util/chardev_open.c

   1 /*
   2  * Copyright (c) 2019, Mellanox Technologies. All rights reserved.
   3  * Copyright (C) 2023 Intel Corporation.
   4  *
   5  * This software is available to you under a choice of one of two
   6  * licenses.  You may choose to be licensed under the terms of the GNU
   7  * General Public License (GPL) Version 2, available from the file
   8  * COPYING in the main directory of this source tree, or the
   9  * OpenIB.org BSD license below:
  10  *
  11  *      Redistribution and use in source and binary forms, with or
  12  *      without modification, are permitted provided that the following
  13  *      conditions are met:
  14  *
  15  *      - Redistributions of source code must retain the above
  16  *        copyright notice, this list of conditions and the following
  17  *        disclaimer.
  18  *
  19  *      - Redistributions in binary form must reproduce the above
  20  *        copyright notice, this list of conditions and the following
  21  *        disclaimer in the documentation and/or other materials
  22  *        provided with the distribution.
  23  *
  24  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  25  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  26  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  27  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  28  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  29  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  30  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  31  * SOFTWARE.
  32  *
  33  * Authors: Yi Liu <yi.l.liu@intel.com>
  34  *
  35  * Copied from
  36  * https://github.com/linux-rdma/rdma-core/blob/master/util/open_cdev.c
  37  *
  38  */
  39
  40 #include "qemu/osdep.h"
  41 #include "qemu/chardev_open.h"
  42
  43 static int open_cdev_internal(const char *path, dev_t cdev)
  44 {
  45     struct stat st;
  46     int fd;
  47
  48     fd = qemu_open_old(path, O_RDWR);
  49     if (fd == -1) {
  50         return -1;
  51     }
  52     if (fstat(fd, &st) || !S_ISCHR(st.st_mode) ||
  53         (cdev != 0 && st.st_rdev != cdev)) {
  54         close(fd);
  55         return -1;
  56     }
  57     return fd;
  58 }
  59
  60 static int open_cdev_robust(dev_t cdev)
  61 {
  62     g_autofree char *devpath = NULL;
  63
  64     /*
  65      * This assumes that udev is being used and is creating the /dev/char/
  66      * symlinks.
  67      */
  68     devpath = g_strdup_printf("/dev/char/%u:%u", major(cdev), minor(cdev));
  69     return open_cdev_internal(devpath, cdev);
  70 }
  71
  72 int open_cdev(const char *devpath, dev_t cdev)
  73 {
  74     int fd;
  75
  76     fd = open_cdev_internal(devpath, cdev);
  77     if (fd == -1 && cdev != 0) {
  78         return open_cdev_robust(cdev);
  79     }
  80     return fd;
  81 }