Re: [PATCH v2] io: Refactor close_range and closefrom

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

If no one oposes it I will commit this shortly.

On 08/11/2021 14:28, Adhemerval Zanella wrote:
> Now that Hurd implementis both close_range and closefrom (f2c996597d),
> we can make close_range() a base ABI, and make the default closefrom()
> implementation on top of close_range().
> 
> The generic closefrom() implementation based on __getdtablesize() is
> moved to generic close_range().  On Linux it will be overriden by
> the auto-generation syscall while on Hurd it will be a system specific
> implementation.
> 
> The closefrom() now calls close_range() and __closefrom_fallback().
> Since on Hurd close_range() does not fail, __closefrom_fallback() is an
> empty static inline function set by__ASSUME_CLOSE_RANGE.
> 
> The __ASSUME_CLOSE_RANGE also allows optimize Linux
> __closefrom_fallback() implementation when --enable-kernel=5.9 or
> higher is used.
> 
> Finally the Linux specific tst-close_range.c is moved to io and
> enabled as default.  The Linuxism and CLOSE_RANGE_UNSHARE are
> guarded so it can be built for Hurd (I have not actually test it).
> 
> Checked on x86_64-linux-gnu, i686-linux-gnu, and with a i686-gnu
> build.
> ---
> Changes from v1:
>   - Changed close_range() comment to specify close() errors are
>     ignored.
>   - Fixed close_range() default implementation.
>   - __closefrom_fallback() for __ASSUME_CLOSE_RANGE.
> ---
>  include/unistd.h                              | 10 ++++++
>  io/Makefile                                   |  3 +-
>  .../linux/closefrom.c => io/close_range.c     | 34 ++++++++++++-------
>  io/closefrom.c                                | 16 +++++----
>  .../unix/sysv/linux => io}/tst-close_range.c  |  8 +++++
>  posix/unistd.h                                | 10 ++++++
>  sysdeps/mach/hurd/Makefile                    |  2 +-
>  sysdeps/mach/hurd/bits/unistd_ext.h           |  6 ----
>  sysdeps/mach/hurd/closefrom.c                 | 29 ----------------
>  sysdeps/mach/hurd/kernel-features.h           |  2 ++
>  sysdeps/unix/sysv/linux/Makefile              |  1 -
>  sysdeps/unix/sysv/linux/bits/unistd_ext.h     |  9 -----
>  sysdeps/unix/sysv/linux/closefrom_fallback.c  |  4 +++
>  sysdeps/unix/sysv/linux/kernel-features.h     |  8 +++++
>  sysdeps/unix/sysv/linux/syscalls.list         |  2 +-
>  15 files changed, 76 insertions(+), 68 deletions(-)
>  rename sysdeps/unix/sysv/linux/closefrom.c => io/close_range.c (59%)
>  rename {sysdeps/unix/sysv/linux => io}/tst-close_range.c (98%)
>  delete mode 100644 sysdeps/mach/hurd/closefrom.c
> 
> diff --git a/include/unistd.h b/include/unistd.h
> index 7849562c42..927d249380 100644
> --- a/include/unistd.h
> +++ b/include/unistd.h
> @@ -3,6 +3,9 @@
>  
>  # ifndef _ISOMAC
>  
> +#  include <stdbool.h>
> +#  include <kernel-features.h>
> +
>  libc_hidden_proto (_exit, __noreturn__)
>  #  ifndef NO_RTLD_HIDDEN
>  rtld_hidden_proto (_exit, __noreturn__)
> @@ -158,7 +161,14 @@ extern int __brk (void *__addr) attribute_hidden;
>  extern int __close (int __fd);
>  libc_hidden_proto (__close)
>  extern int __libc_close (int __fd);
> +#if __ASSUME_CLOSE_RANGE
> +static inline _Bool __closefrom_fallback (int __lowfd, _Bool dirfd_fallback)
> +{
> +  return false;
> +}
> +#else
>  extern _Bool __closefrom_fallback (int __lowfd, _Bool) attribute_hidden;
> +#endif
>  extern ssize_t __read (int __fd, void *__buf, size_t __nbytes);
>  libc_hidden_proto (__read)
>  extern ssize_t __write (int __fd, const void *__buf, size_t __n);
> diff --git a/io/Makefile b/io/Makefile
> index ecf65aba60..83f6ffdb76 100644
> --- a/io/Makefile
> +++ b/io/Makefile
> @@ -57,7 +57,7 @@ routines :=								\
>  	utimensat futimens file_change_detection			\
>  	fts64-time64							\
>  	ftw64-time64							\
> -	closefrom
> +	closefrom close_range
>  
>  others		:= pwd
>  test-srcs	:= ftwtest ftwtest-time64
> @@ -79,6 +79,7 @@ tests		:= test-utime test-stat test-stat2 test-lfs tst-getcwd \
>  		   tst-futimens \
>  		   tst-utimensat \
>  		   tst-closefrom \
> +		   tst-close_range \
>  		   tst-ftw-bz28126
>  
>  tests-time64 := \
> diff --git a/sysdeps/unix/sysv/linux/closefrom.c b/io/close_range.c
> similarity index 59%
> rename from sysdeps/unix/sysv/linux/closefrom.c
> rename to io/close_range.c
> index 372896b775..26a615d8b9 100644
> --- a/sysdeps/unix/sysv/linux/closefrom.c
> +++ b/io/close_range.c
> @@ -1,4 +1,4 @@
> -/* Close a range of file descriptors.  Linux version.
