NAME¶

guestfs-examples - Examples of using libguestfs from C

SYNOPSIS¶

 #include <guestfs.h>
 
 guestfs_h *g = guestfs_create ();
 guestfs_add_drive_ro (g, "disk.img");
 guestfs_launch (g);
 cc prog.c -o prog -lguestfs
or:
 cc prog.c -o prog `pkg-config libguestfs --cflags --libs`

DESCRIPTION¶

This manual page contains examples of calling libguestfs from the C programming language. If you are not familiar with using libguestfs, you also need to read guestfs(3).

EXAMPLE 1: CREATE A DISK IMAGE¶

 /* Example showing how to create a disk image. */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <guestfs.h>
 
 int
 main (int argc, char *argv[])
 {
   guestfs_h *g;
   size_t i;
 
   g = guestfs_create ();
   if (g == NULL) {
     perror ("failed to create libguestfs handle");
     exit (EXIT_FAILURE);
  }
 
   /* Create a raw-format sparse disk image, 512 MB in size. */
   int fd = open ("disk.img", O_CREAT|O_WRONLY|O_TRUNC|O_NOCTTY, 0666);
   if (fd == -1) {
     perror ("disk.img");
     exit (EXIT_FAILURE);
   }
   if (ftruncate (fd, 512 * 1024 * 1024) == -1) {
     perror ("disk.img: truncate");
     exit (EXIT_FAILURE);
   }
   if (close (fd) == -1) {
     perror ("disk.img: close");
     exit (EXIT_FAILURE);
   }
 
   /* Set the trace flag so that we can see each libguestfs call. */
   guestfs_set_trace (g, 1);
 
   /* Add the disk image to libguestfs. */
   if (guestfs_add_drive_opts (g, "disk.img",
         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw", /* raw format */
         GUESTFS_ADD_DRIVE_OPTS_READONLY, 0, /* for write */
         -1) /* this marks end of optional arguments */
       == -1)
     exit (EXIT_FAILURE);
 
   /* Run the libguestfs back-end. */
   if (guestfs_launch (g) == -1)
     exit (EXIT_FAILURE);
 
   /* Get the list of devices.  Because we only added one drive
    * above, we expect that this list should contain a single
    * element.
    */
   char **devices = guestfs_list_devices (g);
   if (devices == NULL)
     exit (EXIT_FAILURE);
   if (devices[0] == NULL || devices[1] != NULL) {
     fprintf (stderr, "error: expected a single device from list-devices\n");
     exit (EXIT_FAILURE);
   }
 
   /* Partition the disk as one single MBR partition. */
   if (guestfs_part_disk (g, devices[0], "mbr") == -1)
     exit (EXIT_FAILURE);
 
   /* Get the list of partitions.  We expect a single element, which
    * is the partition we have just created.
    */
   char **partitions = guestfs_list_partitions (g);
   if (partitions == NULL)
     exit (EXIT_FAILURE);
   if (partitions[0] == NULL || partitions[1] != NULL) {
     fprintf (stderr, "error: expected a single partition from list-partitions\n");
     exit (EXIT_FAILURE);
   }
 
   /* Create a filesystem on the partition. */
   if (guestfs_mkfs (g, "ext4", partitions[0]) == -1)
     exit (EXIT_FAILURE);
 
   /* Now mount the filesystem so that we can add files. */
   if (guestfs_mount (g, partitions[0], "/") == -1)
     exit (EXIT_FAILURE);
 
   /* Create some files and directories. */
   if (guestfs_touch (g, "/empty") == -1)
     exit (EXIT_FAILURE);
   const char *message = "Hello, world\n";
   if (guestfs_write (g, "/hello", message, strlen (message)) == -1)
     exit (EXIT_FAILURE);
   if (guestfs_mkdir (g, "/foo") == -1)
     exit (EXIT_FAILURE);
 
   /* This one uploads the local file /etc/resolv.conf into
    * the disk image.
    */
   if (guestfs_upload (g, "/etc/resolv.conf", "/foo/resolv.conf") == -1)
     exit (EXIT_FAILURE);
 
   /* Because we wrote to the disk and we want to detect write
    * errors, call guestfs_shutdown.  You don't need to do this:
    * guestfs_close will do it implicitly.
    */
   if (guestfs_shutdown (g) == -1)
     exit (EXIT_FAILURE);
 
   guestfs_close (g);
 
