已知xen的各dom之间通过xenstore共享配置信息。
so，先装上xenstore-utils
加载xenfs，并挂载到/proc/xen路径下。
root@ip-172-31-26-60:~# modprobe xenfs root@ip-172-31-26-60:~# mount -t xenfs none /proc/xen/
然后就可以读取dom配置信息了。
由于权限问题。这里只能读自己的。
root@ip-172-31-26-60:~# xenstore-read domid 1505 root@ip-172-31-26-60:~# xenstore-ls /local/domain/1505 vm = "/vm/ec22d790-58e6-6c14-51f6-44eacf17feef" device = "" vbd = "" 2049 = "" virtual-device = "2049" device-type = "disk" protocol = "x86_64-abi" backend-id = "0" state = "4" backend = "/local/domain/0/backend/vbd/1505/2049" ring-ref = "8" event-channel = "9" 2064 = "" virtual-device = "2064" device-type = "disk" protocol = "x86_64-abi" backend-id = "0" state = "4" backend = "/local/domain/0/backend/vbd/1505/2064" ring-ref = "9" event-channel = "10" 2080 = "" virtual-device = "2080" device-type = "disk" protocol = "x86_64-abi" backend-id = "0" state = "4" backend = "/local/domain/0/backend/vbd/1505/2080" ring-ref = "10" event-channel = "11" 2051 = "" virtual-device = "2051" device-type = "disk" protocol = "x86_64-abi" backend-id = "0" state = "4" backend = "/local/domain/0/backend/vbd/1505/2051" ring-ref = "11" event-channel = "12" vif = "" 0 = "" mac = "0a:a7:3f:42:b3:e9" handle = "0" protocol = "x86_64-abi" backend-id = "0" state = "4" backend = "/local/domain/0/backend/vif/1505/0" tx-ring-ref = "12" rx-ring-ref = "768" event-channel = "13" request-rx-copy = "1" feature-rx-notify = "1" feature-sg = "1" feature-gso-tcpv4 = "1" console = "" 0 = "" protocol = "x86_64-abi" state = "1" backend-id = "0" backend = "/local/domain/0/backend/console/1505/0" control = "" platform-feature-multiprocessor-suspend = "1" error = "" memory = "" target = "1740800" guest = "" hvmpv = "" data = "" device-misc = "" vif = "" nextDeviceID = "1" console = "" nextDeviceID = "1" console = "" ring-ref = "4595562" port = "2" limit = "1048576" type = "xenconsoled" tty = "/dev/pts/27" name = "dom_1813114895" domid = "1505" cpu = "" 0 = "" availability = "online" store = "" ring-ref = "4595563" port = "1" serial = "" 0 = "" tty = "/dev/pts/27"
这里可以看到磁盘、网卡等设备。
再看几个磁盘
root@ip-172-31-26-60:~# xenstore-ls /local/domain/0/backend/vbd/1505/2049 domain = "dom_1813114895" frontend = "/local/domain/1505/device/vbd/2049" uuid = "b3547591-292e-f124-6ecf-d579a3dcfbf7" bootable = "1" dev = "sda1" state = "4" params = "/dev/xgnbd925" mode = "w" removable = "1" online = "1" frontend-id = "1505" type = "phy" max-ring-pages = "1" physical-device = "fc:39d" hotplug-status = "connected" sectors = "16777216" info = "0" sector-size = "512" root@ip-172-31-26-60:~# xenstore-ls /local/domain/0/backend/vbd/1505/2064 domain = "dom_1813114895" frontend = "/local/domain/1505/device/vbd/2064" uuid = "aa44ee16-71dd-0fdf-3963-01d9d0235de6" bootable = "0" dev = "sdb" state = "4" params = "/dev/mapper/cow-VolGroupDomU-instance_ephemeral_store_24" mode = "w" removable = "1" online = "1" frontend-id = "1505" type = "phy" max-ring-pages = "1" physical-device = "fd:9c" hotplug-status = "connected" sectors = "312705024" info = "0" sector-size = "512" root@ip-172-31-26-60:~# xenstore-ls /local/domain/0/backend/vbd/1505/2080 domain = "dom_1813114895" frontend = "/local/domain/1505/device/vbd/2080" uuid = "8b297bf6-fa19-513a-dad3-4782bab750f5" bootable = "0" dev = "sdc" state = "4" params = "/dev/xgnbd317" mode = "w" removable = "1" online = "1" frontend-id = "1505" type = "phy" max-ring-pages = "1" physical-device = "fc:13d" hotplug-status = "connected" sectors = "4194304" info = "0" sector-size = "512" root@ip-172-31-26-60:~# xenstore-ls /local/domain/0/backend/vbd/1505/2051 domain = "dom_1813114895" frontend = "/local/domain/1505/device/vbd/2051" uuid = "6eb3cab4-b007-dba0-3e5a-6204361fec4f" bootable = "0" dev = "sda3" state = "4" params = "/dev/VolGroupDomU/instance_swap_store_24" mode = "w" removable = "1" online = "1" frontend-id = "1505" type = "phy" max-ring-pages = "1" physical-device = "fd:64" hotplug-status = "connected" sectors = "1835008" info = "0" sector-size = "512"
可以看到ebs磁盘sda1(xvda1,root)、sda3(xvda3,swap)、sdc是由amazon修改的gnbd变种xgnbd实现。
而sdb(instance store 0:ephemeral0)则由lvm实现。
测试过程中竟然出现了dns nameserver没有配置好的情况，看来ec2也不像传说中那般神奇啊。
============ 2013.12.18 补充 =============
官方镜像都是基于ebs的。
而社区镜像里还有一种root(sda1)为Instance store的镜像。
root@ip-172-31-30-64:~# xenstore-ls /local/domain/0/backend/vbd/1581/2049 domain = "dom_1821728485" frontend = "/local/domain/1581/device/vbd/2049" uuid = "4c382ca3-d5b1-39f0-67c5-60758cac32f5" bootable = "1" dev = "sda1" state = "4" params = "/mnt/instance_image_store_12/1751320884" mode = "w" removable = "1" online = "1" frontend-id = "1581" type = "file" max-ring-pages = "1" node = "/dev/loop16" physical-device = "7:10" hotplug-status = "connected" sectors = "20971520" info = "0" sector-size = "512"
可见这种镜像是通过loop实现的虚拟块设备，既然是loop则社区镜像是raw格式。
这种Instance store的系统镜像只有9.9G，其他空间则通过sda2(xvda2)挂载到/mnt的形式提供，和swap一起都是lvm的后端实现，但是不知这块空的数据盘为毛是cow，也不知这个_netdev是哪来的，fstab里没有的啊。
ubuntu@ip-172-31-29-253:/mnt$ mount /dev/xvda1 on / type ext4 (rw) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) none on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) udev on /dev type devtmpfs (rw,mode=0755) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755) none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880) none on /run/shm type tmpfs (rw,nosuid,nodev) /dev/xvda2 on /mnt type ext3 (rw,_netdev) ubuntu@ip-172-31-29-253:/mnt$ df -h Filesystem Size Used Avail Use% Mounted on /dev/xvda1 9.9G 775M 8.6G 9% / udev 819M 12K 819M 1% /dev tmpfs 331M 168K 331M 1% /run none 5.0M 0 5.0M 0% /run/lock none 827M 0 827M 0% /run/shm /dev/xvda2 147G 188M 140G 1% /mnt ubuntu@ip-172-31-29-253:/mnt$ cat /etc/fstab LABEL=cloudimg-rootfs / ext4 defaults 0 0 /dev/xvda2 /mnt auto defaults,nobootwait,comment=cloudconfig 0 2 /dev/xvda3 none swap sw,comment=cloudconfig 0 0 ubuntu@ip-172-31-29-253:/mnt$
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