[Libguestfs] [PATCH nbdkit INCOMPLETE 2/6] Introduce filters.

Filters can be placed in front of plugins to modify their behaviour. This commit introduces the <nbdkit-filter.h> header file, the manual page, the ‘filterdir’ directory (like ‘plugindir’), and the ‘filters/’ source directory which will contain both example and real filters. --- Makefile.am | 2 +- TODO | 17 +- configure.ac | 3 +- docs/Makefile.am | 9 +- docs/nbdkit-filter.pod | 478 ++++++++++++++++++++++++++++++++++++++++++++++++ docs/nbdkit-plugin.pod | 3 +- docs/nbdkit.pod | 3 +- filters/Makefile.am | 33 ++++ include/Makefile.am | 4 +- include/nbdkit-filter.h | 132 +++++++++++++ include/nbdkit-plugin.h | 2 + src/Makefile.am | 5 +- src/main.c | 1 + src/nbdkit.pc.in | 1 + 14 files changed, 671 insertions(+), 22 deletions(-) diff --git a/Makefile.am b/Makefile.am index f3c88b0..9c5b4c3 100644 --- a/Makefile.am +++ b/Makefile.am @@ -49,7 +49,7 @@ SUBDIRS = \ src if HAVE_PLUGINS -SUBDIRS += plugins +SUBDIRS += plugins filters endif SUBDIRS += tests diff --git a/TODO b/TODO index 0c027e2..0955db7 100644 --- a/TODO +++ b/TODO @@ -34,10 +34,8 @@ nbdkit there is no compelling reason unless the result is better than qemu-nbd. For the majority of users it would be better if they were directed to qemu-nbd for these use cases. -Filters -------- - -It should be possible to layer filters over plugins to do things like: +Suggestions for filters +----------------------- * adding artificial delays (see wdelay/rdelay options in the file plugin) @@ -50,17 +48,6 @@ It should be possible to layer filters over plugins to do things like: * export a single partition (like qemu-nbd -P) -A possible syntax would be: - - nbdkit --filter=delay [--filter=...] file file=foo wdelay=10 - -The filter(s) intercept all plugin calls and can either return, return -an error, or pass the call down to the next layer in the stack (and -eventually to the plugin). By intercepting the .config call the -filter can process its own parameters from the command line (wdelay=10 -in the example above), and by intercepting the .pread, .pwrite methods -the filter could inject the delaying behaviour. - Composing nbdkit ---------------- diff --git a/configure.ac b/configure.ac index a2950f6..7032614 100644 --- a/configure.ac +++ b/configure.ac @@ -181,7 +181,7 @@ AS_IF([test "x$POD2MAN" != "xno"],[ AM_CONDITIONAL([HAVE_POD2MAN], [test "x$POD2MAN" != "xno"]) AC_ARG_ENABLE([plugins], - [AS_HELP_STRING([--disable-plugins], [disable all bundled plugins])]) + [AS_HELP_STRING([--disable-plugins], [disable all bundled plugins and filters])]) AM_CONDITIONAL([HAVE_PLUGINS], [test "x$enable_plugins" != "xno"]) dnl Check for Perl, for embedding in the perl plugin. @@ -512,6 +512,7 @@ AC_CONFIG_FILES([Makefile plugins/tar/Makefile plugins/vddk/Makefile plugins/xz/Makefile + filters/Makefile src/Makefile src/nbdkit.pc tests/Makefile]) diff --git a/docs/Makefile.am b/docs/Makefile.am index 323f48d..d2330fb 100644 --- a/docs/Makefile.am +++ b/docs/Makefile.am @@ -33,6 +33,7 @@ EXTRA_DIST = \ nbdkit.pod \ nbdkit-plugin.pod + nbdkit-filter.pod CLEANFILES = *~ @@ -40,7 +41,8 @@ if HAVE_POD2MAN man_MANS = \ nbdkit.1 \ - nbdkit-plugin.3 + nbdkit-plugin.3 \ + nbdkit-filter.3 CLEANFILES += $(man_MANS) nbdkit.1: nbdkit.pod @@ -53,4 +55,9 @@ nbdkit-plugin.3: nbdkit-plugin.pod if grep 'POD ERROR' $@.t; then rm $@.t; exit 1; fi && \ mv $@.t $@ +nbdkit-filter.3: nbdkit-filter.pod + $(POD2MAN) $(POD2MAN_ARGS) --section=3 --name=nbdkit-filter $< $@.t && \ + if grep 'POD ERROR' $@.t; then rm $@.t; exit 1; fi && \ + mv $@.t $@ + endif diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod new file mode 100644 index 0000000..5fcd5ed --- /dev/null +++ b/docs/nbdkit-filter.pod @@ -0,0 +1,478 @@ +=encoding utf8 + +=head1 NAME + +nbdkit-filter - How to write nbdkit