Re: [Qemu-devel] [PATCH] Fix utimensat (aka unbreak cp -a)

[Martin Mohring]

i found another related case it seems:

when i call in a chroot under arm with qemu user mode:

$ touch /var/log/wtmp

the resulting file has a date/time of 1.1.1970, although the clock is
correct in the system.

calling

$ touch /var/log/wtmp /var/run/utmp /var/log/btmp
/bin/touch: setting times of `/var/run/utmp': Invalid argument
/bin/touch: setting times of `/var/log/btmp': Invalid argument

results in the invalid argutment error. I ll currently check which
syscalls are involved here.
the time of 1.1.1970 looks to me like a wrongly passed argument (of ==0).

Riku Voipio wrote:
> On Tue, Apr 21, 2009 at 10:24:03AM +0200, Arnaud Patard wrote:
>   
>> Don't use the glibc function for utimensat because glibc returns -EINVAL
>> if the path is null which is a different behaviour with the syscall.
>> path can be null because internally the glibc is using utimensat with
>> path null (for instance, see __futimes in
>> sysdeps/unix/sysv/linux/futimes.c in glibc tree).
>>     
>
> Soo.. glibc uses utimensat to implement futimens, but doesn't allow
> applications to use utimensat in the same way. What a mess.
>
> But if we are to go towards using libc calls, your patch is a step
> backwards. In case pathname is null, we can use futimens.
>
>
> commit 0f34ff059fb9ad6e8c8fa5161d9d17265286bb62
> Author: Riku Voipio <address@hidden>
> Date:   Tue Apr 21 15:01:51 2009 +0300
>
>     linux-user: fix utimensat when used as futimens
>     
>     The glibc function for utimensat glibc returns -EINVAL when the path is 
> null
>     which is a different behaviour with the syscall.
>     
>     path can be null because internally the glibc is using utimensat with
>     path null when implmenting futimens. If path is null, call futimes
>     instead.
>
> diff --git a/configure b/configure
> index 08df436..fc980a4 100755
> --- a/configure
> +++ b/configure
> @@ -1208,6 +1208,25 @@ EOF
>    fi
>  fi
>  
> +# check if utimensat and futimens are supported
> +utimens=no
> +cat > $TMPC << EOF
> +#define _ATFILE_SOURCE
> +#define _GNU_SOURCE
> +#include <stddef.h>
> +#include <fcntl.h>
> +
> +int main(void)
> +{
> +    utimensat(AT_FDCWD, "foo", NULL, 0);
> +    futimens(0, NULL);
> +    return 0;
> +}
> +EOF
> +if $cc $ARCH_CFLAGS -o $TMPE $TMPC 2> /dev/null ; then
> +  utimens=yes
> +fi
> +
>  # Check if tools are available to build documentation.
>  if [ -x "`which texi2html 2>/dev/null`" ] && \
>     [ -x "`which pod2man 2>/dev/null`" ]; then
> @@ -1604,6 +1623,9 @@ fi
>  if test "$atfile" = "yes" ; then
>    echo "#define CONFIG_ATFILE 1" >> $config_h
>  fi
> +if test "$utimens" = "yes" ; then
> +  echo "#define CONFIG_UTIMENSAT 1" >> $config_h
> +fi
>  if test "$inotify" = "yes" ; then
>    echo "#define CONFIG_INOTIFY 1" >> $config_h
>  fi
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 408ccc6..4dad5c1 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -406,13 +406,6 @@ static int sys_unlinkat(int dirfd, const char *pathname, 
> int flags)
>    return (unlinkat(dirfd, pathname, flags));
>  }
>  #endif
> -#ifdef TARGET_NR_utimensat
> -static int sys_utimensat(int dirfd, const char *pathname,
> -    const struct timespec times[2], int flags)
> -{
> -  return (utimensat(dirfd, pathname, times, flags));
> -}
> -#endif
>  #else /* !CONFIG_ATFILE */
>  
>  /*
> @@ -476,12 +469,24 @@ _syscall3(int,sys_symlinkat,const char *,oldpath,
>  #if defined(TARGET_NR_unlinkat) && defined(__NR_unlinkat)
>  _syscall3(int,sys_unlinkat,int,dirfd,const char *,pathname,int,flags)
>  #endif
> +
> +#endif /* CONFIG_ATFILE */
> +
> +#ifdef CONFIG_UTIMENSAT
> +static int sys_utimensat(int dirfd, const char *pathname,
> +    const struct timespec times[2], int flags)
> +{
> +    if (pathname == NULL)
> +        return futimens(dirfd, times);
> +    else
> +        return utimensat(dirfd, pathname, times, flags);
> +}
> +#else
>  #if defined(TARGET_NR_utimensat) && defined(__NR_utimensat)
>  _syscall4(int,sys_utimensat,int,dirfd,const char *,pathname,
>            const struct timespec *,tsp,int,flags)
>  #endif
> -
> -#endif /* CONFIG_ATFILE */
> +#endif /* CONFIG_UTIMENSAT  */
>  
>  #ifdef CONFIG_INOTIFY
>  #include <sys/inotify.h>
>
>
>