On 05/07/2017 16:01, Anton Nefedov wrote: > This patch adds a possibility to change a char device without a frontend > removal. > > 1. Ideally, it would have to happen transparently to a frontend, i.e. > frontend would continue its regular operation. > However, backends are not stateless and are set up by the frontends > via qemu_chr_fe_<> functions, and it's not (generally) possible to replay > that setup entirely in a backend code, as different chardevs respond > to the setup calls differently, so do frontends work differently basing > on those setup responses. > Moreover, some frontend can generally get and save the backend pointer > (qemu_chr_fe_get_driver()), and it will become invalid after backend change. > > So, a frontend which would like to support chardev hotswap has to register > a "backend change" handler, and redo its backend setup there. > > 2. Write path can be used by multiple threads and thus protected with > chr_write_lock. > So hotswap also has to be protected so write functions won't access > a backend being replaced.
Does this matter in practice? CharBackend thread safety can be left to the front-end. Paolo