   /* Free up the lists. */
   for (i = 0; devices[i] != NULL; ++i)
     free (devices[i]);
   free (devices);
   for (i = 0; partitions[i] != NULL; ++i)
     free (partitions[i]);
   free (partitions);
 
   exit (EXIT_SUCCESS);
 }

EXAMPLE 2: INSPECT A VIRTUAL MACHINE DISK IMAGE¶

 /* Inspect a disk image and display operating systems it may contain. */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <guestfs.h>
 
 static int
 compare_keys_len (const void *p1, const void *p2)
 {
   const char *key1 = * (char * const *) p1;
   const char *key2 = * (char * const *) p2;
   return strlen (key1) - strlen (key2);
 }
 
 static size_t
 count_strings (char *const *argv)
 {
   size_t c;
 
   for (c = 0; argv[c]; ++c)
     ;
   return c;
 }
 
 int
 main (int argc, char *argv[])
 {
   guestfs_h *g;
   const char *disk;
   char **roots, *root, *str, **mountpoints, **lines;
   size_t i, j;
 
   if (argc != 2) {
     fprintf (stderr, "usage: inspect_vm disk.img\n");
     exit (EXIT_FAILURE);
   }
   disk = argv[1];
 
   g = guestfs_create ();
   if (g == NULL) {
     perror ("failed to create libguestfs handle");
     exit (EXIT_FAILURE);
   }
 
   /* Attach the disk image read-only to libguestfs. */
   if (guestfs_add_drive_opts (g, disk,
      /* GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw", */
         GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
         -1) /* this marks end of optional arguments */
       == -1)
     exit (EXIT_FAILURE);
 
   /* Run the libguestfs back-end. */
   if (guestfs_launch (g) == -1)
     exit (EXIT_FAILURE);
 
   /* Ask libguestfs to inspect for operating systems. */
   roots = guestfs_inspect_os (g);
   if (roots == NULL)
     exit (EXIT_FAILURE);
   if (roots[0] == NULL) {
     fprintf (stderr, "inspect_vm: no operating systems found\n");
     exit (EXIT_FAILURE);
   }
 
   for (j = 0; roots[j] != NULL; ++j) {
     root = roots[j];
 
     printf ("Root device: %s\n", root);
 
     /* Print basic information about the operating system. */
     str = guestfs_inspect_get_product_name (g, root);
     if (str)
       printf ("  Product name: %s\n", str);
     free (str);
 
     printf ("  Version:      %d.%d\n",
             guestfs_inspect_get_major_version (g, root),
             guestfs_inspect_get_minor_version (g, root));
 
     str = guestfs_inspect_get_type (g, root);
     if (str)
       printf ("  Type:         %s\n", str);
     free (str);
     str = guestfs_inspect_get_distro (g, root);
     if (str)
       printf ("  Distro:       %s\n", str);
     free (str);
 
     /* 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.
      */
     mountpoints = guestfs_inspect_get_mountpoints (g, root);
     if (mountpoints == NULL)
       exit (EXIT_FAILURE);
 
     qsort (mountpoints, count_strings (mountpoints) / 2, 2 * sizeof (char *),
            compare_keys_len);
     for (i = 0; mountpoints[i] != NULL; i += 2) {
       /* Ignore failures from this call, since bogus entries can
        * appear in the guest's /etc/fstab.
        */
       guestfs_mount_ro (g, mountpoints[i+1], mountpoints[i]);
       free (mountpoints[i]);
       free (mountpoints[i+1]);
     }
     free (mountpoints);
 
     /* If /etc/issue.net file exists, print up to 3 lines. */
     if (guestfs_is_file (g, "/etc/issue.net") > 0) {
       printf ("--- /etc/issue.net ---\n");
       lines = guestfs_head_n (g, 3, "/etc/issue.net");
       if (lines == NULL)
         exit (EXIT_FAILURE);
       for (i = 0; lines[i] != NULL; ++i) {
         printf ("%s\n", lines[i]);
         free (lines[i]);
       }
       free (lines);
     }
 
     /* Unmount everything. */
     if (guestfs_umount_all (g) == -1)
       exit (EXIT_FAILURE);
 
     free (root);
   }
   free (roots);
 
   guestfs_close (g);
 
   exit (EXIT_SUCCESS);
 }

SEE ALSO¶

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

AUTHORS¶

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

COPYRIGHT¶

Copyright (C) 2010-2012 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.