Re: [RFC v2] linux: use __fd_to_filename helper function instead of snprintf.

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

On 27/04/2021 10:09, Érico Nogueira via Libc-alpha wrote:
> Change made to fchmodat and fexecve. There are tests using xasprintf
> instead of this helper as well, but this commit doesn't touch them.

To adapt the tests it would require either to build it as internal/static
or add fd_to_filename to libsupport.  I am not this is really an improvement. 

LGTM, thanks.  I will commit this for you.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
> 
> Differences from v1:
> - actually builds
> - doesn't use an intermediary buf variable
> 
>  sysdeps/unix/sysv/linux/fchmodat.c | 13 +++----------
>  sysdeps/unix/sysv/linux/fexecve.c  | 10 ++++------
>  2 files changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/fchmodat.c b/sysdeps/unix/sysv/linux/fchmodat.c
> index f264f0c09d..5bd1eb96a5 100644
> --- a/sysdeps/unix/sysv/linux/fchmodat.c
> +++ b/sysdeps/unix/sysv/linux/fchmodat.c
> @@ -18,6 +18,7 @@
>  
>  #include <errno.h>
>  #include <fcntl.h>
> +#include <fd_to_filename.h>
>  #include <not-cancel.h>
>  #include <stdio.h>
>  #include <sys/stat.h>
> @@ -69,16 +70,8 @@ fchmodat (int fd, const char *file, mode_t mode, int flag)
>  
>        /* For most file systems, fchmod does not operate on O_PATH
>  	 descriptors, so go through /proc.  */
> -      char buf[32];
> -      if (__snprintf (buf, sizeof (buf), "/proc/self/fd/%d", pathfd) < 0)
> -	{
> -	  /* This also may report strange error codes to the caller
> -	     (although snprintf really should not fail).  */
> -	  __close_nocancel (pathfd);
> -	  return -1;
> -	}
> -
> -      int ret = __chmod (buf, mode);
> +      struct fd_to_filename filename;
> +      int ret = __chmod (__fd_to_filename (pathfd, &filename), mode);
>        if (ret != 0)
>  	{
>  	  if (errno == ENOENT)
> diff --git a/sysdeps/unix/sysv/linux/fexecve.c b/sysdeps/unix/sysv/linux/fexecve.c
> index f37c245396..df25c2acb8 100644
> --- a/sysdeps/unix/sysv/linux/fexecve.c
> +++ b/sysdeps/unix/sysv/linux/fexecve.c
> @@ -22,6 +22,7 @@
>  #include <fcntl.h>
>  #include <sys/stat.h>
>  
> +#include <fd_to_filename.h>
>  #include <sysdep.h>
>  #include <sys/syscall.h>
>  #include <kernel-features.h>
> @@ -49,12 +50,9 @@ fexecve (int fd, char *const argv[], char *const envp[])
>  
>  #ifndef __ASSUME_EXECVEAT
>    /* We use the /proc filesystem to get the information.  If it is not
> -     mounted we fail.  */
> -  char buf[sizeof "/proc/self/fd/" + sizeof (int) * 3];
> -  __snprintf (buf, sizeof (buf), "/proc/self/fd/%d", fd);
> -
> -  /* We do not need the return value.  */
> -  __execve (buf, argv, envp);
> +     mounted we fail.  We do not need the return value.  */
> +  struct fd_to_filename filename;
> +  __execve (__fd_to_filename (fd, &filename), argv, envp);
>  
>    int save = errno;
>  
>