Re: [PATCH 2/5] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS

[Greg Kurz]

On Tue, 19 Apr 2022 13:41:03 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> mknod() on macOS does not support creating sockets, so divert to
> call sequence socket(), bind() and chmod() respectively if S_IFSOCK
> was passed with mode argument.
> 

Hmm... thinking again about this one : QEMU on linux calls the libc
version of mknodat() which doesn't seem to support S_IFSOCK according
to the mknod(3P) manual page. So I'm not sure there's something to
be actually fixed here... what's the observed behavior on linux ?

> Link: https://lore.kernel.org/qemu-devel/17933734.zYzKuhC07K@silver/
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> ---
>  hw/9pfs/9p-util-darwin.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
> index 53e0625501..252a6fc5dd 100644
> --- a/hw/9pfs/9p-util-darwin.c
> +++ b/hw/9pfs/9p-util-darwin.c
> @@ -74,6 +74,24 @@ int fsetxattrat_nofollow(int dirfd, const char *filename, 
> const char *name,
>   */
>  #if defined CONFIG_PTHREAD_FCHDIR_NP
>  
> +static int create_socket_file_at_cwd(const char *filename, mode_t mode) {
> +    int fd, err;
> +    struct sockaddr_un addr = {
> +        .sun_family = AF_UNIX
> +    };
> +
> +    fd = socket(PF_UNIX, SOCK_DGRAM, 0);
> +    if (fd < 0) {
> +        return fd;
> +    }
> +    snprintf(addr.sun_path, sizeof(addr.sun_path), "./%s", filename);
> +    err = bind(fd, (struct sockaddr *) &addr, sizeof(addr));
> +    if (err < 0) {
> +        return err;
> +    }
> +    return chmod(addr.sun_path, mode);
> +}
> +
>  int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
>  {
>      int preserved_errno, err;
> @@ -88,7 +106,11 @@ int qemu_mknodat(int dirfd, const char *filename, mode_t 
> mode, dev_t dev)
>      if (pthread_fchdir_np(dirfd) < 0) {
>          return -1;
>      }
> -    err = mknod(filename, mode, dev);
> +    if (S_ISSOCK(mode)) {
> +        err = create_socket_file_at_cwd(filename, mode);
> +    } else {
> +        err = mknod(filename, mode, dev);
> +    }
>      preserved_errno = errno;
>      /* Stop using the thread-local cwd */
>      pthread_fchdir_np(-1);