fs/driver/fs_blockproxy.c

/****************************************************************************
 * fs/driver/fs_blockproxy.c
 *
 * Copyright (c) 2023 Huawei Device Co., Ltd. All rights reserved.
 * Based on NuttX originally from nuttx source (nuttx/fs/ and nuttx/drivers/)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <semaphore.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include "fs/driver.h"
#include "blockproxy.h"

#ifdef LOSCFG_FS_VFS_BLOCK_DEVICE

/****************************************************************************
 * Private Data
 ****************************************************************************/

static uint32_t g_devno;
static sem_t g_devno_sem;

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: unique_chardev
 *
 * Description:
 *   Create a unique temporary device name in the /dev/ directory of the
 *   pseudo-file system.  We cannot use mktemp for this because it will
 *   attempt to open() the file.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   The allocated path to the device.  This must be released by the caller
 *   to prevent memory links.  NULL will be returned only the case where
 *   we fail to allocate memory.
 *
 ****************************************************************************/

static char *unique_chardev(void)
{
  struct stat statbuf;
  char devbuf[16];
  uint32_t devno;
  int ret;

  /* Loop until we get a unique device name */

  for (; ;)
    {
      /* Get the semaphore protecting the path number */

      while (sem_wait(&g_devno_sem) != 0)
        {
          /* The only case that an error should occur here is if the wait
           * was awakened by a signal.
           */

          ret = get_errno();
          LOS_ASSERT(ret == EINTR);
        }

      /* Get the next device number and release the semaphore */

      devno = ++g_devno;
      (void)sem_post(&g_devno_sem);

      /* Construct the full device number */

      devno &= 0xffffff;
      ret = snprintf_s(devbuf, 16, 14, "/dev/tmp%06lx", (unsigned long)devno);
      /* length of the format string is 14 */
      if (ret < 0)
        {
          set_errno(ENAMETOOLONG);
          return strdup(devbuf);
        }

      /* Make sure that file name is not in use */

      ret = stat(devbuf, &statbuf);
      if (ret < 0)
        {
          DEBUGASSERT(errno == ENOENT);
          return strdup(devbuf);
        }

      /* It is in use, try again */
    }
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: block_proxy
 *
 * Description:
 *   Create a temporary char driver using drivers/bch to mediate character
 *   oriented accessed to the block driver.
 *
 * Input Parameters:
 *   blkdev - The path to the block driver
 *   oflags - Character driver open flags
 *
 * Returned Value:
 *   If positive, non-zero file descriptor is returned on success.  This
 *   is the file descriptor of the nameless character driver that mediates
 *   accesses to the block driver.
 *
 *   Errors that may be returned:
 *
 *     ENOMEM - Failed to create a temporay path name.
 *
 *   Plus:
 *
 *     - Errors reported from bchdev_register()
 *     - Errors reported from open() or unlink()
 *
 ****************************************************************************/

int block_proxy(const char *blkdev, int oflags)
{
  struct file *filep = NULL;
  struct Vnode *vnode = NULL;
  char *chardev;
  bool readonly;
  int ret;
  int fd;

  DEBUGASSERT(blkdev);
  (void)sem_init(&g_devno_sem, 0, 1);

  /* Create a unique temporary file name for the character device */

  chardev = unique_chardev();
  if (chardev == NULL)
    {
      PRINTK("ERROR: Failed to create temporary device name\n");
      (void)sem_destroy(&g_devno_sem);
      return -ENOMEM;
    }

  /* Should this character driver be read-only? */

  readonly = (((unsigned int)oflags & O_ACCMODE) == O_RDONLY);

  /* Wrap the block driver with an instance of the BCH driver */

  ret = bchdev_register(blkdev, chardev, readonly);
  if (ret < 0)
    {
      PRINTK("ERROR: bchdev_register(%s, %s) failed: %d\n", blkdev, chardev, ret);
      goto errout_with_chardev;
    }

  /* Open the newly created character driver */

  oflags =(unsigned int)oflags & (~(O_CREAT | O_EXCL | O_APPEND | O_TRUNC));
  fd = open(chardev, oflags);
  if (fd < 0)
    {
      ret = -errno;
      PRINTK("ERROR: Failed to open %s: %d\n", chardev, ret);
      goto errout_with_bchdev;
    }

  ret = fs_getfilep(fd, &filep);
  if (ret < 0)
    {
      files_release(fd);
      ret = -get_errno();
      goto errout_with_bchdev;
    }

  vnode = filep->f_vnode;
  VnodeHold();
  vnode->type = VNODE_TYPE_BCHR;
  VnodeDrop();

  /* Free the allocate character driver name and return the open file
   * descriptor.
   */

  (void)free(chardev);
  (void)sem_destroy(&g_devno_sem);
  return fd;

errout_with_bchdev:
  (void)unregister_driver(chardev);
errout_with_chardev:
  (void)free(chardev);
  (void)sem_destroy(&g_devno_sem);
  return ret;
}

#endif