guestfs-ocaml - How to use libguestfs from OCaml
let g = Guestfs.create () in Guestfs.add_drive_opts g ~format:"raw" ~readonly:true "disk.img"; Guestfs.launch g;
let g = new Guestfs.guestfs () in g#add_drive_opts ~format:"raw" ~readonly:true "disk.img"; g#launch (); ocamlfind opt prog.ml -package guestfs -linkpkg -o prog or: ocamlopt -I +guestfs mlguestfs.cmxa prog.ml -o prog
This manual page documents how to call libguestfs from the OCaml programming language. This page just documents the differences from the C API and gives some examples. If you are not familiar with using libguestfs, you also need to read guestfs(3).
There are two different programming styles supported by the OCaml bindings. You can use a module style, with each C function mapped to an OCaml function:
int guestfs_set_verbose (guestfs_h *g, int flag);
val Guestfs.set_verbose : Guestfs.t -> bool -> unit
Alternately you can use an object-oriented style, calling methods on the class
method set_verbose : bool -> unit
The object-oriented style is usually briefer, and the minor performance penalty isn't noticeable in the general overhead of performing libguestfs functions.
The handle is closed when it is reaped by the garbage collector. Because libguestfs handles include a lot of state, it is also possible to close (and hence free) them explicitly by calling
Guestfs.close or the
Errors from libguestfs functions are mapped into the
Guestfs.Error exception. This has a single parameter which is the error message (a string).
Calling any function/method on a closed handle raises
Guestfs.Handle_closed. The single parameter is the name of the function that you called.
(* Example showing how to create a disk image. *) open Unix open Printf let output = "disk.img" let () = let g = new Guestfs.guestfs () in (* Create a raw-format sparse disk image, 512 MB in size. *) let fd = openfile output [O_WRONLY;O_CREAT;O_TRUNC;O_NOCTTY] 0o666 in ftruncate fd (512 * 1024 * 1024); close fd; (* Set the trace flag so that we can see each libguestfs call. *) g#set_trace true; (* Attach the disk image to libguestfs. *) g#add_drive_opts ~format:"raw" ~readonly:false output; (* Run the libguestfs back-end. *) g#launch (); (* Get the list of devices. Because we only added one drive * above, we expect that this list should contain a single * element. *) let devices = g#list_devices () in if Array.length devices <> 1 then failwith "error: expected a single device from list-devices"; (* Partition the disk as one single MBR partition. *) g#part_disk devices.(0) "mbr"; (* Get the list of partitions. We expect a single element, which * is the partition we have just created. *) let partitions = g#list_partitions () in if Array.length partitions <> 1 then failwith "error: expected a single partition from list-partitions"; (* Create a filesystem on the partition. *) g#mkfs "ext4" partitions.(0); (* Now mount the filesystem so that we can add files. *) g#mount partitions.(0) "/"; (* Create some files and directories. *) g#touch "/empty"; let message = "Hello, world\n" in g#write "/hello" message; g#mkdir "/foo"; (* This one uploads the local file /etc/resolv.conf into * the disk image. *) g#upload "/etc/resolv.conf" "/foo/resolv.conf"; (* Because we wrote to the disk and we want to detect write * errors, call g#shutdown. You don't need to do this: * g#close will do it implicitly. *) g#shutdown (); (* Note also that handles are automatically closed if they are * reaped by the garbage collector. You only need to call close * if you want to close the handle right away. *) g#close ()
(* Example showing how to inspect a virtual machine disk. *) open Printf let disk = if Array.length Sys.argv = 2 then Sys.argv.(1) else failwith "usage: inspect_vm disk.img" let () = let g = new Guestfs.guestfs () in (* Attach the disk image read-only to libguestfs. *) g#add_drive_opts (*~format:"raw"*) ~readonly:true disk; (* Run the libguestfs back-end. *) g#launch (); (* Ask libguestfs to inspect for operating systems. *) let roots = g#inspect_os () in if Array.length roots = 0 then failwith "inspect_vm: no operating systems found"; Array.iter ( fun root -> printf "Root device: %s\n" root; (* Print basic information about the operating system. *) printf " Product name: %s\n" (g#inspect_get_product_name root); printf " Version: %d.%d\n" (g#inspect_get_major_version root) (g#inspect_get_minor_version root); printf " Type: %s\n" (g#inspect_get_type root); printf " Distro: %s\n" (g#inspect_get_distro root); (* Mount up the disks, like guestfish -i. * * Sort keys by length, shortest first, so that we end up * mounting the filesystems in the correct order. *) let mps = g#inspect_get_mountpoints root in let cmp (a,_) (b,_) = compare (String.length a) (String.length b) in let mps = List.sort cmp mps in List.iter ( fun (mp, dev) -> try g#mount_ro dev mp with Guestfs.Error msg -> eprintf "%s (ignored)\n" msg ) mps; (* If /etc/issue.net file exists, print up to 3 lines. *) let filename = "/etc/issue.net" in if g#is_file filename then ( printf "--- %s ---\n" filename; let lines = g#head_n 3 filename in Array.iter print_endline lines ); (* Unmount everything. *) g#umount_all () ) roots
guestfs(3), guestfs-examples(3), guestfs-erlang(3), guestfs-java(3), guestfs-lua(3), guestfs-perl(3), guestfs-python(3), guestfs-recipes(1), guestfs-ruby(3), http://libguestfs.org/, http://caml.inria.fr/.
Richard W.M. Jones (
rjones at redhat dot com)
Copyright (C) 2010-2012 Red Hat Inc.
This manual page contains examples which we hope you will use in your programs. The examples may be freely copied, modified and distributed for any purpose without any restrictions.
To get a list of bugs against libguestfs, use this link: https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools
To report a new bug against libguestfs, use this link: https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools
When reporting a bug, please supply:
The version of libguestfs.
Where you got libguestfs (eg. which Linux distro, compiled from source, etc)
Describe the bug accurately and give a way to reproduce it.
Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug report.