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guestfs-golang(3) Virtualization Support guestfs-golang(3)

NAME

guestfs-golang - How to use libguestfs from Go

SYNOPSIS

 import "libguestfs.org/guestfs"
 
 g, errno := guestfs.Create ()
 if errno != nil {
     panic (fmt.Sprintf ("could not create handle: %s", errno))
 }
 defer g.Close ()
 if err := g.Add_drive ("test.img"); err != nil {
     panic (err)
 }
 if err := g.Launch (); err != nil {
     panic (err)
 }
 if err := g.Shutdown (); err != nil {
     panic (err)
 }

DESCRIPTION

This manual page documents how to call libguestfs from the Go 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).

IMPORTING THE MODULE

The module is called "guestfs". The full package name to import is "libguestfs.org/guestfs".

CREATING AND CLOSING THE HANDLE

Use either "guestfs.Create" or "guestfs.Create_flags" to create the handle. The handle is closed implicitly if it is garbage collected. However it is probably a good idea to close it explicitly, either by calling "g.Close ()" or by deferring the same.

ERRORS

"guestfs.Create" and "guestfs.Create_flags" return a simple *error, which is really just a C "errno" wrapped up in the appropriate golang struct.

All other calls return a *GuestfsError which (if non-nil) is a richer struct that contains the error string from libguestfs, the errno (if available) and the operation which failed. This can also be converted to a string for display.

LIMITATIONS

  • No support for events (see "EVENTS" in guestfs(3)).
  • UUIDs are not returned in structures.

EXAMPLE 1: CREATE A DISK IMAGE

 /* Example showing how to create a disk image. */
 
 package main
 
 import (
        "fmt"
        "libguestfs.org/guestfs"
 )
 
 func main() {
        output := "disk.img"
 
        g, errno := guestfs.Create ()
        if errno != nil {
                panic (errno)
        }
        defer g.Close ()
 
        /* Create a raw-format sparse disk image, 512 MB in size. */
        if err := g.Disk_create (output, "raw", 512 * 1024 * 1024); err != nil {
                panic (err)
        }
 
        /* Set the trace flag so that we can see each libguestfs call. */
        g.Set_trace (true)
 
        /* Attach the disk image to libguestfs. */
        optargs := guestfs.OptargsAdd_drive{
                Format_is_set: true,
                Format: "raw",
                Readonly_is_set: true,
                Readonly: false,
        }
        if err := g.Add_drive (output, &optargs); err != nil {
                panic (err)
        }
 
        /* Run the libguestfs back-end. */
        if err := g.Launch (); err != nil {
                panic (err)
        }
 
        /* Get the list of devices.  Because we only added one drive
         * above, we expect that this list should contain a single
         * element.
         */
        devices, err := g.List_devices ()
        if err != nil {
                panic (err)
        }
        if len(devices) != 1 {
                panic ("expected a single device from list-devices")
        }
 
        /* Partition the disk as one single MBR partition. */
        err = g.Part_disk (devices[0], "mbr")
        if err != nil {
                panic (err)
        }
 
        /* Get the list of partitions.  We expect a single element, which
         * is the partition we have just created.
         */
        partitions, err := g.List_partitions ()
        if err != nil {
                panic (err)
        }
        if len(partitions) != 1 {
                panic ("expected a single partition from list-partitions")
        }
 
        /* Create a filesystem on the partition. */
        err = g.Mkfs ("ext4", partitions[0], nil)
        if err != nil {
                panic (err)
        }
 
        /* Now mount the filesystem so that we can add files. */
        err = g.Mount (partitions[0], "/")
        if err != nil {
                panic (err)
        }
 
        /* Create some files and directories. */
        err = g.Touch ("/empty")
        if err != nil {
                panic (err)
        }
        message := []byte("Hello, world\n")
        err = g.Write ("/hello", message)
        if err != nil {
                panic (err)
        }
        err = g.Mkdir ("/foo")
        if err != nil {
                panic (err)
        }
 
        /* This one uploads the local file /etc/resolv.conf into
         * the disk image.
         */
        err = g.Upload ("/etc/resolv.conf", "/foo/resolv.conf")
        if err != nil {
                panic (err)
        }
 
        /* 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.
         */
        if err = g.Shutdown (); err != nil {
                panic (fmt.Sprintf ("write to disk failed: %s", err))
        }
 }

EXAMPLE 2: INSPECT A VIRTUAL MACHINE DISK IMAGE

 /* Example showing how to inspect a virtual machine disk. */
 
 package main
 
 import (
        "fmt"
        "os"
        "libguestfs.org/guestfs"
 )
 
 func main() {
        if len(os.Args) < 2 {
                panic ("usage: inspect-vm disk.img")
        }
        disk := os.Args[1]
 
        g, errno := guestfs.Create ()
        if errno != nil {
                panic (fmt.Sprintf ("could not create handle: %s", errno))
        }
 
        /* Attach the disk image read-only to libguestfs. */
        optargs := guestfs.OptargsAdd_drive{
                Format_is_set: true,
                Format: "raw",
                Readonly_is_set: true,
                Readonly: true,
        }
        if err := g.Add_drive (disk, &optargs); err != nil {
                panic (err)
        }
 
        /* Run the libguestfs back-end. */
        if err := g.Launch (); err != nil {
                panic (err)
        }
 
        /* Ask libguestfs to inspect for operating systems. */
        roots, err := g.Inspect_os ()
        if err != nil {
                panic (err)
        }
        if len(roots) == 0 {
                panic ("inspect-vm: no operating systems found")
        }
 
        for _, root := range roots {
                fmt.Printf ("Root device: %s\n", root)
 
                /* Print basic information about the operating system. */
                s, _ := g.Inspect_get_product_name (root)
                fmt.Printf ("  Product name: %s\n", s)
                major, _ := g.Inspect_get_major_version (root)
                minor, _ := g.Inspect_get_minor_version (root)
                fmt.Printf ("  Version:      %d.%d\n", major, minor)
                s, _ = g.Inspect_get_type (root)
                fmt.Printf ("  Type:         %s\n", s)
                s, _ = g.Inspect_get_distro (root)
                fmt.Printf ("  Distro:       %s\n", s)
 
                /* XXX Incomplete example.  Sorting the keys by length
                 * is unnecessarily hard in golang.
                 */
        }
 }

SEE ALSO

guestfs(3), guestfs-examples(3), guestfs-erlang(3), guestfs-gobject(3), guestfs-java(3), guestfs-lua(3), guestfs-ocaml(3), guestfs-perl(3), guestfs-python(3), guestfs-recipes(1), guestfs-ruby(3), http://www.golang.org/, http://libguestfs.org/.

AUTHORS

Richard W.M. Jones ("rjones at redhat dot com")

COPYRIGHT

Copyright (C) 2013 Red Hat Inc.

LICENSE

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.

BUGS

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.
2020-03-09 libguestfs-1.42.0