Re: [PATCH v5 09/11] 9p: darwin: Implement compatibility for mknodat

["Philippe Mathieu-Daudé via" <qemu-devel@nongnu.org>]

On 7/2/22 23:40, Will Cohen wrote:
> From: Keno Fischer <keno@juliacomputing.com>
> 
> Darwin does not support mknodat. However, to avoid race conditions
> with later setting the permissions, we must avoid using mknod on
> the full path instead. We could try to fchdir, but that would cause
> problems if multiple threads try to call mknodat at the same time.
> However, luckily there is a solution: Darwin includes a function
> that sets the cwd for the current thread only.
> This should suffice to use mknod safely.
> 
> This function (pthread_fchdir_np) is protected by a check in
> meson in a patch later in tihs series.
> 
> Signed-off-by: Keno Fischer <keno@juliacomputing.com>
> Signed-off-by: Michael Roitzsch <reactorcontrol@icloud.com>
> [Will Cohen: - Adjust coding style
>               - Replace clang references with gcc
>               - Note radar filed with Apple for missing syscall
>               - Replace direct syscall with pthread_fchdir_np and
>                 adjust patch notes accordingly
>               - Move qemu_mknodat from 9p-util to osdep and os-posix]
> Signed-off-by: Will Cohen <wwcohen@gmail.com>
> ---
>   hw/9pfs/9p-local.c   |  4 ++--
>   include/qemu/osdep.h | 10 ++++++++++
>   os-posix.c           | 34 ++++++++++++++++++++++++++++++++++
>   3 files changed, 46 insertions(+), 2 deletions(-)

> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index d1660d67fa..f3a8367ece 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -810,3 +810,13 @@ static inline int platform_does_not_support_system(const char *command)
>   #endif
>   
>   #endif
> +
> +/*
> + * As long as mknodat is not available on macOS, this workaround
> + * using pthread_fchdir_np is needed. qemu_mknodat is defined in
> + * os-posix.c
> + */
> +#ifdef CONFIG_DARWIN
> +int pthread_fchdir_np(int fd);
> +#endif
> +int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev);

Misplaced. You want the declaration before the __cplusplus guard.