libguestfs/README

libguestfs is a library for accessing and modifying guest disk images.
Amongst the things this is good for: making batch configuration
changes to guests, getting disk used/free statistics (see also:
virt-df), migrating between virtualization systems (see also:
virt-p2v), performing partial backups, performing partial guest
clones, cloning guests and changing registry/UUID/hostname info, and
much else besides.

libguestfs uses Linux kernel and qemu code, and can access any type of
guest filesystem that Linux and qemu can, including but not limited
to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
schemes, qcow, qcow2, vmdk.

libguestfs provides ways to enumerate guest storage (eg. partitions,
LVs, what filesystem is in each LV, etc.).  It can also run commands
in the context of the guest.  Also you can mount guest filesystems on
the host (requires root privs and NFS).

libguestfs is a library that can be linked with C and C++ management
programs (or management programs written in other languages, if people
contribute the language bindings).  You can also use it from shell
scripts or the command line.

libguestfs was written by Richard W.M. Jones (rjones@redhat.com).
For discussion please use the fedora-virt mailing list:

  https://www.redhat.com/mailman/listinfo/fedora-virt


Requirements
----------------------------------------------------------------------

- nfs-utils source, unpacked
  http://download.sourceforge.net/nfs

- Recent QEMU with vmchannel support

- Compiled Linux kernels for 32 and/or 64 bit (see note below).

- mkinitrd

- cpio

- XDR, rpcgen

- If you are running a 64 bit or non-x86 machine, see note below.

We don't support initramfs at the moment.  Patches gratefully
received.

Running ./configure will check you have all the requirements installed
on your machine.


Building
----------------------------------------------------------------------

Unpack nfs-utils source into a directory somewhere, then create a
symlink daemon/nfs-utils to where you unpacked it.  For example:

  pushd daemon
  tar zxf /path/to/nfs-utils-1.1.4.tar.gz
  ln -s nfs-utils-1.1.4 nfs-utils
  popd

For nfs-utils 1.1.4, you may find that the patch
(nfs-utils-1.1.4-build.patch) helps.

Then make the library and shell tools:

  ./configure
  make

Make the daemon and NFS server:
  mkdir daemon/build
  pushd daemon/build
  ../configure
  make
  popd

For 64 bit you'll probably want to build the 32 bit daemon and NFS
server too:

  mkdir daemon/build-32
  pushd daemon/build-32
  ../configure --enable-32bit
  make
  popd

For complex cross-architecture environments, you may want to build
other versions of the daemon and NFS server as well.  See the note
below.

Finally run the tests:

  make check

If everything works, you can install the library and tools by running
these commands as root:

  make install

  pushd daemon/build
  make install
  popd
  # Repeat for each daemon/build* directory you made above.


Note on 64 bit and non-x86 architectures
----------------------------------------------------------------------

The library runs the Linux kernel code in QEMU.  It also runs a small
control daemon inside QEMU.  It might also run an NFS server.  It
might also run programs from the guest's disk/environment (if asked to).

This leaves open the question of which QEMU do we run, eg. qemu (the
i386 emulator) or qemu-system-x86_64 or qemu-system-ppc64 or ...?

Several factors influence the choice:

(a) The host architecture.

(b) The guest architecture.

(c) What kernel(s) we find at runtime.

(d) What compiler(s) we find at configure time.

(e) In general, we would prefer to run a 32 bit kernel over a 64 bit
kernel, because that reduces the amount of system memory we have to
give to qemu significantly, and makes libguestfs smaller, faster and
use less memory.

For example, if (a) the host is x86-64, then it might be running a
mixture of (b) i386 and x86-64 guests.  Disk formats are stable, even
across 32 and 64 bit and endianness changes, so it doesn't really
matter what kernel we use if we just want to access files in the
guest.  In the absence of any other factors, we would choose an i386
kernel and run it in plain 'qemu', because that would use the least
amount of memory.

But if we wanted to enable the feature of running a guest program in
an x86-64 guest, then we have to run an x86-64 kernel and
qemu-system-x86_64 (an i386 kernel can't run 64 bit programs).  The
same applies if we didn't find a 32 bit kernel at runtime, or if we
couldn't run "gcc -m32" at configure time (because we can't compile
the daemon).

SO: to enable maximum features on 64 bit architectures:

(1) Ensure that "gcc -m32" can create usable binaries.

(2) Provide 32 and 64 bit kernels binaries at runtime.

If you have a really weird environment, eg. you want to run programs
inside PPC64 guests on your MIPS machine, then:

(3) Provide gcc cross-compiler and glibc for each architecture, and
cross-compile the daemon and NFS server:

  mkdir daemon/build-ppc64
  pushd daemon/build-ppc64
  ../configure --host=ppc64-gnu-linux
  make
  popd


Copyright and license information
----------------------------------------------------------------------

Copyright (C) 2009 Red Hat Inc.

The library is distributed under the LGPLv2+.  The programs are
distributed under the GPLv2+.  Please see the files COPYING and
COPYING.LIB for full license information.