Devicemapper Source Analysis and process

The overall process is as follows: 650) this.width=650; "id=" aimg_1027 "src=" http://bbs.superwu.cn/data/attachment/forum/201506/05/ 152157z0b6rx7x68hidhdz.jpg "class=" Zoom "width=" "style=" border:none; "/> Create 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) } ... } is equivalent to performing the following actions: # Dmsetup Create docker-8:1-696417-pool--table 0 419430400 thin-pool 7:1 7:0 1 32768 ' # Dmsetup Table Docker-8:1-696417-pool 0 419430400thin-pool 7:1 7:0 32768 1 skip_block_zeroing Create baseimage In fact, Thin-provisionedvolume in two steps, the first is to send a message to the pool and create a volume. Then activate Volume Only activated volume can be seen in the output of Dmsetup info. (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) } is equivalent to performing the following actions: #dmsetup message/dev/mapper/docker-8:1-696417-pool 0 "Create_thin 0" TD width= "Style=" PADDING:4PX; >      # hexdump-c/var/lib/docker/devicemapper/metadata/base    00000000   &NBSP,    7b             []       5f 69 3a             |{" device_id ": 0," |       00000010   &NBSP,          7a +             3a       34       |size ": 2147483648|    00000020 30 2c 22 74 72 61 6e 73 61 63 74 69 6f 6e 5f 69 |, "transaction_i| 00000030 64 22 3a 31 2c 22 69 6e 69 74 69 61 6c 69 7a 65 |d ": 1," initialize| 00000040 64 22 3a 74 72 75 65 7d |d ": true}| You can see that base's device_id is 0. (2) activatedthinly-provisioned volumes Funcactivatedevice (poolname string, name string, deviceId int, size UInt64) error { ... Params: =fmt. Sprintf ("%s%d", poolname, DeviceId) If Err: = task. AddTarget (0, size/512, "thin", params); Err! = Nil {return FMT. Errorf ("Can ' t addtarget%s", err) } is equivalent to performing the following actions: #dmsetup createdocker-8:1-696417-base--table "0 41943040 thin/dev/mapper/docker-8:1-696417-pool 0" #dmsetup table docker-8:1-696417-base 0 41943040 thin 253:0 0 Only activated volume can be seen in the output of Dmsetup info. Basic operation of Devicemapper Driver The basic Operation /// Clear Thin Pool Func (d *driver) Cleanup () When loading a new image, add a new thin volume,id to Containerid or imageID func (d *driver) Create (ID, parent string) Mount thin volume to/var/lib/docker/devicemapper/mnt/$id directory (Docker start) func (d *driver) Get (ID, mountlabelstring) From/var/lib/docker/devicemapper/mnt/$id directory Umount thinvolume (Docker stop) func (d *driver) Put (ID string) /// Delete Volume ( true Delete ) Func (d *driver) Remove (ID string) Thinpool The basic Operation /// in the Thin Pool to create a new Snapshot Volume Func (Devices*deviceset) AddDevice (hash, basehash string) Delete Thin volume (free space, delete (remove+delete) thin volume) func (Devices *deviceset) Deletedevice (hashstring) Thin volume from/var/lib/docker/devicemapper/mnt/$id umount, deactivate (remove) Thinvolume (don ' t delete) Func (Devices*deviceset) Unmountdevice (hash string) Activate thin volume, then mount to/var/lib/docker/devicemapper/mnt/$idfunc (Devices *deviceset) mountdevice (hash, path , Mountlabel String) ///thin Pool the statistical information (Docker info) Func (Devices*deviceset) Status () *status ///thin Pool Initialize Funcnewdeviceset (Root string, doinit bool, options []string) Devmapper Interface Devmapper/devmapper.go encapsulates the OS layer of Thin Volume the basic operation. 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) The call relationships between the three are as follows: 650) this.width=650; "id=" aimg_1028 "src=" http://bbs.superwu.cn/data/attachment/forum/201506/05/ 152157iu095b5c8t2pf05b.jpg "class=" Zoom "width=" "style=" border:none; "/> View the file system of the Stop container The thin volume of the Stop container is in an inactive (deactivate) state, and we can activate it (activate) and view the contents of the file system. We create a container that does not start: # Docker Create--name= "Yy1" Centos/bin/bash 93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9 Metadata two new directories are added below: # ls metadata/ 93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e993f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01a D89f8e9-init we can view Thin Volume of information #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} Let's try to mount the thin volume manually, first activate thin volume: # Dmsetup Create 93f595ea79a0420cc263d054d3e63b5ad1e4cc3da128167984a6ac01ad89f8e9-init --table "0 41943040 Thin 253:0 4 " Then you can mount the thin volume: # 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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Devicemapper source Analysis and Flow