Re: [musl] [PATCH] dirent: implement getdents64

[Rich Felker <dalias@libc.org>]

On Tue, May 24, 2022 at 04:07:04PM +0800, Jiaqing Zhao wrote:
> In musl, getdents64 is an alias of getdents, but the type annotation
> of these two functions are different according to man page[1], causing
> compile errors. This patch implements the standard getdents64.
>     ssize_t getdents64(int fd, void *dirp, size_t count);
> 
> [1] https://man7.org/linux/man-pages/man2/getdents.2.html
> 
> Signed-off-by: Jiaqing Zhao <jiaqing.zhao@linux.intel.com>
> ---
>  include/dirent.h     | 3 ++-
>  src/linux/getdents.c | 6 +++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/dirent.h b/include/dirent.h
> index 650ecf64..4c5367c2 100644
> --- a/include/dirent.h
> +++ b/include/dirent.h
> @@ -11,6 +11,7 @@ extern "C" {
>  #define __NEED_off_t
>  #if defined(_BSD_SOURCE) || defined(_GNU_SOURCE)
>  #define __NEED_size_t
> +#define __NEED_ssize_t
>  #endif
>  
>  #include <bits/alltypes.h>
> @@ -50,6 +51,7 @@ long           telldir(DIR *);
>  #define IFTODT(x) ((x)>>12 & 017)
>  #define DTTOIF(x) ((x)<<12)
>  int getdents(int, struct dirent *, size_t);
> +ssize_t getdents64(int, void *, size_t);
>  #endif
>  
>  #ifdef _GNU_SOURCE
> @@ -65,7 +67,6 @@ int versionsort(const struct dirent **, const struct dirent **);
>  #define versionsort64 versionsort
>  #define off64_t off_t
>  #define ino64_t ino_t
> -#define getdents64 getdents
>  #endif
>  
>  #ifdef __cplusplus
> diff --git a/src/linux/getdents.c b/src/linux/getdents.c
> index 796c1e5c..923a8076 100644
> --- a/src/linux/getdents.c
> +++ b/src/linux/getdents.c
> @@ -9,4 +9,8 @@ int getdents(int fd, struct dirent *buf, size_t len)
>  	return syscall(SYS_getdents, fd, buf, len);
>  }
>  
> -weak_alias(getdents, getdents64);
> +ssize_t getdents64(int fd, void *buf, size_t len)
> +{
> +	if (len>INT_MAX) len = INT_MAX;
> +	return syscall(SYS_getdents64, fd, buf, len);
> +}
> -- 
> 2.34.1

The inclusion of LFS64 API stuff in musl was a historical mistake that
resulted from attempting glibc ABI-compat, not a set of interfaces we
want. What happened was that the weak aliases for glibc ABI compat
were included, then broken configure scripts that checked only for
symbol linkage but not for a working declaration "detected" these
functions as usable, producing miscompiled code from lack of
declartion. Since it was intended that musl-built programs never
reference these ABI-compat-only symbols, it was "fixed" by adding the
macros to redirect them to the correct functions, but this caused lots
of problems and we're still trying to extricate the mess. If at some
point the glibc ABI-compat stuff can be moved entirely to the external
gcompat project, the macros will be removed entirely.

As such, I think this patch is not appropriate for inclusion.

Rich