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Diffstat (limited to 'm4/link-follow.m4')
| -rw-r--r-- | m4/link-follow.m4 | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/m4/link-follow.m4 b/m4/link-follow.m4 new file mode 100644 index 0000000..9ee5a02 --- /dev/null +++ b/m4/link-follow.m4 @@ -0,0 +1,110 @@ +# serial 21 +dnl Run a program to determine whether link(2) follows symlinks. +dnl Set LINK_FOLLOWS_SYMLINKS accordingly. + +# Copyright (C) 1999-2001, 2004-2006, 2009-2020 Free Software Foundation, Inc. +# This file is free software; the Free Software Foundation +# gives unlimited permission to copy and/or distribute it, +# with or without modifications, as long as this notice is preserved. + +dnl This macro can be used to emulate POSIX linkat. If +dnl LINK_FOLLOWS_SYMLINKS is 0, link matches linkat(,0), and +dnl linkat(,AT_SYMLINK_FOLLOW) requires a readlink. If it is 1, +dnl link matches linkat(,AT_SYMLINK_FOLLOW), and there is no way +dnl to do linkat(,0) on symlinks (on all other file types, +dnl link() is sufficient). If it is -1, use a Solaris specific +dnl runtime test. If it is -2, use a generic runtime test. +AC_DEFUN([gl_FUNC_LINK_FOLLOWS_SYMLINK], +[dnl + AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles + AC_CHECK_FUNCS_ONCE([readlink]) + dnl Mingw lacks link, although gnulib provides a good replacement. + dnl However, it also lacks symlink, so there's nothing to test in + dnl the first place, and no reason to need to distinguish between + dnl linkat variants. So, we set LINK_FOLLOWS_SYMLINKS to 0. + gl_link_follows_symlinks=0 # assume GNU behavior + if test $ac_cv_func_readlink = yes; then + dnl Solaris has an __xpg4 variable in libc, and it determines the + dnl behaviour of link(): It dereferences a symlink if and only if + dnl __xpg4 != 0. + AC_CACHE_CHECK([for __xpg4], [gl_cv_have___xpg4], + [AC_LINK_IFELSE( + [AC_LANG_PROGRAM( + [[extern int __xpg4;]], + [[return __xpg4;]])], + [gl_cv_have___xpg4=yes], + [gl_cv_have___xpg4=no]) + ]) + if test $gl_cv_have___xpg4 = yes; then + gl_link_follows_symlinks=-1 + else + AC_CACHE_CHECK([whether link(2) dereferences a symlink], + [gl_cv_func_link_follows_symlink], + [ + # Create a regular file. + echo > conftest.file + AC_RUN_IFELSE( + [AC_LANG_SOURCE([[ +# include <sys/types.h> +# include <sys/stat.h> +# include <unistd.h> +# include <stdlib.h> + +# define SAME_INODE(Stat_buf_1, Stat_buf_2) \ + ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \ + && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev) + + int + main () + { + const char *file = "conftest.file"; + const char *sym = "conftest.sym"; + const char *hard = "conftest.hard"; + struct stat sb_file, sb_hard; + + /* Create a symlink to the regular file. */ + if (symlink (file, sym)) + return 2; + + /* Create a hard link to that symlink. */ + if (link (sym, hard)) + return 3; + + if (lstat (hard, &sb_hard)) + return 4; + if (lstat (file, &sb_file)) + return 5; + + /* If the dev/inode of hard and file are the same, then + the link call followed the symlink. */ + return SAME_INODE (sb_hard, sb_file) ? 1 : 0; + } + ]])], + [gl_cv_func_link_follows_symlink=no], dnl GNU behavior + [gl_cv_func_link_follows_symlink=yes], dnl Followed link/compile failed + [dnl We're cross compiling. + dnl The past results are "yes" on Mac OS X, FreeBSD, NetBSD, + dnl OpenBSD, Minix, AIX, HP-UX, OSF/1, and "no" on Linux, Cygwin. + case "$host_os" in + # On glibc/Linux we know the result. + linux*-gnu* | gnu*) gl_cv_func_link_follows_symlink="guessing no" ;; + # On musl/Linux we know the result. + linux*-musl*) gl_cv_func_link_follows_symlink="guessing no" ;; + # Otherwise, we don't know. + *) gl_cv_func_link_follows_symlink=unknown ;; + esac + ]) + rm -f conftest.file conftest.sym conftest.hard + ]) + case "$gl_cv_func_link_follows_symlink" in + *yes) gl_link_follows_symlinks=1 ;; + *no) ;; # already defaulted to 0 + *) gl_link_follows_symlinks=-2 ;; + esac + fi + fi + AC_DEFINE_UNQUOTED([LINK_FOLLOWS_SYMLINKS], [$gl_link_follows_symlinks], + [Define to 1 if 'link(2)' dereferences symbolic links, 0 if it + creates hard links to symlinks, -1 if it depends on the variable __xpg4, + and -2 if unknown.]) +]) |