> +/* Close a range of file descriptors.
>     Copyright (C) 2021 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>  
> @@ -16,21 +16,29 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <stdbool.h>
> -#include <stdio.h>
> -#include <sys/param.h>
> +#include <errno.h>
> +#include <not-cancel.h>
>  #include <unistd.h>
>  
> -void
> -__closefrom (int lowfd)
> +/* Close the file descriptors from FIRST up to LAST, inclusive.  */
> +int
> +__close_range (unsigned int first, unsigned int last,
> +	       int flags)
>  {
> -  int l = MAX (0, lowfd);
> +  if (first > last || flags != 0)
> +    {
> +      __set_errno (EINVAL);
> +      return -1;
> +    }
>  
> -  int r = __close_range (l, ~0U, 0);
> -  if (r == 0)
> -    return;
> +  int maxfd = __getdtablesize ();
> +  if (maxfd == -1)
> +    return -1;
>  
> -  if (!__closefrom_fallback (l, true))
> -    __fortify_fail ("closefrom failed to close a file descriptor");
> +  for (int i = first; i <= last && i < maxfd; i++)
> +    __close_nocancel_nostatus (i);
> +
> +  return 0;
>  }
> -weak_alias (__closefrom, closefrom)
> +libc_hidden_def (__close_range)
> +weak_alias (__close_range, close_range)
> diff --git a/io/closefrom.c b/io/closefrom.c
> index 01660a7531..e9167687bc 100644
> --- a/io/closefrom.c
> +++ b/io/closefrom.c
> @@ -16,19 +16,21 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> +#include <stdbool.h>
>  #include <stdio.h>
> +#include <sys/param.h>
>  #include <unistd.h>
> -#include <not-cancel.h>
>  
>  void
>  __closefrom (int lowfd)
>  {
> -  int maxfd = __getdtablesize ();
> -  if (maxfd == -1)
> -    __fortify_fail ("closefrom failed to get the file descriptor table size");
> +  int l = MAX (0, lowfd);
>  
> -  for (int i = 0; i < maxfd; i++)
> -    if (i >= lowfd)
> -      __close_nocancel_nostatus (i);
> +  int r = __close_range (l, ~0U, 0);
> +  if (r == 0)
> +    return ;
> +
> +  if (!__closefrom_fallback (l, true))
> +    __fortify_fail ("closefrom failed to close a file descriptor");
>  }
>  weak_alias (__closefrom, closefrom)
> diff --git a/sysdeps/unix/sysv/linux/tst-close_range.c b/io/tst-close_range.c
> similarity index 98%
> rename from sysdeps/unix/sysv/linux/tst-close_range.c
> rename to io/tst-close_range.c
> index f5069d1b8a..f05b4ff6ae 100644
> --- a/sysdeps/unix/sysv/linux/tst-close_range.c
> +++ b/io/tst-close_range.c
> @@ -119,6 +119,7 @@ close_range_test (void)
>    support_descriptors_free (descrs);
>  }
>  
> +#ifdef __linux__
>  _Noreturn static int
>  close_range_test_fn (void *arg)
>  {
> @@ -155,8 +156,10 @@ close_range_test_subprocess (void)
>    support_descriptors_check (descrs);
>    support_descriptors_free (descrs);
>  }
> +#endif
>  
>  
> +#ifdef CLOSE_RANGE_UNSHARE
>  _Noreturn static int
>  close_range_unshare_test_fn (void *arg)
>  {
> @@ -200,6 +203,7 @@ close_range_unshare_test (void)
>    support_descriptors_check (descrs1);
>    support_descriptors_free (descrs1);
>  }
> +#endif
>  
>  static bool
>  is_in_array (int *arr, size_t len, int fd)
> @@ -282,8 +286,12 @@ do_test (void)
>  {
>    close_range_test_max_upper_limit ();
>    close_range_test ();
> +#ifdef __linux__
>    close_range_test_subprocess ();
