Re: [PATCH] Implement the mlock2 function

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 24/11/2017 14:59, Florian Weimer wrote:
> diff --git a/sysdeps/unix/sysv/linux/mlock2.c b/sysdeps/unix/sysv/linux/mlock2.c
> new file mode 100644
> index 0000000000..1646cfb9e1
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/mlock2.c
> @@ -0,0 +1,40 @@
> +/* Wrapper for the mlock2 system call with fallback to mlock.
> +   Copyright (C) 2017 Free Software Foundation, Inc.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <sys/mman.h>
> +#include <errno.h>
> +#include <sysdep.h>
> +
> +int
> +mlock2 (const void *addr, size_t length, unsigned int flags)
> +{
> +#ifdef __ASSUME_MLOCK2
> +  return INLINE_SYSCALL (mlock2, 3, addr, length, flags);
> +#else
> +  if (flags == 0)
> +    return INLINE_SYSCALL (mlock, 2, addr, length);
> +# ifdef __NR_mlock2
> +  int ret = INLINE_SYSCALL (mlock2, 3, addr, length, flags);
> +  if (ret == 0 || errno != ENOSYS)
> +    return ret;
> +# endif /* __NR_mlock2 */
> +  /* Treat the missing system call as an invalid (non-zero) flag
> +     argument.  */
> +  __set_errno (EINVAL);
> +  return -1;
> +#endif /* __ASSUME_MLOCK2 */
> +}

We have the INLINE_SYSCALL_CALL to simplify and avoid issue with mismatch
input number and arguments (which is not this case).

I am not sure if it is better to advertise EINVAL for ENOSYS mainly
because it won't be transparent on a syscall trace.  But I do not have
a strong opinion here.