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.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
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.\" ========================================================================
.\"
.IX Title "nbdkit-ruby-plugin 3"
.TH nbdkit-ruby-plugin 3 "2016-06-21" "nbdkit" "nbdkit"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
nbdkit\-ruby\-plugin \- nbdkit ruby plugin
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit ruby script=/path/to/plugin.rb [arguments...]
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-ruby\-plugin\*(C'\fR is an embedded Ruby interpreter for
\&\fInbdkit\fR\|(1), allowing you to write nbdkit plugins in Ruby.
.PP
Broadly speaking, Ruby nbdkit plugins work like C ones, so you should
read \fInbdkit\-plugin\fR\|(3) first.
.SS "\s-1USING A RUBY NBDKIT PLUGIN\s0"
.IX Subsection "USING A RUBY NBDKIT PLUGIN"
Assuming you have a Ruby script which is an nbdkit plugin, you run it
like this:
.PP
.Vb 1
\& nbdkit ruby script=/path/to/ruby.rb
.Ve
.PP
You may have to add further \f(CW\*(C`key=value\*(C'\fR arguments to the command
line.  Read the Ruby script to see if it requires any.  \f(CW\*(C`script=...\*(C'\fR
\&\fImust\fR come first on the command line.
.SH "WRITING A RUBY NBDKIT PLUGIN"
.IX Header "WRITING A RUBY NBDKIT PLUGIN"
There is an example Ruby nbdkit plugin called \f(CW\*(C`example.rb\*(C'\fR which
ships with the nbdkit source.
.PP
To write a Ruby nbdkit plugin, you create a Ruby file which
contains at least the following required functions:
.PP
.Vb 9
\& def open(readonly)
\&   # see below
\& end
\& def get_size(h)
\&   # see below
\& end
\& def pread(h, count, offset)
\&   # see below
\& end
.Ve
.PP
Note that the subroutines must have those literal names (like \f(CW\*(C`open\*(C'\fR),
because the C part looks up and calls those functions directly.  You
may want to include documentation and globals (eg. for storing global
state).  Any other top level statements are run when the script is
loaded, just like ordinary Ruby.
.PP
The file does not need to include a \f(CW\*(C`#!\*(C'\fR (hash-bang) at the top, and
does not need to be executable.  In fact it's a good idea not to do
that, because running the plugin directly as a Ruby script won't
work.
.SS "\s-1EXCEPTIONS\s0"
.IX Subsection "EXCEPTIONS"
Ruby callbacks should throw exceptions to indicate errors.
.SS "\s-1RUBY CALLBACKS\s0"
.IX Subsection "RUBY CALLBACKS"
This just documents the arguments to the callbacks in Ruby, and any
way that they differ from the C callbacks.  In all other respects they
work the same way as the C callbacks, so you should go and read
\&\fInbdkit\-plugin\fR\|(3).
.ie n .IP """config""" 4
.el .IP "\f(CWconfig\fR" 4
.IX Item "config"
(Optional)
.Sp
.Vb 3
\& def config(key, value)
\&   # no return value
\& end
.Ve
.ie n .IP """config_complete""" 4
.el .IP "\f(CWconfig_complete\fR" 4
.IX Item "config_complete"
(Optional)
.Sp
There are no arguments or return value.
.ie n .IP """open""" 4
.el .IP "\f(CWopen\fR" 4
.IX Item "open"
(Required)
.Sp
.Vb 3
\& def open(readonly)
\&   # return handle
\& end
.Ve
.Sp
You can return any non-nil Ruby value as the handle.  It is passed
back in subsequent calls.
