libssh2_channel_set_blocking man page
libssh2_channel_set_blocking — set or clear blocking mode on channel
void libssh2_channel_set_blocking(LIBSSH2_CHANNEL *channel, int blocking);
channel - channel stream to set or clean blocking status on.
blocking - Set to a non-zero value to make the channel block, or zero to make it non-blocking.
Currently this is just a short cut call to libssh2_session_set_blocking(3) and therefore will affect the session and all channels.
libssh2_session_set_blocking(3) libssh2_channel_read_ex(3) libssh2_channel_write_ex(3)