=head1 NAME

nbdkit-memory-plugin - nbdkit virtual memory (RAM disk) plugin

=head1 SYNOPSIS

 nbdkit memory [size=]SIZE

=head1 DESCRIPTION

C<nbdkit-memory-plugin> is a plugin for L<nbdkit(1)> which stores a
single disk image in virtual memory, and discards it when nbdkit
exits.  This plugin can be used for testing or where you don't care
about the final content of the disk image.

All nbdkit clients will see the same disk content, initially all
zeroes.

The disk image is stored in memory using a sparse array.  The
allocated parts of the disk image cannot be larger than physical RAM
plus swap, less whatever is being used by the rest of the system.  If
you want to allocate more space than this use L<nbdkit-file-plugin(1)>
backed by a temporary file instead.

However the virtual size can be as large as you like, up to the
maximum supported by nbdkit (S<2⁶³-1 bytes>).  This limit is tested
when nbdkit is compiled, and it should work on all platforms and
architectures supported by nbdkit.

=head1 EXAMPLES

Create a one gigabyte sparse RAM disk:

 nbdkit memory 1G

If you want to loop mount the above disk, see L<nbdkit-loop(1)>.

Create the largest possible RAM disk:

 nbdkit memory $(( 2**63 - 1 ))

=head1 PARAMETERS

=over 4

=item [B<size=>]SIZE

Specify the virtual size of the disk image.

This parameter is required.

C<size=> is a magic config key and may be omitted in most cases.
See L<nbdkit(1)/Magic parameters>.

=back

=head1 NOTES

=head2 Preloading small amounts of data

If you want an in-memory disk image preinitialized with a small amount
of data specified on the command line, look at
L<nbdkit-data-plugin(1)> instead.  Note by "small" this does not mean
that the virtual disk image must be small, but that the amount of data
initially stored sparsely is small enough to specify on the command
line.

=head2 Preloading large amounts of data

If you want to preload a large amount of data (eg. a disk image) into
the memory plugin, use L<qemu-img(1)>:

 $ rm -f pid
 $ nbdkit -P pid memory 10G
 
 # wait for nbdkit to become ready to accept connections:
 $ while [ ! -f pid ]; do sleep 1; done
 
 # preload Fedora disk image:
 $ virt-builder fedora-28 --size=10G
 $ qemu-img convert -p -n fedora-28.img nbd:localhost:10809

=head1 FILES

=over 4

=item F<$plugindir/nbdkit-memory-plugin.so>

The plugin.

Use C<nbdkit --dump-config> to find the location of C<$plugindir>.

=back

=head1 VERSION

C<nbdkit-memory-plugin> first appeared in nbdkit 1.2.

=head1 SEE ALSO

L<nbdkit(1)>,
L<nbdkit-plugin(3)>,
L<nbdkit-loop(1)>,
L<nbdkit-data-plugin(1)>,
L<nbdkit-file-plugin(1)>,
L<nbdkit-info-plugin(1)>.

=head1 AUTHORS

Richard W.M. Jones

=head1 COPYRIGHT

Copyright (C) 2017-2018 Red Hat Inc.
