[PATCH v2 1/3] support: Add support_fcntl_support_ofd_locks ()

[Adhemerval Zanella Netto]

On 28/05/23 14:20, Sergey Bugaev via Libc-alpha wrote:
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>

LGTM, thanks.

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

> ---
> 
> support_xxx_support_yyy () seems to be the naming pattern for this
> kind of functions?

That's the pattern I use to follow.

> 
>  support/Makefile                          |  1 +
>  support/support.h                         |  3 ++
>  support/support_fcntl_support_ofd_locks.c | 44 +++++++++++++++++++++++
>  3 files changed, 48 insertions(+)
>  create mode 100644 support/support_fcntl_support_ofd_locks.c
> 
> diff --git a/support/Makefile b/support/Makefile
> index 92f1a246..e9a00b2d 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -58,6 +58,7 @@ libsupport-routines = \
>    support_descriptors \
>    support_enter_mount_namespace \
>    support_enter_network_namespace \
> +  support_fcntl_support_ofd_locks \
>    support_format_address_family \
>    support_format_addrinfo \
>    support_format_dns_packet \
> diff --git a/support/support.h b/support/support.h
> index b7f76bf0..e20d2ce7 100644
> --- a/support/support.h
> +++ b/support/support.h
> @@ -178,6 +178,9 @@ static __inline bool support_itimer_support_time64 (void)
>  #endif
>  }
>  
> +/* Return true if the kernel/file supports open file description locks.  */
> +extern bool support_fcntl_support_ofd_locks (int fd);
> +
>  /* Return true if stat supports nanoseconds resolution.  PATH is used
>     for tests and its ctime may change.  */
>  extern bool support_stat_nanoseconds (const char *path);
> diff --git a/support/support_fcntl_support_ofd_locks.c b/support/support_fcntl_support_ofd_locks.c
> new file mode 100644
> index 00000000..fb197a70
> --- /dev/null
> +++ b/support/support_fcntl_support_ofd_locks.c
> @@ -0,0 +1,44 @@
> +/* Return whether the kernel/file supports OFD locks.
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   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
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <support/support.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <string.h>
> +
> +bool
> +support_fcntl_support_ofd_locks (int fd)
> +{
> +#ifdef F_OFD_GETLK
> +  int res;
> +  struct flock flock;
> +  memset (&flock, 0, sizeof (flock));
> +
> +  flock.l_type = F_WRLCK;
> +  flock.l_whence = SEEK_SET;
> +  flock.l_start = 0;
> +  flock.l_len = INT32_MAX;
> +  flock.l_pid = 0;
> +
> +  res = fcntl (fd, F_OFD_GETLK, &flock);
> +  return res != -1 || errno != EINVAL;

I think returning an unexpected error here as supported should be ok here.

> +#else
> +  (void) fd;
> +  return false;
> +#endif
> +}