Xen创建虚拟机 loop device 数目限制问题

Ubuntu 14 默认对 loop devices 支持的最大数目是8，所以当我创建第九个虚拟机的时候，出现了下面的错误：

Parsing config from /home/ye/ubuntu-pv/ubuntu-pv-9/ubuntu-pv-9.cfglibxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: /etc/xen/scripts/block add [7615] exited with error status 1libxl: error: libxl_device.c:1138:device_hotplug_child_death_cb: script: Failed to find an unused loop devicelibxl: error: libxl_create.c:1176:domcreate_launch_dm: unable to add disk deviceslibxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: /etc/xen/scripts/block remove [7668] exited with error status 1libxl: error: libxl_device.c:1138:device_hotplug_child_death_cb: script: /etc/xen/scripts/block failed; error detected.libxl: error: libxl.c:1610:libxl__destroy_domid: non-existant domain 22libxl: error: libxl.c:1568:domain_destroy_callback: unable to destroy guest with domid 22libxl: error: libxl.c:1495:domain_destroy_cb: destruction of domain 22 failed

查看一下当前正在使用的的 loop devices：

root@ccrfox141:/home/ye/ubuntu-pv/ubuntu-pv-9# losetup -a/dev/loop0: [0804]:79497528 (/home/ye/ubuntu-pv/ubuntu-pv-1/ubuntu-pv-1.img)/dev/loop1: [0804]:79497536 (/home/ye/ubuntu-pv/ubuntu-pv-2/ubuntu-pv-2.img)/dev/loop2: [0804]:79497539 (/home/ye/ubuntu-pv/ubuntu-pv-3/ubuntu-pv-3.img)/dev/loop3: [0804]:79497546 (/home/ye/ubuntu-pv/ubuntu-pv-4/ubuntu-pv-4.img)/dev/loop4: [0804]:79497552 (/home/ye/ubuntu-pv/ubuntu-pv-5/ubuntu-pv-5.img)/dev/loop5: [0804]:79497556 (/home/ye/ubuntu-pv/ubuntu-pv-6/ubuntu-pv-6.img)/dev/loop6: [0804]:79497564 (/home/ye/ubuntu-pv/ubuntu-pv-7/ubuntu-pv-7.img)/dev/loop7: [0804]:79497570 (/home/ye/ubuntu-pv/ubuntu-pv-8/ubuntu-pv-8.img)

在 Ubuntu/Debian 上修改默认 loop devices 最大限制数目：

# echo 'options loop max_loop=128' >/etc/modprobe.d/loopdev

在 CentOS/RHEL 6 系统上更改 loop 最大数目更容易，最多支持256个，还不用重启：

# MAKEDEV -v /dev/loop

不过上面更改重启就会消失，所以把上面命令要加到 /etc/rc.local 里：

# vi /etc/rc.local...MAKEDEV -v /dev/loop

参考自：https://www.vpsee.com/2009/09/increase-the-number-of-configured-loop-devices/