filters + +=head1 SYNOPSIS + + #include <nbdkit-filter.h> + + static int + myfilter_config (const char *key, const char *value, + int (*next) (...), void *data) + { + if (strcmp (key, "myparameter") == 0) { + // ... + return 0; + } + else { + // pass through to next filter or plugin + return next (data, key, value); + } + } + + static struct nbdkit_filter filter = { + .name = "filter", + .config = myfilter_config, + /* etc */ + }; + + NBDKIT_REGISTER_FILTER(filter) + +When this has been compiled to a shared library, do: + + nbdkit [--args ...] --filter=./myfilter.so plugin [key=value ...] + +When debugging, use the I<-fv> options: + + nbdkit -fv --filter=./myfilter.so plugin [key=value ...] + +=head1 DESCRIPTION + +One or more nbdkit filters can be placed in front of an nbdkit plugin +to modify the behaviour of the plugin. This manual page describes how +to create an nbdkit filter. + +Filters can be used for example to limit requests to an offset/limit, +add copy-on-write support, or inject delays or errors (for testing). + +Different filters can be stacked: + + NBD ┌─────────┐ ┌─────────┐ ┌────────┐ + client ───▶│ filter1 │───▶│ filter2 │── ─ ─ ──▶│ plugin │ + request └─────────┘ └─────────┘ └────────┘ + +Each filter intercepts plugin functions (see L<nbdkit-plugin(3)>) and +can modify parameters, call the following function in the chain +before, in the middle or after, or even short-cut the chain. As an +example, to process its own parameters the filter can intercept the +C<.config> method: + + static int + myfilter_config (const char *key, const char *value, + int (*next) (...), void *data) + { + if (strcmp (key, "myparameter") == 0) { + // ... + // here you would handle this key, value + // ... + return 0; + } + else { + // pass through to next filter or plugin + return next (data, key, value); + } + } + + static struct nbdkit_filter filter = { + // ... + .config = myfilter_config, + // ... + }; + +The call to C<next (data, ...)> calls the next filter or plugin in the +chain. In the example above any instances of C<myparameter=...> on +the command line would not be seen by the plugin. + +To see example filters, take a look at the source of nbdkit, in the +C<filters> directory. + +Filters must be written in C and must be fully thread safe. + +=head1 C<nbdkit-filter.h> + +All filters should start by including this header file: + + #include <nbdkit-filter.h> + +=head1 C<struct nbdkit_filter> + +All filters must define and register one C<struct nbdkit_filter>, +which contains the name of the filter and pointers to plugin methods +that the filter wants to intercept. + + static struct nbdkit_filter filter = { + .name = "filter", + .longname = "My Filter", + .description = "This is my great filter for nbdkit", + .config = myfilter_config, + /* etc */ + }; + + NBDKIT_REGISTER_FILTER(filter) + +The C<.name> field is the name of the filter. This is the only field +which is required. + +=head1 CALLBACKS + +C<struct nbdkit_filter> has some static fields describing the filter +and optional callback functions which can be used to intercept plugin +methods. + +The functions have extra C<next> and C<data> parameters which are used +to call the next filter or plugin in the chain. Note that if your +filter registers a callback but in that callback it doesn't call the +C<next> function then the corresponding method in the plugin will +never be called. + +You can modify parameters when you call the C<next> function. However +be careful when modifying strings because for some methods +(eg. C<.config>) the plugin may save the string pointer that you pass +along. So you may have to ensure that the string is not freed for the +lifetime of the server. + +=head2 C<.name> + + const char *name; + +This field (a string) is required, and B<must> contain only ASCII +alphanumeric