.ie n .IP """close""" 4
.el .IP "\f(CWclose\fR" 4
.IX Item "close"
(Optional)
.Sp
.Vb 3
\& def close(h)
\&   # no return value
\& end
.Ve
.ie n .IP """get_size""" 4
.el .IP "\f(CWget_size\fR" 4
.IX Item "get_size"
(Required)
.Sp
.Vb 3
\& def get_size(h)
\&   # return the size of the disk
\& end
.Ve
.ie n .IP """can_write""" 4
.el .IP "\f(CWcan_write\fR" 4
.IX Item "can_write"
(Optional)
.Sp
.Vb 3
\& def can_write(h)
\&   # return a boolean
\& end
.Ve
.ie n .IP """can_flush""" 4
.el .IP "\f(CWcan_flush\fR" 4
.IX Item "can_flush"
(Optional)
.Sp
.Vb 3
\& def can_flush(h)
\&   # return a boolean
\& end
.Ve
.ie n .IP """is_rotational""" 4
.el .IP "\f(CWis_rotational\fR" 4
.IX Item "is_rotational"
(Optional)
.Sp
.Vb 3
\& def is_rotational(h)
\&   # return a boolean
\& end
.Ve
.ie n .IP """can_trim""" 4
.el .IP "\f(CWcan_trim\fR" 4
.IX Item "can_trim"
(Optional)
.Sp
.Vb 3
\& def can_trim(h)
\&   # return a boolean
\& end
.Ve
.ie n .IP """pread""" 4
.el .IP "\f(CWpread\fR" 4
.IX Item "pread"
(Required)
.Sp
.Vb 3
\& def pread(h, count, offset)
\&   # construct a string of length count bytes and return it
\& end
.Ve
.Sp
The body of your \f(CW\*(C`pread\*(C'\fR function should construct a string of length
(at least) \f(CW\*(C`count\*(C'\fR bytes.  You should read \f(CW\*(C`count\*(C'\fR bytes from the
disk starting at \f(CW\*(C`offset\*(C'\fR.
.Sp
\&\s-1NBD\s0 only supports whole reads, so your function should try to read
the whole region (perhaps requiring a loop).  If the read fails or
is partial, your function should throw an exception.
.ie n .IP """pwrite""" 4
.el .IP "\f(CWpwrite\fR" 4
.IX Item "pwrite"
(Optional)
.Sp
.Vb 4
\& def pwrite(h, buf, offset)
\&   length = buf.length
\&   # no return value
\& end
.Ve
.Sp
The body of your \f(CW\*(C`pwrite\*(C'\fR function should write the \f(CW\*(C`buf\*(C'\fR string to
the disk.  You should write \f(CW\*(C`count\*(C'\fR bytes to the disk starting at
\&\f(CW\*(C`offset\*(C'\fR.
.Sp
\&\s-1NBD\s0 only supports whole writes, so your function should try to
write the whole region (perhaps requiring a loop).  If the write
fails or is partial, your function should throw an exception.
.ie n .IP """flush""" 4
.el .IP "\f(CWflush\fR" 4
.IX Item "flush"
(Optional)
.Sp
.Vb 3
\& def flush(h)
\&   # no return value
\& end
.Ve
.Sp
The body of your \f(CW\*(C`flush\*(C'\fR function should do a \fIsync\fR\|(2) or
\&\fIfdatasync\fR\|(2) or equivalent on the backing store.
.ie n .IP """trim""" 4
.el .IP "\f(CWtrim\fR" 4
.IX Item "trim"
(Optional)
.Sp
.Vb 3
\& def trim(h, count, offset)
\&   # no return value
\& end
.Ve
.Sp
The body of your \f(CW\*(C`trim\*(C'\fR function should \*(L"punch a hole\*(R" in the
backing store.
.SS "\s-1MISSING CALLBACKS\s0"
.IX Subsection "MISSING CALLBACKS"
.ie n .IP "Missing: ""load"" and ""unload""" 4
.el .IP "Missing: \f(CWload\fR and \f(CWunload\fR" 4
.IX Item "Missing: load and unload"
These are not needed because you can just use ordinary Ruby
constructs.
.ie n .IP "Missing: ""name"", ""version"", ""longname"", ""description"", ""config_help""" 4
.el .IP "Missing: \f(CWname\fR, \f(CWversion\fR, \f(CWlongname\fR, \f(CWdescription\fR, \f(CWconfig_help\fR" 4
.IX Item "Missing: name, version, longname, description, config_help"
These are not yet supported.
.SS "\s-1THREADS\s0"
.IX Subsection "THREADS"
The thread model for Ruby callbacks currently cannot be set from Ruby.
It is hard-coded in the C part to
\&\f(CW\*(C`NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS\*(C'\fR.  This may change or be
settable in future.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fInbdkit\fR\|(1),
\&\fInbdkit\-plugin\fR\|(3),
\&\fIruby\fR\|(1).
.SH "AUTHORS"
.IX Header "AUTHORS"
Richard W.M. Jones
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2013\-2016 Red Hat Inc.
.SH "LICENSE"
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP "\(bu" 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP "\(bu" 4
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.
.IP "\(bu" 4
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.
.PP
\&\s-1THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS \s0''\s-1AS IS\s0'' \s-1AND
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 \s0(\s-1INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES\s0; \s-1LOSS OF
USE, DATA, OR PROFITS\s0; \s-1OR BUSINESS INTERRUPTION\s0) \s-1HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT \s0(\s-1INCLUDING NEGLIGENCE OR OTHERWISE\s0) \s-1ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.\s0