1guestfs-ocaml(3)            Virtualization Support            guestfs-ocaml(3)
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3
4

NAME

6       guestfs-ocaml - How to use libguestfs from OCaml
7

SYNOPSIS

9       Module style:
10
11        let g = Guestfs.create () in
12        Guestfs.add_drive_opts g ~format:"raw" ~readonly:true "disk.img";
13        Guestfs.launch g;
14
15       Object-oriented style:
16
17        let g = new Guestfs.guestfs () in
18        g#add_drive_opts ~format:"raw" ~readonly:true "disk.img";
19        g#launch ();
20
21        ocamlfind opt prog.ml -package guestfs -linkpkg -o prog
22       or:
23        ocamlopt -I +guestfs mlguestfs.cmxa prog.ml -o prog
24

DESCRIPTION

26       This manual page documents how to call libguestfs from the OCaml
27       programming language.  This page just documents the differences from
28       the C API and gives some examples.  If you are not familiar with using
29       libguestfs, you also need to read guestfs(3).
30
31   PROGRAMMING STYLES
32       There are two different programming styles supported by the OCaml
33       bindings.  You can use a module style, with each C function mapped to
34       an OCaml function:
35
36        int guestfs_set_verbose (guestfs_h *g, int flag);
37
38       becomes:
39
40        val Guestfs.set_verbose : Guestfs.t -> bool -> unit
41
42       Alternately you can use an object-oriented style, calling methods on
43       the class "Guestfs.guestfs":
44
45        method set_verbose : bool -> unit
46
47       The object-oriented style is usually briefer, and the minor performance
48       penalty isn't noticeable in the general overhead of performing
49       libguestfs functions.
50
51   CLOSING THE HANDLE
52       The handle is closed when it is reaped by the garbage collector.
53       Because libguestfs handles include a lot of state, it is also possible
54       to close (and hence free) them explicitly by calling "Guestfs.close" or
55       the "#close" method.
56
57   EXCEPTIONS
58       Errors from libguestfs functions are mapped into the "Guestfs.Error"
59       exception.  This has a single parameter which is the error message (a
60       string).
61
62       Calling any function/method on a closed handle raises
63       "Guestfs.Handle_closed".  The single parameter is the name of the
64       function that you called.
65

EXAMPLE: CREATE A DISK IMAGE

67        (* Example showing how to create a disk image. *)
68
69        open Unix
70        open Printf
71
72        let output = "disk.img"
73
74        let () =
75          let g = new Guestfs.guestfs () in
76
77          (* Create a raw-format sparse disk image, 512 MB in size. *)
78          g#disk_create output "raw" (Int64.of_int (512 * 1024 * 1024));
79
80          (* Set the trace flag so that we can see each libguestfs call. *)
81          g#set_trace true;
82
83          (* Attach the disk image to libguestfs. *)
84          g#add_drive_opts ~format:"raw" ~readonly:false output;
85
86          (* Run the libguestfs back-end. *)
87          g#launch ();
88
89          (* Get the list of devices.  Because we only added one drive
90           * above, we expect that this list should contain a single
91           * element.
92           *)
93          let devices = g#list_devices () in
94          if Array.length devices <> 1 then
95            failwith "error: expected a single device from list-devices";
96
97          (* Partition the disk as one single MBR partition. *)
98          g#part_disk devices.(0) "mbr";
99
100          (* Get the list of partitions.  We expect a single element, which
101           * is the partition we have just created.
102           *)
103          let partitions = g#list_partitions () in
104          if Array.length partitions <> 1 then
105            failwith "error: expected a single partition from list-partitions";
106
107          (* Create a filesystem on the partition. *)
108          g#mkfs "ext4" partitions.(0);
109
110          (* Now mount the filesystem so that we can add files. *)
111          g#mount partitions.(0) "/";
112
113          (* Create some files and directories. *)
114          g#touch "/empty";
115          let message = "Hello, world\n" in
116          g#write "/hello" message;
117          g#mkdir "/foo";
118
119          (* This one uploads the local file /etc/resolv.conf into
120           * the disk image.
121           *)
122          g#upload "/etc/resolv.conf" "/foo/resolv.conf";
123
124          (* Because we wrote to the disk and we want to detect write
125           * errors, call g#shutdown.  You don't need to do this:
126           * g#close will do it implicitly.
127           *)
128          g#shutdown ();
129
130          (* Note also that handles are automatically closed if they are
131           * reaped by the garbage collector.  You only need to call close
132           * if you want to close the handle right away.
133           *)
134          g#close ()
135