characters and be unique amongst all filters. + +=head2 C<.version> + + const char *version; + +Filters may optionally set a version string which is displayed in help +and debugging output. + +=head2 C<.longname> + + const char *longname; + +An optional free text name of the filter. This field is used in error +messages. + +=head2 C<.description> + + const char *description; + +An optional multi-line description of the filter. + +=head2 C<.load> + + void load (void); + +This is called once just after the filter is loaded into memory. You +can use this to perform any global initialization needed by the +filter. + +=head2 C<.unload> + + void unload (void); + +This may be called once just before the filter is unloaded from +memory. Note that it's not guaranteed that C<.unload> will always be +called (eg. the server might be killed or segfault), so you should try +to make the filter as robust as possible by not requiring cleanup. +See also L<nbdkit-plugin(3)/SHUTDOWN>. + +=head2 C<.config> + + int config (const char *key, const char *value, + int (*next) (void *data, const char *key, const char *value), + void *data); + +This intercepts the plugin C<.config> method and can be used by the +filter to parse its own command line parameters. You should try to +make sure that command line parameter keys that the filter uses do not +conflict with ones that could be used by a plugin. + +If there is an error, C<.config_complete> should call C<nbdkit_error> +with an error message and return C<-1>. + +=head2 C<.config_complete> + + int config_complete (int (*next) (void *data), void *data); + +This intercepts the plugin C<.config_complete> method and can be used +to ensure that all parameters needed by the filter were supplied on +the command line. + +If there is an error, C<.config_complete> should call C<nbdkit_error> +with an error message and return C<-1>. + +=head2 C<.config_help> + + const char *config_help; + +This optional multi-line help message should summarize any +C<key=value> parameters that it takes. It does I<not> need to repeat +what already appears in C<.description>. + +If the filter doesn't take any config parameters you should probably +omit this. + +=head2 C<.open> + + void *open (int readonly, + int (*next) (void *data, int readonly), void *data); + +This intercepts the plugin C<.open> method and can be used to allocate +per-connection data structures needed by the filter. The handle +(which is not the same as the plugin handle) is passed back to other +filter callbacks and could be freed in the C<.close> callback. + +Note that the handle is completely opaque to nbdkit, but it must not +be NULL. + +Unlike other callbacks, you should I<not> call C<return next (...)> +in this callback. Instead you should check for errors by doing: + + if (next (data, readonly) == -1) { + // error from plugin .open method + // next() already called nbdkit_error so just return NULL + return NULL; + } + // no error + return my_handle; + +If there is an error, C<.open> should call C<nbdkit_error> with an +error message and return C<NULL>. + +=head2 C<.close> + + void close (void *handle, + void (*next) (void *data), void *data); + +This intercepts the plugin C<.close> method + +This is called when the client closes the connection. It should clean +up any per-connection resources used by the filter. + +=head2 C<.get_size> + + int64_t get_size (void *handle, + int64_t (*next) (void *data), void *data); + +This intercepts the plugin C<.get_size> method and can be used to read +or modify the apparent size of the block device that the NBD client +will see. + +The returned size must be E<ge> 0. If there is an error, C<.get_size> +should call C<nbdkit_error> with an error message and return C<-1>. + +=head2 C<.can_write> + +=head2 C<.can_flush> + +=head2 