mount一个lvm格式的磁盘映像文件

如果是非lvm格式的，则非常方便，给mount命令传递offset参数即可，例如：
[root@jcwkyl xen-images]# fdisk -lu centos_vm1
last_lba(): I don't know how to handle files with mode 81ed
You must set cylinders.
You can do this from the extra functions menu.

Disk centos_vm1: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes

      Device Boot      Start         End      Blocks   Id  System
centos_vm1p1   *          63      208844      104391   83  Linux
centos_vm1p2          208845     4192964     1992060   8e  Linux LVM
看到第一个磁盘分区是Linux分区，起始于63扇区，直接mount：
[root@jcwkyl xen-images]# mkdir -p /mnt/disk
[root@jcwkyl xen-images]# mount -o loop,offset=$[63*512] centos_vm1 /mnt/disk/
[root@jcwkyl xen-images]# ls /mnt/disk/
config-2.6.18-92.el5xen      lost+found                   System.map-2.6.18-92.el5xen  xen-syms-2.6.18-92.el5
grub                         message                      vmlinuz-2.6.18-92.el5xen
initrd-2.6.18-92.el5xen.img  symvers-2.6.18-92.el5xen.gz  xen.gz-2.6.18-92.el5
显示，这个linux分区是/boot，root文件系统在centos_vm1p2的这块lvm区中，要设法把它mount上来，使用以下方法：

首先找到它的起始偏移，使用fdisk的-u参数在列出磁盘分区的时候以扇区(sector)为单位，否则是以柱面(cylinder)为单位的：
[root@jcwkyl xen-images]# fdisk -lu centos_vm1
last_lba(): I don't know how to handle files with mode 81ed
You must set cylinders.
You can do this from the extra functions menu.

Disk centos_vm1: 0 MB, 0 bytes
255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes

      Device Boot      Start         End      Blocks   Id  System
centos_vm1p1   *          63      208844      104391   83  Linux
centos_vm1p2          208845     4192964     1992060   8e  Linux LVM

从上看出lvm分区起始于208845扇区，把这个地址处的分区mount为loop设备：
-f参数表示自动寻找可用的loop设备文件，-o指定偏移量。
[root@jcwkyl xen-images]# losetup -f -o $[208845*512] centos_vm1
[root@jcwkyl xen-images]# losetup -a
/dev/loop0: [0806]:1097730 (centos_vm1), offset 106928640

扫描lvm volumns:
[root@jcwkyl xen-images]# lvm pvscan
  PV /dev/loop0   VG VolGroup00   lvm2 [1.88 GB / 0    free]
  Total: 1 [1.88 GB] / in use: 1 [1.88 GB] / in no VG: 0 [0   ]

激活lvm volumn:
[root@jcwkyl xen-images]# lvm vgchange -ay
  2 logical volume(s) in volume group "VolGroup00" now active
[root@jcwkyl xen-images]# ls /dev/mapper/
control  VolGroup00-LogVol00  VolGroup00-LogVol01
[root@jcwkyl xen-images]# lvm lvs
  LV       VG         Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  LogVol00 VolGroup00 -wi-a-   1.50G                                     
  LogVol01 VolGroup00 -wi-a- 384.00M                            

使用：      
[root@jcwkyl xen-images]# mount /dev/mapper/VolGroup00-LogVol00 /mnt/usb
[root@jcwkyl xen-images]# ls /mnt/usb
bin   dev  home  lost+found  misc  opt       proc  sbin     srv  tmp  var
boot  etc  lib   media       mnt   poweroff  root  selinux  sys  usr

最后，在操作完以后，umount这个设备，然后设置这个lvm volumn为非活动状态：
[root@jcwkyl xen-images]# umount /mnt/usb
[root@jcwkyl xen-images]# lvm vgchange -an
  0 logical volume(s) in volume group "VolGroup00" now active
[root@jcwkyl xen-images]# losetup -a
/dev/loop0: [0806]:1097730 (centos_vm1), offset 106928640
[root@jcwkyl xen-images]# losetup -d /dev/loop0