[Libguestfs] [nbdkit PATCH v3 11/16] filters: Use context rather than connection to track c_next

[Eric Blake]

On 3/5/21 5:31 PM, Eric Blake wrote:
> This is another API/ABI change to filters, but that doesn't matter.
> Instead of having a 1:1 correspondence of automatic backend context to
> the current connection (which means filters.c has to consult GET_CONN
> on every action), switch things so that a given context tracks the
> next context.  This requires another signature change to the internal
> backend_open and backend_reopen functions, as well as a public change
> to the type of the argument handed to filter .open calls.  A given
> connection now only needs to track the top_context, and we no longer
> need get_context()/set_context().  Internally, nbdkit_context and
> nbdkit_next are the same type, but the public interface for filters
> keeps them separate for type-safety reasons (assigning a backend
> handle to the current filter's context is different than calling into
> the backend via next_ops/nxdata as the backend's context).
> 

> @@ -471,7 +471,7 @@ outer filter to the plugin will be in reverse.  Skipping a call to
>  C<next> is acceptable if the filter will not access C<next_ops>
>  during any of the remaining callbacks reached on the same connection.
> 
> -The value of C<backend> in this call has a lifetime that lasts until
> +The value of C<context> in this call has a lifetime that lasts until
>  the counterpart C<.close>, and it is this value (and not the distinct
>  C<nxdata> of C<.pread> and friends) that must be passed as the first
>  parameter to C<nbdkit_backend_reopen> by a filter attempting to retry
> @@ -481,14 +481,14 @@ a connection into the backend.
> 
>  Filters have access to a function for reopening the backend:
> 
> -  int (nbdkit_backend *backend, int readonly, const char *exportname,
> +  int (nbdkit_context *context, int readonly, const char *exportname,
>         void **nxdata);

This goes away in a later patch, but I might as well spell it correctly
in the earlier patches: s/int /int nbdkit_backend_reopen)/

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org