C<.is_rotational> + +=head2 C<.can_trim> + + int can_write (void *handle, + int (*next) (void *data), void *data); + + int can_flush (void *handle, + int (*next) (void *data), void *data); + + int is_rotational (void *handle, + int (*next) (void *data), void *data); + + int can_trim (void *handle, + int (*next) (void *data), void *data); + +These intercept the corresponding plugin methods. + +If there is an error, the callback should call C<nbdkit_error> with an +error message and return C<-1>. + +=head2 C<.pread> + + int pread (void *handle, void *buf, uint32_t count, uint64_t offset, + int (*next) (void *data, + void *buf, uint32_t count, uint64_t offset), + void *data); + +This intercepts the plugin C<.pread> method and can be used to read or +modify data read by the plugin. + +If there is an error (including a short read which couldn't be +recovered from), C<.pread> should call C<nbdkit_error> with an error +message B<and> set C<errno>, then return C<-1>. + +=head2 C<.pwrite> + + int pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset, + int (*next) (void *data, + const void *buf, uint32_t count, uint64_t offset), + void *data); + +This intercepts the plugin C<.pwrite> method and can be used to modify +data written by the plugin. + +If there is an error (including a short write which couldn't be +recovered from), C<.pwrite> should call C<nbdkit_error> with an error +message B<and> set C<errno>, then return C<-1>. + +=head2 C<.flush> + + int flush (void *handle, + int (*next) (void *data), void *data); + +This intercepts the plugin C<.flush> method and can be used to modify +flush requests. + +If there is an error, C<.flush> should call C<nbdkit_error> with an +error message B<and> set C<errno>, then return C<-1>. + +=head2 C<.trim> + + int trim (void *handle, uint32_t count, uint64_t offset, + int (*next) (void *data, uint32_t count, uint64_t offset), + void *data); + +This intercepts the plugin C<.trim> method and can be used to modify +trim requests. + +If there is an error, C<.trim> should call C<nbdkit_error> with an +error message B<and> set C<errno>, then return C<-1>. + +=head2 C<.zero> + + int zero (void *handle, uint32_t count, uint64_t offset, int may_trim, + int (*next) (void *data, + uint32_t count, uint64_t offset, int may_trim), + void *data); + +This intercepts the plugin C<.zero> method and can be used to modify +zero requests. + +If there is an error, C<.zero> should call C<nbdkit_error> with an +error message B<and> set C<errno>, then return C<-1>. + +=head1 THREADS + +Because filters can be mixed and used with any plugin and thus any +threading model supported by L<nbdkit-plugin(3)>, filters must be +thread safe. They must be able to handle concurrent requests even on +the same handle. + +Filters may have to use pthread primitives like mutexes to achieve +this. + +=head1 DEBUGGING + +Run the server with I<-f> and I<-v> options so it doesn't fork and you +can see debugging information: + + nbdkit -fv --filter=./myfilter.so plugin [key=value [key=value [...]]] + +To print debugging information from within the filter, call +C<nbdkit_debug>, which has the following prototype and works like +L<printf(3)>: + + void nbdkit_debug (const char *fs, ...); + void nbdkit_vdebug (const char *fs, va_list args); + +For convenience, C<nbdkit_debug> preserves the value of C<errno>. +Note that C<nbdkit_debug> only prints things when the server is in +verbose mode (I<-v> option). + +=head1 INSTALLING THE FILTER + +The filter is a C<*.so> file and possibly a manual page. You can of +course install the filter C<*.so> file wherever you want, and users +will be able to use it by running: + + nbdkit --filter=/path/to/filter.so plugin [args] + +However B<if> the shared library has a name of the form +C<nbdkit-I<name>-filter.so> B<and if> the library