EXAMPLE: INSPECT A VIRTUAL MACHINE DISK IMAGE

137        (* Example showing how to inspect a virtual machine disk. *)
138
139        open Printf
140
141        let disk =
142          if Array.length Sys.argv = 2 then
143            Sys.argv.(1)
144          else
145            failwith "usage: inspect_vm disk.img"
146
147        let () =
148          let g = new Guestfs.guestfs () in
149
150          (* Attach the disk image read-only to libguestfs. *)
151          g#add_drive_opts (*~format:"raw"*) ~readonly:true disk;
152
153          (* Run the libguestfs back-end. *)
154          g#launch ();
155
156          (* Ask libguestfs to inspect for operating systems. *)
157          let roots = g#inspect_os () in
158          if Array.length roots = 0 then
159            failwith "inspect_vm: no operating systems found";
160
161          Array.iter (
162            fun root ->
163              printf "Root device: %s\n" root;
164
165              (* Print basic information about the operating system. *)
166              printf "  Product name: %s\n" (g#inspect_get_product_name root);
167              printf "  Version:      %d.%d\n"
168                (g#inspect_get_major_version root)
169                (g#inspect_get_minor_version root);
170              printf "  Type:         %s\n" (g#inspect_get_type root);
171              printf "  Distro:       %s\n" (g#inspect_get_distro root);
172
173              (* Mount up the disks, like guestfish -i.
174               *
175               * Sort keys by length, shortest first, so that we end up
176               * mounting the filesystems in the correct order.
177               *)
178              let mps = g#inspect_get_mountpoints root in
179              let cmp (a,_) (b,_) =
180                compare (String.length a) (String.length b) in
181              let mps = List.sort cmp mps in
182              List.iter (
183                fun (mp, dev) ->
184                  try g#mount_ro dev mp
185                  with Guestfs.Error msg -> eprintf "%s (ignored)\n" msg
186              ) mps;
187
188              (* If /etc/issue.net file exists, print up to 3 lines. *)
189              let filename = "/etc/issue.net" in
190              if g#is_file filename then (
191                printf "--- %s ---\n" filename;
192                let lines = g#head_n 3 filename in
193                Array.iter print_endline lines
194              );
195
196              (* Unmount everything. *)
197              g#umount_all ()
198          ) roots
199

EXAMPLE: ENABLE DEBUGGING AND LOGGING

201        (* Example showing how to enable debugging, and capture it into any
202         * custom logging system.
203         *)
204
205        (* Events we are interested in.  This bitmask covers all trace and
206         * debug messages.
207         *)
208        let event_bitmask = [
209          Guestfs.EVENT_LIBRARY;
210          Guestfs.EVENT_WARNING;
211          Guestfs.EVENT_APPLIANCE;
212          Guestfs.EVENT_TRACE
213        ]
214
215        let rec main () =
216          let g = new Guestfs.guestfs () in
217
218          (* By default, debugging information is printed on stderr.  To
219           * capture it somewhere else you have to set up an event handler
220           * which will be called back as debug messages are generated.  To do
221           * this use the event API.
222           *
223           * For more information see EVENTS in guestfs(3).
224           *)
225          ignore (g#set_event_callback message_callback event_bitmask);
226
227          (* This is how debugging is enabled:
228           *
229           * Setting the 'trace' flag in the handle means that each libguestfs
230           * call is logged (name, parameters, return).  This flag is useful
231           * to see how libguestfs is being used by a program.
232           *
233           * Setting the 'verbose' flag enables a great deal of extra
234           * debugging throughout the system.  This is useful if there is a
235           * libguestfs error which you don't understand.
236           *
237           * Note that you should set the flags early on after creating the
238           * handle.  In particular if you set the verbose flag after launch
239           * then you won't see all messages.
240           *
241           * For more information see:
242           * http://libguestfs.org/guestfs-faq.1.html#debugging-libguestfs
243           *
244           * Error messages raised by APIs are *not* debugging information,
245           * and they are not affected by any of this.  You may have to log
246           * them separately.
247           *)
248          g#set_trace true;
249          g#set_verbose true;
250
251          (* Do some operations which will generate plenty of trace and debug
252           * messages.
253           *)
254          g#add_drive "/dev/null";
255          g#launch ();
256          g#close ()
257
258        (* This function is called back by libguestfs whenever a trace or
259         * debug message is generated.
260         *
261         * For the classes of events we have registered above, 'array' and
262         * 'array_len' will not be meaningful.  Only 'buf' and 'buf_len' will
263         * be interesting and these will contain the trace or debug message.
264         *
265         * This example simply redirects these messages to syslog, but
266         * obviously you could do something more advanced here.
267         *)
268        and message_callback event event_handle buf array =
269          if String.length buf > 0 then (
270            let event_name = Guestfs.event_to_string [event] in
271            Printf.printf "[%s] %S\n%!" event_name buf
272          )
273
274        let () = main ()
275

SEE ALSO

277       guestfs(3), guestfs-examples(3), guestfs-erlang(3), guestfs-gobject(3),
278       guestfs-golang(3), guestfs-java(3), guestfs-lua(3), guestfs-perl(3),
279       guestfs-python(3), guestfs-recipes(1), guestfs-ruby(3),
280       http://libguestfs.org/, http://caml.inria.fr/.
281

AUTHORS

283       Richard W.M. Jones ("rjones at redhat dot com")
284
286       Copyright (C) 2010-2023 Red Hat Inc.
287

LICENSE

289       This manual page contains examples which we hope you will use in your
290       programs.  The examples may be freely copied, modified and distributed
291       for any purpose without any restrictions.
292

BUGS

294       To get a list of bugs against libguestfs, use this link:
295       https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools
296
297       To report a new bug against libguestfs, use this link:
298       https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools
299
300       When reporting a bug, please supply:
301
302       •   The version of libguestfs.
303
304       •   Where you got libguestfs (eg. which Linux distro, compiled from
305           source, etc)
306
307       •   Describe the bug accurately and give a way to reproduce it.
308
309       •   Run libguestfs-test-tool(1) and paste the complete, unedited output
310           into the bug report.
311
312
313
314libguestfs-1.50.1                 2023-02-21                  guestfs-ocaml(3)
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