> +#endif
> +#ifdef CLOSE_RANGE_UNSHARE
>    close_range_unshare_test ();
> +#endif
>    close_range_cloexec_test ();
>  
>    return 0;
> diff --git a/posix/unistd.h b/posix/unistd.h
> index 7a61ff5e86..3c8a7ced6a 100644
> --- a/posix/unistd.h
> +++ b/posix/unistd.h
> @@ -1199,6 +1199,16 @@ int getentropy (void *__buffer, size_t __length) __wur
>      __attr_access ((__write_only__, 1, 2));
>  #endif
>  
> +#ifdef __USE_GNU
> +/* Close all file descriptors in the range FD up to MAX_FD.  The flag FLAGS
> +   are define by the CLOSE_RANGE prefix.  This function behaves like close
> +   on the range and gaps where the file descriptor is invalid or errors
> +   encountered while closing file descriptors are ignored.   Returns 0 on
> +   successor or -1 for failure (and sets errno accordingly).  */
> +extern int close_range (unsigned int __fd, unsigned int __max_fd,
> +			int __flags) __THROW;
> +#endif
> +
>  /* Define some macros helping to catch buffer overflows.  */
>  #if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function
>  # include <bits/unistd.h>
> diff --git a/sysdeps/mach/hurd/Makefile b/sysdeps/mach/hurd/Makefile
> index 9acbe80f26..17bb643c18 100644
> --- a/sysdeps/mach/hurd/Makefile
> +++ b/sysdeps/mach/hurd/Makefile
> @@ -196,7 +196,7 @@ sysdep_routines += cthreads
>  endif
>  
>  ifeq (io, $(subdir))
> -sysdep_routines += f_setlk close_nocancel close_nocancel_nostatus close_range \
> +sysdep_routines += f_setlk close_nocancel close_nocancel_nostatus \
>  		   fcntl_nocancel open_nocancel openat_nocancel read_nocancel \
>  		   pread64_nocancel write_nocancel pwrite64_nocancel \
>  		   wait4_nocancel \
> diff --git a/sysdeps/mach/hurd/bits/unistd_ext.h b/sysdeps/mach/hurd/bits/unistd_ext.h
> index 288f504a3c..14f85539d5 100644
> --- a/sysdeps/mach/hurd/bits/unistd_ext.h
> +++ b/sysdeps/mach/hurd/bits/unistd_ext.h
> @@ -25,10 +25,4 @@
>  /* Set the FD_CLOEXEC bit instead of closing the file descriptor.  */
>  #define CLOSE_RANGE_CLOEXEC (1U << 2)
>  
> -/* Close the file descriptors from FIRST up to LAST, inclusive.
> -   If CLOSE_RANGE_CLOEXEC is set in FLAGS, set the FD_CLOEXEC flag
> -   instead of closing.  */
> -extern int close_range (unsigned int __first, unsigned int __last,
> -			int __flags) __THROW;
> -
>  #endif /* __USE_GNU  */
> diff --git a/sysdeps/mach/hurd/closefrom.c b/sysdeps/mach/hurd/closefrom.c
> deleted file mode 100644
> index 5d667cf6c4..0000000000
> --- a/sysdeps/mach/hurd/closefrom.c
> +++ /dev/null
> @@ -1,29 +0,0 @@
> -/* Close a range of file descriptors.  Hurd version.
> -   Copyright (C) 2021 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 <unistd.h>
> -#include <sys/param.h>
> -
> -void
> -__closefrom (int lowfd)
> -{
> -  int l = MAX (0, lowfd);
> -
> -  (void) __close_range (l, ~0U, 0);
> -}
> -weak_alias (__closefrom, closefrom)
> diff --git a/sysdeps/mach/hurd/kernel-features.h b/sysdeps/mach/hurd/kernel-features.h
> index 7d4eaee0a6..5fd37a6d7b 100644
> --- a/sysdeps/mach/hurd/kernel-features.h
> +++ b/sysdeps/mach/hurd/kernel-features.h
> @@ -19,3 +19,5 @@
>  /* This file can define __ASSUME_* macros checked by certain source files.
