Provided by: nbdkit_1.42.2-1ubuntu1_amd64 
NAME
nbdkit-cc-plugin - write small nbdkit plugins in inline C (and other languages)
SYNOPSIS
nbdkit cc /path/to/plugin.c [CC=<CC>] [CFLAGS=<CFLAGS>]
[EXTRA_CFLAGS=<EXTRA_CFLAGS>]
nbdkit cc - <<'EOF'
... C code ...
EOF
DESCRIPTION
This plugin allows you to write small nbdkit(1) plugins in C (and some other languages). When you use
this plugin it compiles your source code to a temporary plugin and then jumps into your compiled plugin.
It is somewhat similar to nbdkit-sh-plugin(3), except for C source code. This can also be used to write
plugins which are "C scripts".
Note this is not the way you normally write nbdkit plugins in C. To understand how to write plugins in C
normally, read nbdkit-plugin(3).
Simple plugin example
Simple plugins from the nbdkit source tree can be compiled and run directly using commands such as:
$ nbdkit cc plugins/example1/example1.c EXTRA_CFLAGS="-I. -Iinclude"
You can also read the source from stdin using "-":
$ nbdkit cc - EXTRA_CFLAGS="-I. -Iinclude" \
< plugins/example1/example1.c
To replace the compiler flags:
$ nbdkit cc plugins/example1/example1.c \
CFLAGS="-O3 -mavx2 -fPIC -shared"
Compiler name and flags
The plugin parameters "CC", "CFLAGS" and "EXTRA_CFLAGS" (written in uppercase) can be used to control
which C compiler and C compiler flags are used. If not set, the default compiler and flags from when
nbdkit was itself compiled from source are used. To see what those were you can do:
$ nbdkit cc --dump-plugin
...
CC=gcc
CFLAGS=-g -O2 -fPIC -shared
The "CFLAGS" parameter overrides the built-in flags completely. The "EXTRA_CFLAGS" parameter adds extra
flags to the built-in flags.
Plugin API version
Plugins compiled this way must use the same API version as the cc plugin itself uses. Currently this is
"NBDKIT_API_VERSION=2".
C plugin as a self-contained script
You can create a C plugin which is a self-contained script by adding the following lines at the top and
ensuring the C source is executable ("chmod +x plugin.c"):
#if 0
exec nbdkit cc "$0" "$@"
#endif
The script can be run as a command with additional nbdkit flags and plugin parameters, eg:
./plugin.c -f -v
./plugin.c -p 10000 --filter=cow
./plugin.c param=1
Using this plugin with C++
nbdkit cc CC=g++ source.cpp
C++ plugin scripts can be created similarly to C, but you must add "CC=g++" as a parameter to exec
nbdkit.
Using this plugin with OCaml
nbdkit cc CC=ocamlopt \
CFLAGS="-output-obj -runtime-variant _pic NBDKit.cmx -cclib -lnbdkitocaml" \
source.ml
OCaml plugin scripts can be created using this trick:
(*/.)>/dev/null 2>&1
exec nbdkit cc "$0" \
CC=ocamlopt \
CFLAGS="-output-obj -runtime-variant _pic NBDKit.cmx -cclib -lnbdkitocaml" \
"$@"
*)
(* followed by OCaml code for the plugin here *)
As with C plugin scripts, the file must be executable. See also nbdkit-ocaml-plugin(3).
Using this plugin with other programming languages
This plugin can be used with most ahead-of-time compiled programming languages if they can create shared
objects (.so files). The only requirement is that the compiler ("CC") supports an -o option to write a
shared object.
PARAMETERS
The script name, or "-", must appear as the first parameter.
CC=CC
CFLAGS="CFLAGS"
EXTRA_CFLAGS="EXTRA_CFLAGS"
Override the compiler and flags. See "Compiler name and flags" above.
All other parameters on the command line are passed to the plugin.
EXAMPLE
$ nbdkit cc - <<'EOF'
#include <stdint.h>
#include <string.h>
#define NBDKIT_API_VERSION 2
#include <nbdkit-plugin.h>
char data[10*1024*1024];
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
static void *
my_open (int readonly)
{
return NBDKIT_HANDLE_NOT_NEEDED;
}
static int64_t
my_get_size (void *handle)
{
return (int64_t) sizeof (data);
}
static int
my_pread (void *handle, void *buf,
uint32_t count, uint64_t offset,
uint32_t flags)
{
memcpy (buf, data+offset, count);
return 0;
}
static int
my_pwrite (void *handle, const void *buf,
uint32_t count, uint64_t offset,
uint32_t flags)
{
memcpy (data+offset, buf, count);
return 0;
}
static struct nbdkit_plugin plugin = {
.name = "myplugin",
.open = my_open,
.get_size = my_get_size,
.pread = my_pread,
.pwrite = my_pwrite,
};
NBDKIT_REGISTER_PLUGIN(plugin)
EOF
FILES
$plugindir/nbdkit-cc-plugin.so
The plugin.
Use "nbdkit --dump-config" to find the location of $plugindir.
VERSION
"nbdkit-cc-plugin" first appeared in nbdkit 1.22.
SEE ALSO
nbdkit(1), nbdkit-plugin(3), nbdkit-eval-plugin(3), nbdkit-ocaml-plugin(3), nbdkit-sh-plugin(3).
AUTHORS
Richard W.M. Jones
COPYRIGHT
Copyright Red Hat
LICENSE
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.
nbdkit-1.42.2 2025-04-02 nbdkit-cc-plugin(3)