXIT_SUCCESS;
}