[Qemu-block] [RFC PATCH v2 13/18] oslib-posix: Ignore fcntl("/dev/null", F_SETFL, O_NONBLOCK) failure

[Philippe Mathieu-Daudé]

Previous to OpenBSD 6.3 [1], fcntl(F_SETFL) is not permitted on
memory devices.
Trying this call sets errno to ENODEV ("not a memory device"):

  19 ENODEV Operation not supported by device.
    An attempt was made to apply an inappropriate function to a device,
    for example, trying to read a write-only device such as a printer.

Do not assert fcntl failures in this specific case (errno set to ENODEV)
on OpenBSD. This fixes:

  $ lm32-softmmu/qemu-system-lm32
  assertion "f != -1" failed: file "util/oslib-posix.c", line 247, function 
"qemu_set_nonblock"
  Abort trap (core dumped)

[1] The fix seems https://github.com/openbsd/src/commit/c2a35b387f9d3c
  "fcntl(F_SETFL) invokes the FIONBIO and FIOASYNC ioctls internally, so
  the memory devices (/dev/null, /dev/zero, etc) need to permit them."

Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
---
 util/oslib-posix.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 4ce1ba9ca4..2f0f27e6d9 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -244,7 +244,17 @@ void qemu_set_nonblock(int fd)
     f = fcntl(fd, F_GETFL);
     assert(f != -1);
     f = fcntl(fd, F_SETFL, f | O_NONBLOCK);
+#ifdef __OpenBSD__
+    if (f == -1) {
+        /*
+         * Previous to OpenBSD 6.3, fcntl(F_SETFL) is not permitted on
+         * memory devices and sets errno to ENODEV.
+         */
+        assert(errno == ENODEV);
+    }
+#else
     assert(f != -1);
+#endif
 }
 
 int socket_set_fast_reuse(int fd)
-- 
2.20.1