lib/copy-file-range.c

   1 /* Stub for copy_file_range
   2    Copyright 2019-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 #include <unistd.h>
  20
  21 #include <errno.h>
  22
  23 #if defined __linux__ && HAVE_COPY_FILE_RANGE
  24 # include <sys/utsname.h>
  25 #endif
  26
  27 ssize_t
  28 copy_file_range (int infd, off_t *pinoff,
  29                  int outfd, off_t *poutoff,
  30                  size_t length, unsigned int flags)
  31 {
  32 #undef copy_file_range
  33
  34 #if defined __linux__ && HAVE_COPY_FILE_RANGE
  35   /* The implementation of copy_file_range (which first appeared in
  36      Linux kernel release 4.5) had many issues before release 5.3
  37      <https://lwn.net/Articles/789527/>, so fail with ENOSYS for Linux
  38      kernels 5.2 and earlier.
  39
  40      This workaround, and the configure-time check for Linux, can be
  41      removed when such kernels (released March 2016 through September
  42      2019) are no longer a consideration.  As of January 2021, the
  43      furthest-future planned kernel EOL is December 2024 for kernel
  44      release 4.19.  */
  45
  46     static signed char ok;
  47
  48     if (! ok)
  49       {
  50         struct utsname name;
  51         uname (&name);
  52         char *p = name.release;
  53         ok = ((p[1] != '.' || '5' < p[0]
  54                || (p[0] == '5' && (p[3] != '.' || '2' < p[2])))
  55               ? 1 : -1);
  56       }
  57
  58     if (0 < ok)
  59       return copy_file_range (infd, pinoff, outfd, poutoff, length, flags);
  60 #endif
  61
  62   /* There is little need to emulate copy_file_range with read+write,
  63      since programs that use copy_file_range must fall back on
  64      read+write anyway.  */
  65   errno = ENOSYS;
  66   return -1;
  67 }