[Libguestfs] [nbdkit] Proposed (new) filter API
Richard W.M. Jones
rjones at redhat.com
Tue Jan 16 14:40:15 UTC 2018
Here's my second attempt at a filter API.
As before, .config and .config_complete can only call the
next->.config or next->.config_complete methods in the chain
respectively.
The change is with the connected functions (get_size, pread, pwrite,
etc.). Here we pass a struct of next functions allowing the filter to
call any functions on the plugin, so for example a write can turn into
read + write (and vice versa although that might not be a good idea).
Also .open and .close cannot be intercepted by the filter. They're
just used to allow the filter to allocate a handle.
Rich.
--
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/* nbdkit
* Copyright (C) 2013-2017 Red Hat Inc.
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*
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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*/
/* See nbdkit-filter(3) for documentation and how to write a filter. */
#ifndef NBDKIT_FILTER_H
#define NBDKIT_FILTER_H
/* This header also defines some useful functions like nbdkit_debug
* and nbdkit_parse_size which are appropriate for filters to use.
*/
#include <nbdkit-plugin.h>
#ifdef __cplusplus
extern "C" {
#endif
#define NBDKIT_FILTER_API_VERSION 1
typedef int (*nbdkit_next_config) (void *nxdata,
const char *key, const char *value);
typedef int (*nbdkit_next_config_complete) (void *nxdata);
struct nbdkit_next {
int64_t (*get_size) (void *nxdata);
int (*can_write) (void *nxdata);
int (*can_flush) (void *nxdata);
int (*is_rotational) (void *nxdata);
int (*can_trim) (void *nxdata);
int (*pread) (void *nxdata, void *buf, uint32_t count, uint64_t offset);
int (*pwrite) (void *nxdata,
const void *buf, uint32_t count, uint64_t offset);
int (*flush) (void *nxdata);
int (*trim) (void *nxdata, uint32_t count, uint64_t offset);
int (*zero) (void *nxdata, uint32_t count, uint64_t offset, int may_trim);
};
struct nbdkit_filter {
/* Do not set these fields directly; use NBDKIT_REGISTER_FILTER.
* They exist so that we can support filters compiled against
* one version of the header with a runtime compiled against a
* different version with more (or fewer) fields.
*/
uint64_t _struct_size;
int _api_version;
/* New fields will only be added at the end of the struct. */
const char *name;
const char *longname;
const char *version;
const char *description;
void (*load) (void);
void (*unload) (void);
int (*config) (nbdkit_next_config *next, void *nxdata,
const char *key, const char *value);
int (*config_complete) (nbdkit_next_config_complete *next, void *nxdata);
const char *config_help;
void * (*open) (int readonly);
void (*close) (void *handle);
int64_t (*get_size) (struct nbdkit_next *next, void *nxdata,
void *handle);
int (*can_write) (struct nbdkit_next *next, void *nxdata,
void *handle);
int (*can_flush) (struct nbdkit_next *next, void *nxdata,
void *handle);
int (*is_rotational) (struct nbdkit_next *next,
void *nxdata,
void *handle);
int (*can_trim) (struct nbdkit_next *next, void *nxdata,
void *handle);
int (*pread) (struct nbdkit_next *next, void *nxdata,
void *handle, void *buf, uint32_t count, uint64_t offset);
int (*pwrite) (struct nbdkit_next *next, void *nxdata,
void *handle,
const void *buf, uint32_t count, uint64_t offset);
int (*flush) (struct nbdkit_next *next, void *nxdata,
void *handle);
int (*trim) (struct nbdkit_next *next, void *nxdata,
void *handle, uint32_t count, uint64_t offset);
int (*zero) (struct nbdkit_next *next, void *nxdata,
void *handle, uint32_t count, uint64_t offset, int may_trim);
};
#ifndef NBDKIT_CXX_LANG_C
#ifdef __cplusplus
#define NBDKIT_CXX_LANG_C extern "C"
#else
#define NBDKIT_CXX_LANG_C /* nothing */
#endif
#endif
#define NBDKIT_REGISTER_FILTER(filter) \
NBDKIT_CXX_LANG_C \
struct nbdkit_filter * \
filter_init (void) \
{ \
(filter)._struct_size = sizeof (filter); \
(filter)._api_version = NBDKIT_API_VERSION; \
return &(filter); \
}
#ifdef __cplusplus
}
#endif
#endif /* NBDKIT_FILTER_H */
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