is installed in the +C<$filterdir> directory, then users can be run it by only typing: + + nbdkit --filter=name plugin [args] + +The location of the C<$filterdir> directory is set when nbdkit is +compiled and can be found by doing: + + nbdkit --dump-config + +If using the pkg-config/pkgconf system then you can also find the +filter directory at compile time by doing: + + pkgconf nbdkit --variable=filterdir + +=head1 PKG-CONFIG/PKGCONF + +nbdkit provides a pkg-config/pkgconf file called C<nbdkit.pc> which +should be installed on the correct path when the nbdkit development +environment is installed. You can use this in autoconf +F<configure.ac> scripts to test for the development environment: + + PKG_CHECK_MODULES([NBDKIT], [nbdkit >= 1.2.3]) + +The above will fail unless nbdkit E<ge> 1.2.3 and the header file is +installed, and will set C<NBDKIT_CFLAGS> and C<NBDKIT_LIBS> +appropriately for compiling filters. + +You can also run pkg-config/pkgconf directly, for example: + + if ! pkgconf nbdkit --exists; then + echo "you must install the nbdkit development environment" + exit 1 + fi + +=head1 SEE ALSO + +L<nbdkit(1)>, +L<nbdkit-plugin(1)>. + +=head1 AUTHORS + +Richard W.M. Jones + +=head1 COPYRIGHT + +Copyright (C) 2013-2018 Red Hat Inc. + +=head1 LICENSE + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions are +met: + +=over 4 + +=item * + +Redistributions of source code must retain the above copyright +notice, this list of conditions and the following disclaimer. + +=item * + +Redistributions in binary form must reproduce the above copyright +notice, this list of conditions and the following disclaimer in the +documentation and/or other materials provided with the distribution. + +=item * + +Neither the name of Red Hat nor the names of its contributors may be +used to endorse or promote products derived from this software without +specific prior written permission. + +=back + +THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +SUCH DAMAGE. diff --git a/docs/nbdkit-plugin.pod b/docs/nbdkit-plugin.pod index 9abf75f..3cafc42 100644 --- a/docs/nbdkit-plugin.pod +++ b/docs/nbdkit-plugin.pod @@ -692,6 +692,7 @@ and then users will be able to run it like this: =head1 SEE ALSO L<nbdkit(1)>, +L<nbdkit-filter(3)>, L<nbdkit-example1-plugin(1)>, L<nbdkit-example2-plugin(1)>, L<nbdkit-example3-plugin(1)>, @@ -711,7 +712,7 @@ Pino Toscano =head1 COPYRIGHT -Copyright (C) 2013-2017 Red Hat Inc. +Copyright (C) 2013-2018 Red Hat Inc. =head1 LICENSE diff --git a/docs/nbdkit.pod b/docs/nbdkit.pod index 1687ac9..3b37db8 100644 --- a/docs/nbdkit.pod +++ b/docs/nbdkit.pod @@ -856,6 +856,7 @@ L</SOCKET ACTIVATION>. Other nbdkit manual pages: L<nbdkit-plugin(3)>, +L<nbdkit-filter(3)>, L<nbdkit-curl-plugin(1)>, L<nbdkit-example1-plugin(1)>, L<nbdkit-example2-plugin(1)>, @@ -895,7 +896,7 @@ Pino Toscano =head1 COPYRIGHT -Copyright (C) 2013-2017 Red Hat Inc. +Copyright (C) 2013-2018 Red Hat Inc. =head1 LICENSE diff --git a/filters/Makefile.am b/filters/Makefile.am new file mode 100644 index 0000000..ed1580b --- /dev/null +++ b/filters/Makefile.am @@ -0,0 +1,33 @@ +# nbdkit +# Copyright (C) 2013-2018 Red Hat Inc. +# All rights reserved. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +#SUBDIRS = diff --git a/include/Makefile.am b/include/Makefile.am index 7d54215..deccc6b 100644 --- a/include/Makefile.am +++ b/include/Makefile.am @@ -30,4 +30,6 @@ # OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF # SUCH DAMAGE. -include_HEADERS = nbdkit-plugin.h +include_HEADERS = \ + nbdkit-plugin.h \ + nbdkit-filter.h diff --git a/include/nbdkit-filter.h b/include/nbdkit-filter.h new file mode 100644 index 0000000..789bbb0 --- /dev/null +++ b/include/nbdkit-filter.h @@ -0,0 +1,132 @@ +/* nbdkit + * Copyright (C) 2013-2017 Red Hat