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

["Érico Nogueira via Libc-alpha" <libc-alpha@sourceware.org>]

On Mon May 3, 2021 at 4:26 PM -03, Adhemerval Zanella wrote:
>
>
> 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.

That might explain some of the build failures I got when I tried
changing the tests.

>
> LGTM, thanks. I will commit this for you.

Thanks!

I found a few more places where __fd_to_filename could be used, they are
currently using _fitoa_word together with stpcpy. Would you be
interested in making __fd_to_filename use _fitoa_word or _itoa_word? Or
should it be left as is?

>
> 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;
> >  
> >