>     Almost none of these are used outside of sysdeps/unix/sysv/linux code.
>     But those referring to POSIX-level features like O_* flags can be.  */
> +
> +#define __ASSUME_CLOSE_RANGE 1
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 76ad06361c..76042a6019 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -120,7 +120,6 @@ tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
>  	 tst-timerfd tst-ppoll \
>  	 tst-clock_adjtime tst-adjtimex tst-ntp_adjtime tst-ntp_gettime \
>  	 tst-ntp_gettimex tst-sigtimedwait tst-misalign-clone \
> -  tst-close_range \
>    tst-prctl \
>    tst-scm_rights \
>    # tests
> diff --git a/sysdeps/unix/sysv/linux/bits/unistd_ext.h b/sysdeps/unix/sysv/linux/bits/unistd_ext.h
> index ae9994403c..8f422e60da 100644
> --- a/sysdeps/unix/sysv/linux/bits/unistd_ext.h
> +++ b/sysdeps/unix/sysv/linux/bits/unistd_ext.h
> @@ -47,13 +47,4 @@ extern __pid_t gettid (void) __THROW;
>  # define CLOSE_RANGE_CLOEXEC (1U << 2)
>  #endif
>  
> -/* Close all file descriptors in the range FD up to MAX_FD.  The flag FLAGS
> -   are define by the CLOSE_RANGE prefix.  This function behaves like close
> -   on the range, but in a fail-safe where it will either fail and not close
> -   any file descriptor or close all of them.  Gaps where the file descriptor
> -   is invalid are ignored.   Returns 0 on successor or -1 for failure (and
> -   sets errno accordingly).  */
> -extern int close_range (unsigned int __fd, unsigned int __max_fd,
> -			int __flags) __THROW;
> -
>  #endif /* __USE_GNU  */
> diff --git a/sysdeps/unix/sysv/linux/closefrom_fallback.c b/sysdeps/unix/sysv/linux/closefrom_fallback.c
> index f215fd2c09..a377ebc544 100644
> --- a/sysdeps/unix/sysv/linux/closefrom_fallback.c
> +++ b/sysdeps/unix/sysv/linux/closefrom_fallback.c
> @@ -21,6 +21,8 @@
>  #include <not-cancel.h>
>  #include <stdbool.h>
>  
> +#if !__ASSUME_CLOSE_RANGE
> +
>  /* Fallback code: iterates over /proc/self/fd, closing each file descriptor
>     that fall on the criteria.  If DIRFD_FALLBACK is set, a failure on
>     /proc/self/fd open will trigger a fallback that tries to close a file
> @@ -97,3 +99,5 @@ err:
>    __close_nocancel (dirfd);
>    return ret;
>  }
> +
> +#endif
> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index ffb6af196b..a1108d434f 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -220,6 +220,14 @@
>  # define __ASSUME_FACCESSAT2 0
>  #endif
>  
> +/* The close_range system call was introduced across all architectures
> +   in Linux 5.8.  */
> +#if __LINUX_KERNEL_VERSION >= 0x050900
> +# define __ASSUME_CLOSE_RANGE 1
> +#else
> +# define __ASSUME_CLOSE_RANGE 0
> +#endif
> +
>  /* The FUTEX_LOCK_PI2 operation was introduced across all architectures in Linux
>     5.14.  */
>  #if __LINUX_KERNEL_VERSION >= 0x050e00
> diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
> index 29899eb264..c38dbb34a1 100644
> --- a/sysdeps/unix/sysv/linux/syscalls.list
> +++ b/sysdeps/unix/sysv/linux/syscalls.list
> @@ -99,4 +99,4 @@ pkey_alloc	EXTRA	pkey_alloc	i:ii	pkey_alloc
>  pkey_free	EXTRA	pkey_free	i:i	pkey_free
>  gettid          EXTRA   gettid          Ei:     __gettid	gettid
>  tgkill          EXTRA   tgkill          i:iii   __tgkill	tgkill
> -close_range     EXTRA   close_range     i:iii   __close_range   close_range
> +close_range     -       close_range     i:iii   __close_range   close_range
>