basic/xattr-util: do not cast ssize_t to int

gcc warns about unitialized memory access because it notices that ssize_t which
is < 0 could be cast to positive int value. We know that this can't really
happen because only -1 can be returned, but OTOH, in principle a large
*positive* value cannot be cast properly. This is unlikely too, since xattrs
cannot be too large, but it seems cleaner to just use a size_t to return the
value and avoid the cast altoghter. This makes the code simpler and gcc is
happy too.

The following warning goes away:
[113/1502] Compiling C object 'src/basic/basic@sta/xattr-util.c.o'.
In file included from ../src/basic/alloc-util.h:28:0,
                 from ../src/basic/xattr-util.c:30:
../src/basic/xattr-util.c: In function ‘fd_getcrtime_at’:
../src/basic/macro.h:207:60: warning: ‘b’ may be used uninitialized in this function [-Wmaybe-uninitialized]
                 UNIQ_T(A,aq) < UNIQ_T(B,bq) ? UNIQ_T(A,aq) : UNIQ_T(B,bq); \
                                                            ^
../src/basic/xattr-util.c:155:19: note: ‘b’ was declared here
         usec_t a, b;
                   ^

1 files changed, 5 insertions, 3 deletions

diff --git a/src/test/test-xattr-util.c b/src/test/test-xattr-util.c
index 17087a282d..36b6480219 100644
--- a/src/test/test-xattr-util.c
+++ b/src/test/test-xattr-util.c
@@ -36,8 +36,9 @@ static void test_fgetxattrat_fake(void) {
         char t[] = "/var/tmp/xattrtestXXXXXX";
         _cleanup_close_ int fd = -1;
         const char *x;
-        char v[3] = {};
+        char v[3];
         int r;
+        size_t size;
 
         assert_se(mkdtemp(t));
         x = strjoina(t, "/test");
@@ -51,13 +52,14 @@ static void test_fgetxattrat_fake(void) {
         fd = open(t, O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY);
         assert_se(fd >= 0);
 
-        assert_se(fgetxattrat_fake(fd, "test", "user.foo", v, 3, 0) >= 0);
+        assert_se(fgetxattrat_fake(fd, "test", "user.foo", v, 3, 0, &size) >= 0);
+        assert_se(size == 3);
         assert_se(memcmp(v, "bar", 3) == 0);
 
         safe_close(fd);
         fd = open("/", O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY);
         assert_se(fd >= 0);
-        assert_se(fgetxattrat_fake(fd, "usr", "user.idontexist", v, 3, 0) == -ENODATA);
+        assert_se(fgetxattrat_fake(fd, "usr", "user.idontexist", v, 3, 0, &size) == -ENODATA);
 
 cleanup:
         assert_se(unlink(x) >= 0);