Re: [PATCH v4 1/6] 9pfs: fix qemu_mknodat(S_IFREG) on macOS

[Greg Kurz]

On Wed, 27 Apr 2022 20:54:04 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> mknod() on macOS does not support creating regular files, so
> divert to openat_file() if S_IFREG is passed with mode argument.
> 
> Furthermore, 'man 2 mknodat' on Linux says: "Zero file type is
> equivalent to type S_IFREG".
> 

Thinking again I have mixed feelings about this... qemu_mknodat()
should certainly match POSIX semantics, even non-portable, as
described in [1] but I'm not sure it should mimic linux-specific
behaviors.

[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/mknod.html

> Link: https://lore.kernel.org/qemu-devel/17933734.zYzKuhC07K@silver/
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> Reviewed-by: Will Cohen <wwcohen@gmail.com>
> Reviewed-by: Greg Kurz <groug@kaod.org>
> ---
>  hw/9pfs/9p-util-darwin.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
> index bec0253474..e24d09763a 100644
> --- a/hw/9pfs/9p-util-darwin.c
> +++ b/hw/9pfs/9p-util-darwin.c
> @@ -77,6 +77,15 @@ int fsetxattrat_nofollow(int dirfd, const char *filename, 
> const char *name,
>  int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
>  {
>      int preserved_errno, err;
> +
> +    if (S_ISREG(mode) || !(mode & S_IFMT)) {

... so maybe I'd just check S_ISREG() here. Not a request, just food
for thought : sticking to POSIX semantics might help to make the code
more portable across all the new host supports that are showing up
these days.

> +        int fd = openat_file(dirfd, filename, O_CREAT, mode);
> +        if (fd == -1) {
> +            return fd;
> +        }
> +        close(fd);
> +        return 0;
> +    }
>      if (!pthread_fchdir_np) {
>          error_report_once("pthread_fchdir_np() not available on this version 
> of macOS");
>          return -ENOTSUP;