# SYNOPSIS
#
# AMANDA_SETUP_FILE_LOCKING
#
# OVERVIEW
#
# Set up file locking support. Four locking mechanisms are available:
# POSIX_FCNTL - use fcntl(). The full job.
# FLOCK - use flock(). Does just as well.
# LOCKF - use lockf(). Only handles advisory, exclusive,
# blocking file locks as used by Amanda.
# LNLOCK - Home brew exclusive, blocking file lock.
#
# For the chosen method, WANT_AMFLOCK_mech is defined and set up as an
# AM_CONDITIONAL. Also, LOCKING, which contains the mechanism, is substituted.
#
AC_DEFUN([AMANDA_SETUP_FILE_LOCKING],
[
AC_CHECK_HEADERS(
fcntl.h \
sys/fcntl.h \
sys/types.h \
sys/file.h \
unistd.h \
)
# find a working file-locking mechanism.
# Note: these all use AC_TRY_LINK to make sure that we can compile
# and link each variant. They do not try to test the variants --
# that is left to runtime.
LOCKING="no"
# check POSIX locking
AC_CACHE_CHECK(
[whether POSIX locking (with fcntl(2)) is available],
amanda_cv_posix_filelocking,
[
AC_TRY_LINK([
#if HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
#if HAVE_FCNTL_H
# include <fcntl.h>
#endif
], [
struct flock lock;
lock.l_type = F_RDLCK;
lock.l_start = 0;
lock.l_whence = SEEK_CUR;
lock.l_len = 0;
return fcntl(1, F_SETLK, &lock);
], [
amanda_cv_posix_filelocking="yes"
],[
amanda_cv_posix_filelocking="no"
])
])
if test "x$amanda_cv_posix_filelocking" = xyes; then
AC_DEFINE(WANT_AMFLOCK_POSIX,1,[Define to use POSIX (fcntl()) for file locking])
WANT_AMFLOCK_POSIX="yes"
LOCKING="POSIX_FCNTL"
fi
AM_CONDITIONAL(WANT_AMFLOCK_POSIX, test x"$WANT_AMFLOCK_POSIX" = x"yes")
# check flock-based (BSD) locking
AC_CACHE_CHECK(
[whether flock locking is available],
amanda_cv_flock_filelocking,
[
AC_TRY_LINK([
#if HAVE_SYS_FILE_H
# include <sys/file.h>
#endif
], [
return flock(1, LOCK_SH);
], [
amanda_cv_flock_filelocking="yes"
],[
amanda_cv_flock_filelocking="no"
])
])
if test "x$amanda_cv_flock_filelocking" = xyes; then
AC_DEFINE(WANT_AMFLOCK_FLOCK,1,[Define to use flock(2) for file locking])
WANT_AMFLOCK_FLOCK="yes"
LOCKING="FLOCK"
fi
AM_CONDITIONAL(WANT_AMFLOCK_FLOCK, test x"$WANT_AMFLOCK_FLOCK" = x"yes")
# check lockf-based (SVR2, SVR3, SVR4) locking
AC_CACHE_CHECK(
[whether lockf(3) locking is available],
amanda_cv_lockf_filelocking,
[
AC_TRY_LINK([
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
], [
return lockf(1, F_LOCK, 0);
], [
amanda_cv_lockf_filelocking="yes"
],[
amanda_cv_lockf_filelocking="no"
])
])
if test "x$amanda_cv_lockf_filelocking" = xyes; then
AC_DEFINE(WANT_AMFLOCK_LOCKF,1,[Define to use lockf(3) for file locking.])
WANT_AMFLOCK_LOCKF="yes"
LOCKING="LOCKF"
fi
AM_CONDITIONAL(WANT_AMFLOCK_LOCKF, test x"$WANT_AMFLOCK_LOCKF" = x"yes")
# check our homebrew hardlink-based locking (requires hardlinks)
AC_CACHE_CHECK(
[whether link(2) is available for locking],
amanda_cv_lnlock_filelocking,
[
AC_TRY_LINK([
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
], [
return link("/tmp/foo", "/tmp/bar");
], [
amanda_cv_lnlock_filelocking="yes"
],[
amanda_cv_lnlock_filelocking="no"
])
])
if test "x$amanda_cv_lnlock_filelocking" = xyes; then
AC_DEFINE(WANT_AMFLOCK_LNLOCK,1,[Define to use link(2) to emulate file locking.])
WANT_AMFLOCK_LNLOCK="yes"
LOCKING="LNLOCK"
fi
AM_CONDITIONAL(WANT_AMFLOCK_LNLOCK, test x"$WANT_AMFLOCK_LNLOCK" = x"yes")
if test x"$LOCKING" = "no"; then
# this shouldn't happen, and is *bad* if it does
AC_MSG_ERROR([*** No working file locking capability found!])
fi
AC_SUBST(LOCKING)
])