16.11. 使用编程语言的 API

红帽企业 Linux 6.2 中的以下语言可直接使用 libguestfs API：C、C++、Perl、Python、Java、Ruby 和 OCaml。

要安装 C 和 C++ 绑定，请输入以下命令：
```
yum install libguestfs-devel
```
```
# yum install libguestfs-devel
```
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安装 Perl 绑定：
```
yum install 'perl(Sys::Guestfs)'
```
```
# yum install 'perl(Sys::Guestfs)'
```
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安装 Python 绑定：
```
yum install python-libguestfs
```
```
# yum install python-libguestfs
```
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安装 Java 绑定：

yum install libguestfs-java libguestfs-java-devel libguestfs-javadoc

# yum install libguestfs-java libguestfs-java-devel libguestfs-javadoc

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安装 Ruby 绑定：
```
yum install ruby-libguestfs
```
```
# yum install ruby-libguestfs
```
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安装 OCaml 绑定：

yum install ocaml-libguestfs ocaml-libguestfs-devel

# yum install ocaml-libguestfs ocaml-libguestfs-devel

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每个语言的绑定基本上相同，但具有细微变化。C 语句：

guestfs_launch (g);

guestfs_launch (g);

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在 Perl 中会出现以下内容：

$g->launch ()

$g->launch ()

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或者类似 OCaml 中的以下内容：

g#launch ()

g#launch ()

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本节仅包括 C 中的 API。

在 C 和 C++ 绑定中，您必须手动检查是否有错误。在其他绑定中，错误会被转换为例外。以下示例中显示的其他错误检查不需要其他语言，但您可能希望添加代码来捕获异常。有关 libguestfs API 架构的一些关注点，请参考以下列表：

libguestfs API 是同步的。每个调用块直到完成为止。如果要异步调用，您必须创建线程。
libguestfs API 不是线程安全：每个句柄应该只从一个线程使用，或者您希望在线程之间共享一个进程，您应该实施自己的 mutex，以确保两个线程无法同时在一个进程上执行命令。
您不应该在同一磁盘镜像中打开多个句柄。如果所有句柄都是只读的，但仍然不建议这样做。
如果其他部分可能正在使用该磁盘镜像（例如，实时虚拟机），您不应该添加磁盘镜像来写入。执行此操作将导致磁盘损坏。
在当前使用（例如，实时虚拟机）的磁盘镜像上打开只读句柄；但是，如果磁盘映像在读取时大量写入该磁盘镜像时，结果可能会无法预测或不一致。

16.11.1. 通过 C 程序与 API 交互
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您的 C 程序应该首先包括 {s.> 标头文件并创建一个句柄：

#include <stdio.h>
#include <stdlib.h>
#include <guestfs.h>

int
main (int argc, char *argv[])
{
  guestfs_h *g;

  g = guestfs_create ();
  if (g == NULL) {
    perror ("failed to create libguestfs handle");
    exit (EXIT_FAILURE);
   }

   /* ... */

   guestfs_close (g);

   exit (EXIT_SUCCESS);
 }

#include <stdio.h>
#include <stdlib.h>
#include <guestfs.h>

int
main (int argc, char *argv[])
{
  guestfs_h *g;

  g = guestfs_create ();
  if (g == NULL) {
    perror ("failed to create libguestfs handle");
    exit (EXIT_FAILURE);
   }

   /* ... */

   guestfs_close (g);

   exit (EXIT_SUCCESS);
 }

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将此程序保存到文件(test.c)。编译这个程序并使用以下两个命令运行它：

gcc -Wall test.c -o test -lguestfs
./test

gcc -Wall test.c -o test -lguestfs
./test

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在这个阶段，应该打印没有输出。本节的其余部分演示了演示了如何扩展此程序以创建新磁盘镜像、对它进行分区，将其格式化为 ext4 文件系统，并在文件系统中创建一些文件。磁盘映像将命名为 disk.img，并在当前目录中创建。

这个程序概述如下：

创建句柄。
将磁盘添加到句柄。
启动 libguestfs 后端。
创建分区、文件系统和文件。
关闭句柄并退出。

以下是修改的程序：

#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);

   /* Set the autosync flag so that the disk will be synchronized
    * automatically when the libguestfs handle is closed.
    */
   guestfs_set_autosync (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 an ext4 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_options (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 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 'autosync' was set (above) we can just close the handle
    * and the disk contents will be synchronized.  You can also do
    * this manually by calling guestfs_umount_all and guestfs_sync.
    */
   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);
 }

#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);

   /* Set the autosync flag so that the disk will be synchronized
    * automatically when the libguestfs handle is closed.
    */
   guestfs_set_autosync (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 an ext4 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_options (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 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 'autosync' was set (above) we can just close the handle
    * and the disk contents will be synchronized.  You can also do
    * this manually by calling guestfs_umount_all and guestfs_sync.
    */
   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);
 }

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使用以下两个命令编译并运行该程序：

gcc -Wall test.c -o test -lguestfs
./test

gcc -Wall test.c -o test -lguestfs
./test

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如果程序成功完成，您应该使用名为 disk.img 的磁盘镜像（可以使用 guestfish 检查）来保留它：

guestfish --ro -a disk.img -m /dev/sda1
><fs> ll /
><fs> cat /foo/resolv.conf

guestfish --ro -a disk.img -m /dev/sda1
><fs> ll /
><fs> cat /foo/resolv.conf

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默认情况下（仅用于 C 和 C++ 绑定），libguestfs 会将错误打印到 stderr。您可以通过设置错误处理程序来更改此行为。guestfs(3)man page 详细阐述此问题。

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16.11. 使用编程语言的 API

16.11.1. 通过 C 程序与 API 交互
复制链接

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16.11.1. 通过 C 程序与 API 交互
复制链接