Re: [PATCH v6 02/21] util/char_dev: Add open_cdev()

["Cédric Le Goater" <clg@redhat.com>]

On 11/14/23 11:09, Zhenzhong Duan wrote:
> From: Yi Liu <yi.l.liu@intel.com>
> 
> /dev/vfio/devices/vfioX may not exist. In that case it is still possible
> to open /dev/char/$major:$minor instead. Add helper function to abstract
> the cdev open.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
>   MAINTAINERS                 |  3 ++
>   include/qemu/chardev_open.h | 16 ++++++++
>   util/chardev_open.c         | 81 +++++++++++++++++++++++++++++++++++++
>   util/meson.build            |  1 +
>   4 files changed, 101 insertions(+)
>   create mode 100644 include/qemu/chardev_open.h
>   create mode 100644 util/chardev_open.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a4891f7bda..869ec3d5af 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2172,6 +2172,9 @@ M: Eric Auger <eric.auger@redhat.com>
>   S: Supported
>   F: backends/iommufd.c
>   F: include/sysemu/iommufd.h
> +F: include/qemu/chardev_open.h
> +F: util/chardev_open.c
> +
>   
>   vhost
>   M: Michael S. Tsirkin <mst@redhat.com>
> diff --git a/include/qemu/chardev_open.h b/include/qemu/chardev_open.h
> new file mode 100644
> index 0000000000..64e8fcfdcb
> --- /dev/null
> +++ b/include/qemu/chardev_open.h
> @@ -0,0 +1,16 @@
> +/*
> + * QEMU Chardev Helper
> + *
> + * Copyright (C) 2023 Intel Corporation.
> + *
> + * Authors: Yi Liu <yi.l.liu@intel.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + */
> +
> +#ifndef QEMU_CHARDEV_OPEN_H
> +#define QEMU_CHARDEV_OPEN_H
> +
> +int open_cdev(const char *devpath, dev_t cdev);
> +#endif
> diff --git a/util/chardev_open.c b/util/chardev_open.c
> new file mode 100644
> index 0000000000..f776429788
> --- /dev/null
> +++ b/util/chardev_open.c
> @@ -0,0 +1,81 @@
> +/*
> + * Copyright (c) 2019, Mellanox Technologies. All rights reserved.
> + * Copyright (C) 2023 Intel Corporation.
> + *
> + * This software is available to you under a choice of one of two
> + * licenses.  You may choose to be licensed under the terms of the GNU
> + * General Public License (GPL) Version 2, available from the file
> + * COPYING in the main directory of this source tree, or the
> + * OpenIB.org BSD license below:
> + *
> + *      Redistribution and use in source and binary forms, with or
> + *      without modification, are permitted provided that the following
> + *      conditions are met:
> + *
> + *      - Redistributions of source code must retain the above
> + *        copyright notice, this list of conditions and the following
> + *        disclaimer.
> + *
> + *      - Redistributions in binary form must reproduce the above
> + *        copyright notice, this list of conditions and the following
> + *        disclaimer in the documentation and/or other materials
> + *        provided with the distribution.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
> + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
> + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
> + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
> + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + *
> + * Authors: Yi Liu <yi.l.liu@intel.com>
> + *
> + * Copied from
> + * https://github.com/linux-rdma/rdma-core/blob/master/util/open_cdev.c
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/chardev_open.h"
> +
> +static int open_cdev_internal(const char *path, dev_t cdev)
> +{
> +    struct stat st;
> +    int fd;
> +
> +    fd = qemu_open_old(path, O_RDWR);
> +    if (fd == -1) {
> +        return -1;
> +    }
> +    if (fstat(fd, &st) || !S_ISCHR(st.st_mode) ||
> +        (cdev != 0 && st.st_rdev != cdev)) {
> +        close(fd);
> +        return -1;
> +    }
> +    return fd;
> +}
> +
> +static int open_cdev_robust(dev_t cdev)
> +{
> +    g_autofree char *devpath = NULL;
> +
> +    /*
> +     * This assumes that udev is being used and is creating the /dev/char/
> +     * symlinks.
> +     */
> +    devpath = g_strdup_printf("/dev/char/%u:%u", major(cdev), minor(cdev));
> +    return open_cdev_internal(devpath, cdev);
> +}
> +
> +int open_cdev(const char *devpath, dev_t cdev)
> +{
> +    int fd;
> +
> +    fd = open_cdev_internal(devpath, cdev);
> +    if (fd == -1 && cdev != 0) {
> +        return open_cdev_robust(cdev);
> +    }
> +    return fd;
> +}
> diff --git a/util/meson.build b/util/meson.build
> index c2322ef6e7..174c133368 100644
> --- a/util/meson.build
> +++ b/util/meson.build
> @@ -108,6 +108,7 @@ if have_block
>       util_ss.add(files('filemonitor-stub.c'))
>     endif
>     util_ss.add(when: 'CONFIG_LINUX', if_true: files('vfio-helpers.c'))
> +  util_ss.add(when: 'CONFIG_LINUX', if_true: files('chardev_open.c'))
>   endif
>   
>   if cpu == 'aarch64'