[PATCH iproute2-next v2] lib/fs: fix issue when {name,open}_to_handle_at() is not implemented

[Heiko Thiery]

With commit d5e6ee0dac64b64e the usage of functions name_to_handle_at() and
open_by_handle_at() are introduced. But these function are not available
e.g. in uclibc-ng < 1.0.35. To have a backward compatibility check for the
availability in the configure script and in case of absence do a direct
syscall.

Signed-off-by: Heiko Thiery <heiko.thiery@xxxxxxxxx>
---
v2:
 - small correction to subject
 - removed IP_CONFIG_HANDLE_AT:=y option since it is not required
 - fix indentation in check function
 - removed empty lines (thanks to Petr Vorel)
 - add #define _GNU_SOURCE in check (thanks to Petr Vorel)
 - check only for name_to_handle_at (thanks to Peter Vorel)

 configure | 28 ++++++++++++++++++++++++++++
 lib/fs.c  | 21 +++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/configure b/configure
index 2c363d3b..179eae08 100755
--- a/configure
+++ b/configure
@@ -202,6 +202,31 @@ EOF
     rm -f $TMPDIR/setnstest.c $TMPDIR/setnstest
 }
 
+check_name_to_handle_at()
+{
+    cat >$TMPDIR/name_to_handle_at_test.c <<EOF
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+int main(int argc, char **argv)
+{
+	struct file_handle *fhp;
+	int mount_id, flags, dirfd;
+	char *pathname;
+	name_to_handle_at(dirfd, pathname, fhp, &mount_id, flags);
+	return 0;
+}
+EOF
+    if $CC -I$INCLUDE -o $TMPDIR/name_to_handle_at_test $TMPDIR/name_to_handle_at_test.c >/dev/null 2>&1; then
+        echo "yes"
+        echo "CFLAGS += -DHAVE_HANDLE_AT" >>$CONFIG
+    else
+        echo "no"
+    fi
+    rm -f $TMPDIR/name_to_handle_at_test.c $TMPDIR/name_to_handle_at_test
+}
+
 check_ipset()
 {
     cat >$TMPDIR/ipsettest.c <<EOF
@@ -492,6 +517,9 @@ fi
 echo -n "libc has setns: "
 check_setns
 
+echo -n "libc has name_to_handle_at: "
+check_name_to_handle_at
+
 echo -n "SELinux support: "
 check_selinux
 
diff --git a/lib/fs.c b/lib/fs.c
index ee0b130b..feb12864 100644
--- a/lib/fs.c
+++ b/lib/fs.c
@@ -30,6 +30,27 @@
 /* if not already mounted cgroup2 is mounted here for iproute2's use */
 #define MNT_CGRP2_PATH  "/var/run/cgroup2"
 
+
+#ifndef defined HAVE_HANDLE_AT
+struct file_handle {
+	unsigned handle_bytes;
+	int handle_type;
+	unsigned char f_handle[];
+};
+
+int name_to_handle_at(int dirfd, const char *pathname,
+	struct file_handle *handle, int *mount_id, int flags)
+{
+	return syscall(name_to_handle_at, 5, dirfd, pathname, handle,
+	               mount_id, flags);
+}
+
+int open_by_handle_at(int mount_fd, struct file_handle *handle, int flags)
+{
+	return syscall(open_by_handle_at, 3, mount_fd, handle, flags);
+}
+#endif
+
 /* return mount path of first occurrence of given fstype */
 static char *find_fs_mount(const char *fs_to_find)
 {
-- 
2.30.0