Add glnx_fd_close() and glnx_autofd

I'd like to have the checks for `EBADF` as well as the
"assign to -1" in more places.  The cleanup function we
had for `glnx_fd_close` is actually what we want.

Let's rename the cleanup macro to `glnx_autofd` to better match
other autocleanups like `g_autofree`.

Then we can use `glnx_fd_close()` as a replacement for plain Unix `close()`. I
left the `glnx_close_fd` macro, but it's obviously confusing now with the
former. We'll eventually remove it.

glnx-dirfd.c

@@ -382,8 +382,7 @@ _glnx_tmpdir_free (GLnxTmpDir *tmpd,
   if (!(tmpd && tmpd->initialized))
     return TRUE;
   g_assert_cmpint (tmpd->fd, !=, -1);
-  (void) close (tmpd->fd);
-  tmpd->fd = -1;
+  glnx_close_fd (&tmpd->fd);
   g_assert (tmpd->path);
   g_assert_cmpint (tmpd->src_dfd, !=, -1);
   g_autofree char *path = tmpd->path; /* Take ownership */

glnx-local-alloc.h

@@ -42,14 +42,30 @@ glnx_local_obj_unref (void *v)
 }
 #define glnx_unref_object __attribute__ ((cleanup(glnx_local_obj_unref)))
 
-static inline void
-glnx_cleanup_close_fdp (int *fdp)
+static inline int
+glnx_steal_fd (int *fdp)
 {
-  int fd, errsv;
+  int fd = *fdp;
+  *fdp = -1;
+  return fd;
+}
+
+/**
+ * glnx_close_fd:
+ * @fdp: Pointer to fd
+ *
+ * Effectively `close (glnx_steal_fd (&fd))`.  Also
+ * asserts that `close()` did not raise `EBADF` - encountering
+ * that error is usually a critical bug in the program.
+ */
+static inline void
+glnx_close_fd (int *fdp)
+{
+  int errsv;
 
   g_assert (fdp);
 
-  fd = *fdp;
+  int fd = glnx_steal_fd (fdp);
   if (fd >= 0)
     {
       errsv = errno;
@@ -62,16 +78,14 @@ glnx_cleanup_close_fdp (int *fdp)
 /**
  * glnx_fd_close:
  *
+ * Deprecated in favor of `glnx_autofd`.
+ */
+#define glnx_fd_close __attribute__((cleanup(glnx_close_fd)))
+/**
+ * glnx_autofd:
+ *
  * Call close() on a variable location when it goes out of scope.
  */
-#define glnx_fd_close __attribute__((cleanup(glnx_cleanup_close_fdp)))
-
-static inline int
-glnx_steal_fd (int *fdp)
-{
-  int fd = *fdp;
-  *fdp = -1;
-  return fd;
-}
+#define glnx_autofd __attribute__((cleanup(glnx_close_fd)))
 
 G_END_DECLS

glnx-lockfile.c

@@ -119,8 +119,7 @@ glnx_make_lock_file(int dfd, const char *p, int operation, GLnxLockFile *out_loc
                 if (st.st_nlink > 0)
                         break;
 
-                (void) close(fd);
-                fd = -1;
+                glnx_close_fd (&fd);
         }
 
         /* Note that if this is not AT_FDCWD, the caller takes responsibility
@@ -174,9 +173,7 @@ void glnx_release_lock_file(GLnxLockFile *f) {
                 f->path = NULL;
         }
 
-        if (f->fd != -1)
-                (void) close (f->fd);
-        f->fd = -1;
+        glnx_close_fd (&f->fd);
         f->operation = 0;
         f->initialized = FALSE;
 }