Devicemapper 源码分析和流程，devicemapper源码
Devicemapper 源码分析和流程，devicemapper源码
整个流程大体如下： 
创建 thinpool
// This is theprogrammatic example of "dmsetup create"
funccreatePool(poolName string, dataFile, metadataFile *os.File, poolBlockSizeuint32) error {
...
params := fmt.Sprintf("%s %s %d 32768 1skip_block_zeroing", metadataFile.Name(), dataFile.Name(), poolBlockSize)
if err := task.AddTarget(0, size/512,"thin-pool", params); err != nil { return fmt.Errorf("Can't addtarget %s", err)
}
...
}
相当于执行下面的操作：
# dmsetup create docker-8:1-696417-pool--table ‗0 419430400 thin-pool 7:1 7:0 128 32768 1 skip_block_zeroing‘
# dmsetup table docker-8:1-696417-pool
0 419430400thin-pool 7:1 7:0 128 32768 1 skip_block_zeroing
创建 BaseImage
实际上，thin-provisionedvolume 分两步，首先是发送一个消息给 pool，创建一个 volume。然后激活
volume。只有 activated 的 volume，才能在 dmsetup info 的输出中看到。 （1）Creating a newthinly-provisioned volume funccreateDevice(poolName string, deviceId *int) error { … if err :=task.SetMessage(fmt.Sprintf("create_thin %d", *deviceId)); err != nil{ return fmt.Errorf("Can't set message %s", err) } 相当于执行下面的操作： #dmsetup message/dev/mapper/ docker-8:1-696417-pool 0 "create_thin 0"
///删除 thin volume(释放空间,删除(remove+delete)thin volume) func (devices *DeviceSet) DeleteDevice(hashstring) /// 将 thin volume 从 /var/lib/docker/devicemapper/mnt/$id umount, deactivate(remove )thinvolume(don't delete) func (devices*DeviceSet) UnmountDevice(hash string) ///activate thin volume ，然后 mount 到/var/lib/docker/devicemapper/mnt/$idfunc (devices *DeviceSet) MountDevice(hash, path, mountLabel string) ///thin pool 的统计信息(docker info) func (devices*DeviceSet) Status() *Status ///thin pool 初始化 funcNewDeviceSet(root string, doInit bool, options []string) Devmapper接口 devmapper/devmapper.go封装了 OS 层的 thin volume 的基本操作。 ///dmsetup suspend funcsuspendDevice(name string) ///dmsetup resume funcresumeDevice(name string) ///messagecreate_thin funccreateDevice(poolName string, deviceId *int) ///message delete funcdeleteDevice(poolName string, deviceId int) ///dmsetup remove funcremoveDevice(name string) ///dmsetup create funcactivateDevice(poolName string, name string, deviceId int, size uint64) ///message'create_snap' funccreateSnapDevice(poolName string, deviceId *int, baseName string, baseDeviceIdint) 三者之间的调用关系如下： 
查看 stop 的容器的文件系统
stop 的容器的 thin volume 都处于未激活（deactivate）状态，我们可以将其激活（activate），然后查 看文件系统中的内容。
我们创建一个容器，不启动：
# docker create --name="yy1" centos /bin/bash 93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9
metadata 下面新增两个目录：
# ls metadata/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e993f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9 -init
我们可以查看 thin volume 的信息
#cat metadata/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9{"device_id":5,"size":21474836480,"transaction_id":8,"initialized":false}
# catmetadata/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9 -init{"device_id":4,"size":21474836480,"transaction_id":7,"initialized":false}
我们来尝试手动挂载 thin volume，首先 activate thin volume： # dmsetup create 93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9 -init --table "0 41943040 thin 253:0 4" 然后就可以挂载该 thin volume 了： # mount /dev/mapper/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9-init mnt/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9-init # lsmnt/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9 -init/ id lost+foundrootfs deactivate thinvolume # umountmnt/93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9-init # dmsetup remove93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01 |
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