fd-util: be more careful with fclose() errnos

This might fix #15859, a bug which I find very puzzling.

(cherry picked from commit 75f6d5d87e950f62baced48fe9b58828969e3811)

diff --git a/src/basic/fd-util.c b/src/basic/fd-util.c
index 4be876e24c8bd7452bba4cdacc1161d15ff26dca..de3f238d33556948dbf3bd4f6bb94c136e12a2d7 100644 (file)
--- a/src/basic/fd-util.c
+++ b/src/basic/fd-util.c
@@ -102,13 +102,16 @@ int fclose_nointr(FILE *f) {
 
         /* Same as close_nointr(), but for fclose() */
 
+        errno = 0; /* Extra safety: if the FILE* object is not encapsulating an fd, it might not set errno
+                    * correctly. Let's hence initialize it to zero first, so that we aren't confused by any
+                    * prior errno here */
         if (fclose(f) == 0)
                 return 0;
 
         if (errno == EINTR)
                 return 0;
 
-        return -errno;
+        return errno_or_else(EIO);
 }
 
 FILE* safe_fclose(FILE *f) {