[PATCH v2 1/3] util: validate whether O_DIRECT is supported after failure

["Daniel P. Berrangé" <berrange@redhat.com>]

Currently we suggest that a filesystem may not support O_DIRECT after
seeing an EINVAL. Other things can cause EINVAL though, so it is better
to do an explicit check, and then report a definitive error message.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 util/osdep.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/util/osdep.c b/util/osdep.c
index 4829c07ff6..e2b7507ee2 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -332,9 +332,11 @@ int qemu_open(const char *name, int flags, ...)
     }
 
 #ifdef O_CLOEXEC
-    ret = open(name, flags | O_CLOEXEC, mode);
-#else
+    flags |= O_CLOEXEC;
+#endif
     ret = open(name, flags, mode);
+
+#ifndef O_CLOEXEC
     if (ret >= 0) {
         qemu_set_cloexec(ret);
     }
@@ -342,8 +344,13 @@ int qemu_open(const char *name, int flags, ...)
 
 #ifdef O_DIRECT
     if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
-        error_report("file system may not support O_DIRECT");
-        errno = EINVAL; /* in case it was clobbered */
+        int newflags = flags & ~O_DIRECT;
+        ret = open(name, newflags, mode);
+        if (ret != -1) {
+            close(ret);
+            error_report("file system does not support O_DIRECT");
+            errno = EINVAL;
+        }
     }
 #endif /* O_DIRECT */
 
-- 
2.26.2