Re: [Libguestfs] [PATCH nbdkit v2 2/3] Refactor plugin_* functions into a backend struct.
On 01/16/2018 10:32 AM, Richard W.M. Jones wrote:
Introduce the concept of a backend. Currently the only type of
backend is a plugin, and there can only be one of them. Instead of
calling functions like ‘plugin_pwrite’ you call the backend method
‘backend->pwrite (backend, ...)’.
The change is largely mechanical. I was able to remove ‘assert (dl)’
statements throughout since we can now prove they will never be
called.
Note this does not lift the restriction of one plugin per server, and
it can *never* do that because plugins can use global variables.
---
+struct backend {
+ void (*free) (struct backend *);
+ int (*thread_model) (struct backend *);
+ const char *(*name) (struct backend *);
+ void (*usage) (struct backend *);
+ const char *(*version) (struct backend *);
+ void (*dump_fields) (struct backend *);
+ void (*config) (struct backend *, const char *key, const char *value);
+ void (*config_complete) (struct backend *);
+ int (*errno_is_preserved) (struct backend *);
+ int (*open) (struct backend *, struct connection *conn, int readonly);
Is it worth using 'bool' instead of 'int' where we are really using a
truth value? We can't change the nbdkit-plugin.h API (well, at least
not without plugins opting in), but the new stuff (including filters)
could be sane from the get-go instead of overloading int.
+ void (*close) (struct backend *, struct connection *conn);
+ int64_t (*get_size) (struct backend *, struct connection *conn);
+ int (*can_write) (struct backend *, struct connection *conn);
However, functions like this still need to return int because they are
tri-state (true, false, or -1 for error).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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