=head1 NAME

nbd_set_debug_callback - set the debug callback

=head1 SYNOPSIS

 #include <libnbd.h>

 typedef struct {
   int (*callback) (void *user_data, const char *context,
                    const char *msg);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_debug_callback;

 int nbd_set_debug_callback (
       struct nbd_handle *h,
       nbd_debug_callback debug_callback
     );

=head1 DESCRIPTION

Set the debug callback.
This function is called when the library
emits debug messages, when debugging is enabled on a handle.  The
callback parameters are C<user_data> passed to this function, the
name of the libnbd function emitting the debug message (C<context>),
and the message itself (C<msg>).  If no debug callback is set on
a handle then messages are printed on C<stderr>.

The callback should not call C<nbd_*> APIs on the same handle since it can
be called while holding the handle lock and will cause a deadlock.

=head1 RETURN VALUE

If the call is successful the function returns C<0>.

=head1 ERRORS

On error C<-1> is returned.

Refer to L<libnbd(3)/ERROR HANDLING>
for how to get further details of the error.

The following parameters must not be NULL: C<h>.
For more information see L<libnbd(3)/Non-NULL parameters>.

=head1 VERSION

This function first appeared in libnbd 1.0.

If you need to test if this function is available at compile time
check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_SET_DEBUG_CALLBACK 1

=head1 SEE ALSO

L<nbd_create(3)>,
L<libnbd(3)>.

=head1 AUTHORS

Eric Blake

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
