Re: [PATCH v3 5/6] util/async-teardown: Use qemu_close_range() to close fds

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Sat, 17 Jun 2023 13:36:20 +0800
Bin Meng <bmeng@tinylab.org> wrote:

> From: Zhangjin Wu <falcon@tinylab.org>
> 
> Based on the old close_all_open_fd() of util/async-teardown.c, a new
> generic qemu_close_range() has been added in osdep.c.
> 
> Now, let's switch over to use the generic qemu_close_range().
> 
> Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
> Signed-off-by: Bin Meng <bmeng@tinylab.org>
> 
> ---
> 
> Changes in v3:
> - limit the last_fd of qemu_close_range() to sysconf(_SC_OPEN_MAX)
> 
> Changes in v2:
> - new patch: "util/async-teardown: Use qemu_close_range() to close fds"
> 
>  util/async-teardown.c | 42 ++----------------------------------------
>  1 file changed, 2 insertions(+), 40 deletions(-)
> 
> diff --git a/util/async-teardown.c b/util/async-teardown.c
> index 7e0177a8da..e102912f3f 100644
> --- a/util/async-teardown.c
> +++ b/util/async-teardown.c
> @@ -29,44 +29,6 @@
>  
>  static pid_t the_ppid;
>  
> -/*
> - * Close all open file descriptors.
> - */
> -static void close_all_open_fd(void)
> -{
> -    struct dirent *de;
> -    int fd, dfd;
> -    DIR *dir;
> -
> -#ifdef CONFIG_CLOSE_RANGE
> -    int r = close_range(0, ~0U, 0);
> -    if (!r) {
> -        /* Success, no need to try other ways. */
> -        return;
> -    }
> -#endif
> -
> -    dir = opendir("/proc/self/fd");
> -    if (!dir) {
> -        /* If /proc is not mounted, close fds one by one. */
> -        int open_max = sysconf(_SC_OPEN_MAX), i;
> -        for (i = 0; i < open_max; i++) {
> -                close(i);
> -        }
> -        return;
> -    }
> -    /* Avoid closing the directory. */
> -    dfd = dirfd(dir);
> -
> -    for (de = readdir(dir); de; de = readdir(dir)) {
> -        fd = atoi(de->d_name);
> -        if (fd != dfd) {
> -            close(fd);
> -        }
> -    }
> -    closedir(dir);
> -}
> -
>  static void hup_handler(int signal)
>  {
>      /* Check every second if this process has been reparented. */
> @@ -84,6 +46,7 @@ static int async_teardown_fn(void *arg)
>      struct sigaction sa = { .sa_handler = hup_handler };
>      sigset_t hup_signal;
>      char name[16];
> +    int open_max = sysconf(_SC_OPEN_MAX);
>  
>      /* Set a meaningful name for this process. */
>      snprintf(name, 16, "cleanup/%d", the_ppid);
> @@ -92,9 +55,8 @@ static int async_teardown_fn(void *arg)
>      /*
>       * Close all file descriptors that might have been inherited from the
>       * main qemu process when doing clone, needed to make libvirt happy.
> -     * Not using close_range for increased compatibility with older kernels.
>       */
> -    close_all_open_fd();
> +    qemu_close_range(0, open_max - 1);

I think it would look easier to read if you just put the sysconf() call
here and avoid an extra variable

>  
>      /* Set up a handler for SIGHUP and unblock SIGHUP. */
>      sigaction(SIGHUP, &sa, NULL);