Inc. + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * * Neither the name of Red Hat nor the names of its contributors may be + * used to endorse or promote products derived from this software without + * specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +/* 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 + +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) (const char *key, const char *value, + int (*next) (void *data, const char *key, const char *value), + void *data); + int (*config_complete) (int (*next) (void *data), void *data); + const char *config_help; + + void * (*open) (int readonly, + int (*next) (void *data, int readonly), void *data); + void (*close) (void *handle, + void (*next) (void *data), void *data); + + int64_t (*get_size) (void *handle, + int64_t (*next) (void *data), void *data); + + int (*can_write) (void *handle, + int (*next) (void *data), void *data); + int (*can_flush) (void *handle, + int (*next) (void *data), void *data); + int (*is_rotational) (void *handle, + int (*next) (void *data), void *data); + int (*can_trim) (void *handle, + int (*next) (void *data), void *data); + + int (*pread) (void *handle, void *buf, uint32_t count, uint64_t offset, + int (*next) (void *data, + void *buf, uint32_t count, uint64_t offset), + void *data); + int (*pwrite) (void *handle, const void *buf, uint32_t count, uint64_t offset, + int (*next) (void *data, + const void *buf, uint32_t count, uint64_t offset), + void *data); + int (*flush) (void *handle, + int (*next) (void *data), void *data); + int (*trim) (void *handle, uint32_t count, uint64_t offset, + int (*next) (void *data, uint32_t count, uint64_t offset), + void *data); + int (*zero) (void *handle, uint32_t count, uint64_t offset, int may_trim, + int (*next) (void *data, + uint32_t count, uint64_t offset, int may_trim), + void *data); +}; + +#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 */ diff --git a/include/nbdkit-plugin.h b/include/nbdkit-plugin.h index 2ec3b15..13541e5 100644 --- a/include/nbdkit-plugin.h +++ b/include/nbdkit-plugin.h @@ -111,11 +111,13 @@ extern char *nbdkit_absolute_path (const char *path); extern int64_t nbdkit_parse_size (const char *str); extern int nbdkit_read_password (const char *value, char **password); +#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_PLUGIN(plugin) \ NBDKIT_CXX_LANG_C \ diff --git a/src/Makefile.am b/src/Makefile.am index 12b9043..47d5f38 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -31,6 +31,7 @@ # SUCH DAMAGE. plugindir = $(libdir)/nbdkit/plugins +filterdir = $(libdir)/nbdkit/filters sbin_PROGRAMS = nbdkit @@ -46,13 +47,15 @@ nbdkit_SOURCES = \ sockets.c \ threadlocal.c \ utils.c \ - $(top_srcdir)/include/nbdkit-plugin.h + $(top_srcdir)/include/nbdkit-plugin.h \ + $(top_srcdir)/include/nbdkit-filter.h nbdkit_CPPFLAGS = \ -Dbindir=\"$(bindir)\" \ -Dlibdir=\"$(libdir)\" \ -Dmandir=\"$(mandir)\" \ -Dplugindir=\"$(plugindir)\" \ + -Dfilterdir=\"$(filterdir)\" \ -Dsbindir=\"$(sbindir)\" \ -Dsysconfdir=\"$(sysconfdir)\" \ -I$(top_srcdir)/include diff --git a/src/main.c b/src/main.c index 4eca859..9b66d55 100644 --- a/src/main.c +++ b/src/main.c @@ -176,6 +176,7 @@ dump_config (void) printf ("%s=%s\n", "mandir", mandir); printf ("%s=%s\n", "name", PACKAGE_NAME); printf ("%s=%s\n", "plugindir", plugindir); + printf ("%s=%s\n", "filterdir", filterdir); printf ("%s=%s\n", "root_tls_certificates_dir", root_tls_certificates_dir); printf ("%s=%s\n", "sbindir", sbindir); #ifdef HAVE_LIBSELINUX diff --git a/src/nbdkit.pc.in b/src/nbdkit.pc.in index cbb301d..fe8f511 100644 --- a/src/nbdkit.pc.in +++ b/src/nbdkit.pc.in @@ -3,6 +3,7 @@ exec_prefix=@exec_prefix@ libdir=@libdir@ includedir=@includedir@ plugindir=@libdir@/nbdkit/plugins +filterdir=@libdir@/nbdkit/filters Name: @PACKAGE_NAME@ Version: @PACKAGE_VERSION@ -- 2.15.1