virFileInData: Preserve errno on error

The virFileInData() function should return to the caller if the
current position the passed file is in is a data section or a
hole (and also how long the current section is). At any rate,
upon return from this function (be it successful or not) the
original position in the file is restored. This may mess up with
errno which might have been set earlier. Save the errno into a
local variable so it can be restored for the caller's sake.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NMartin Kletzander <mkletzan@redhat.com>

src/util/virfile.c

@@ -4072,11 +4072,18 @@ virFileInData(int fd,
     ret = 0;
  cleanup:
     /* At any rate, reposition back to where we started. */
-    if (cur != (off_t) -1 &&
-        lseek(fd, cur, SEEK_SET) == (off_t) -1) {
-        virReportSystemError(errno, "%s",
-                             _("unable to restore position in file"));
-        ret = -1;
+    if (cur != (off_t) -1) {
+        int theerrno = errno;
+
+        if (lseek(fd, cur, SEEK_SET) == (off_t) -1) {
+            virReportSystemError(errno, "%s",
+                                 _("unable to restore position in file"));
+            ret = -1;
+            if (theerrno == 0)
+                theerrno = errno;
+        }
+
+        errno = theerrno;
     }
     return ret;
 }