Re: [musl] [PATCH v1] add renameat2 linux syscall wrapper

[Rich Felker <dalias@libc.org>]

On Sun, Apr 21, 2024 at 08:36:40AM -0700, Tony Ambardar wrote:
> This syscall is available since Linux 3.15 and also implemented in glibc
> from version 2.28. It is commonly used in filesystem or security contexts.
> 
> Defines RENAME_NOREPLACE, RENAME_EXCHANGE, RENAME_WHITEOUT are guarded by
> _GNU_SOURCE as with glibc.
> 
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---
>  include/stdio.h       | 7 +++++++
>  src/linux/renameat2.c | 8 ++++++++
>  2 files changed, 15 insertions(+)
>  create mode 100644 src/linux/renameat2.c
> 
> diff --git a/include/stdio.h b/include/stdio.h
> index cb858618..8312c3bf 100644
> --- a/include/stdio.h
> +++ b/include/stdio.h
> @@ -158,6 +158,13 @@ char *ctermid(char *);
>  #define L_ctermid 20
>  #endif
>  
> +#if defined(_GNU_SOURCE)
> +#define RENAME_NOREPLACE (1 << 0)
> +#define RENAME_EXCHANGE (1 << 1)
> +#define RENAME_WHITEOUT (1 << 2)
> +
> +int renameat2(int, const char *, int, const char *, unsigned int);
> +#endif

s/unsigned int/unsigned/ and maybe just write out the constants? I
think that's the style musl uses most places.

>  #if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
>   || defined(_BSD_SOURCE)
> diff --git a/src/linux/renameat2.c b/src/linux/renameat2.c
> new file mode 100644
> index 00000000..3062aa15
> --- /dev/null
> +++ b/src/linux/renameat2.c
> @@ -0,0 +1,8 @@
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include "syscall.h"
> +
> +int renameat2(int oldfd, const char *old, int newfd, const char *new, unsigned int flags)
> +{
> +	return syscall(SYS_renameat2, oldfd, old, newfd, new, flags);
> +}
> -- 
> 2.34.1

This probably at least needs to support flags==0 on kernels without
SYS_renameat2 by calling renameat in that case. Then I'm not sure if
ENOSYS should be kept if the new syscall is missing, or just EINVAL or
whatever is used to report unsupported flags.

Rich