[Libguestfs] [PATCH libnbd 2/2] generator: Print a better error message if connect(2) returns EAGAIN.

[Martin Kletzander]

On Thu, Feb 04, 2021 at 06:10:50PM +0000, Richard W.M. Jones wrote:
>The new error message is:
>
>nbd_connect_unix: connect: server backlog overflowed, see https://bugzilla.redhat.com/1925045: Resource temporarily unavailable
>
>Fixes: https://bugzilla.redhat.com/1925045
>---
> generator/states-connect.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
>diff --git a/generator/states-connect.c b/generator/states-connect.c
>index 03b34c7..98c26e5 100644
>--- a/generator/states-connect.c
>+++ b/generator/states-connect.c
>@@ -70,6 +70,22 @@ STATE_MACHINE {
>   if (r == 0 || (r == -1 && errno == EINPROGRESS))
>     return 0;
>   assert (r == -1);
>+#ifdef __linux__
>+  if (errno == EAGAIN && family == AF_UNIX) {
>+    /* This can happen on Linux when connecting to a Unix domain
>+     * socket, if the server's backlog is full.  Unfortunately there
>+     * is nothing good we can do on the client side when this happens
>+     * since any solution would involve sleeping or busy-waiting.  The

Also thanks to the passthrough of the errno any retry procedure can be done in
the client that uses libnbd.  So for both patches:

Reviewed-by: Martin Kletzander <mkletzan at redhat.com>

>+     * only solution is on the server side, increasing the backlog.
>+     * But at least improve the error message.
>+     * https://bugzilla.redhat.com/1925045
>+     */
>+    SET_NEXT_STATE (%.DEAD);
>+    set_error (errno, "connect: server backlog overflowed, "
>+               "see https://bugzilla.redhat.com/1925045");
>+    return 0;
>+  }
>+#endif
>   SET_NEXT_STATE (%.DEAD);
>   set_error (errno, "connect");
>   return 0;
>-- 
>2.29.0.rc2
>
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