Introduction to Tizen Platform - SKKUnyx.skku.ac.kr/wp-content/uploads/2016/03/Lecture6-Week9.pdf · 2016-05-03 · 36 5 Embedded Software Lab. • The oldest form of UNIX IPC and

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Embedded Software Lab.

Sungkyunkwan University


Dongkun Shin

전공핵심실습1:운영체제론Chapter 6. Inter-process Communication

(IPC)

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• Linux Kernel IPC– Pipe

– FIFO

– System V IPC

• Semaphore

• Message Queue

• Shared Memory

• Tizen Platform IPC– D-Bus

– vconf

Contents

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• Pipe

• FIFO

• System V IPC– Semaphore

– Message Queue

– Shared Memory

Linux Kernel IPC

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• User uses IPC mechanism via system calls provided by the kernel

IPC System Call

Linux Kernel

IPC System Call

PIPE (42)PIPE2 (359)

OPEN (5)READ (3)WRITE (4)

SEMGET (299)SEMOP (298)

MSGGET (303)MSGSND (301)MSGRCV (302)

SHMGET (307)SHMAT (305)SHMDT (306)

Tizen IPC System Calls (# syscall number)

PIPE Semaphore Message Queue Shared MemoryFIFO

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• The oldest form of UNIX IPC and provided by all unix systems

• Two limitations– Half-duplex : data flows only in one direction

– Can be used only between processes that have a common ancestor

• Usually used between the parent and child processes

• int pipe (int fd[2]);– Two file descriptors are returned through the fd argument

• fd[0] : open for reading

• fd[1] : open for writing

– The output of fd[1] is the input for fd[0]

PIPE

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PIPE (cont.)

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PIPE (cont.)

• Kernel Implementation (linux/fs/pipe.c)

SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags){

struct file *files[2];int fd[2];int error;

error = __do_pipe_flags(fd, files, flags);if (!error) {

if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {fput(files[0]);fput(files[1]);put_unused_fd(fd[0]);put_unused_fd(fd[1]);error = -EFAULT;

} else {fd_install(fd[0], files[0]);fd_install(fd[1], files[1]);

}}return error;

}

create 2 pipe files (later in fifo) and open with O_RDONLY and O_WRONLY flags

Copy file descriptors to userspace as an output of the system call

Install file *s in the file descriptor table of the process

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• Unrelated processes can exchange data, whereas pipes can be used only between related processes

• FIFO is a type of file. (S_ISFIFO macro against st_mode)

– FIFO is handled by file operations such as open(), close(), read(), and write(), once a FIFO created.

– Multiple readers/writers are allowed

• int mkfifo (const char *path, mode_t mode)– Generates FIFO with specific file name, path.

– Accesses the generated FIFO with open system calls between 2 processes

• open(“fifo1”, O_RDONLY) FIFO must have Reader / Writer both.

• open(“fifo1”, O_WRONLY)

FIFO (a.k.a named pipe)

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Create Pipe Files

• Create a directory entry

• Create an inode

• Plug pipefifo_ops to file_operations of the generated pipe or fifo files.

const struct file_operations pipefifo_fops = {.open = fifo_open,.llseek = no_llseek,.read = do_sync_read,.aio_read = pipe_read,.write = do_sync_write,.aio_write = pipe_write,.poll = pipe_poll,.unlocked_ioctl = pipe_ioctl,.release = pipe_release,.fasync = pipe_fasync,

};once pipefifo_fops is registered as file_operations,

the normal file I/O functions all work with FIFO

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• In Shell$ cat /proc/meminfo | grep –I active | tail –n4 > memory.txt

FIFO Example

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• Semaphore, Message Queue, and Shared Memory

• Semaphore– Synchronize itself with other processes

• Message Queue (Not equal to POSIX Message queue)

– Send or receive messages each other

• Shared Memory– Share a memory area

• System V IPCs shares same kernel data structures and operations (linux/ipc/util.h)– All IPC objects are stored in kernel memory

– They are referred to by IPC object identifier

– Kernel translate a given key to corresponding ID, whereas processes only can access the key

System V IPC

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• Key of IPC Resources– semget() – Get Semaphores IPC Resources

– msgget() – Get Messages IPC Resources

– shmget() – Get Share Memory IPC Resources

IPC Identifier

semget()msgget() + IPC Identifier

shmget() (XXX)

Process1 Process2

Some data for share

IPC resource

XXX

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IPC Resource (include/linux/ipc_namespace.h)

ipc_ids

represent

IPC Resources Type

kern_ipc_prem

represent

IPC Resource

kern_ipc_prem

represent

IPC Resource

kern_ipc_prem

represent

IPC Resource

struct idr ipcs_idr

The data structure similar with radix tree

to map a id to the corresponding pointer

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• Similar to the kernel semaphores (lock) – include/linux/semaphore.h, kernel/locking/semaphore.c

• Counters used to controlled access to shared data structures for multiple processes

Semaphore

Process

Some data for share

IPC resource

semget() : get IPC Identifier

semop() : Decrease or Increase semaphore count

semop( struct sembuf )

struct sembuf

sem_num : Semaphore number

sem_op : Add this to semval

(increase / decrease semaphore count)

sem_flg : Operation flags

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• Kernel Implementation

Semaphore (ipc/sem.c)

SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg){

struct ipc_namespace *ns;struct ipc_ops sem_ops;struct ipc_params sem_params;

ns = current->nsproxy->ipc_ns;

if (nsems < 0 || nsems > ns->sc_semmsl)return -EINVAL;

sem_ops.getnew = newary;sem_ops.associate = sem_security;sem_ops.more_checks = sem_more_checks;

sem_params.key = key;sem_params.flg = semflg;sem_params.u.nsems = nsems;

return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);}

newary() function allocates new ipc semaphore to ids as invoked via ipcget()

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newary() (ipc/sem.c)

ipc_ids

represent

IPC Resources Type

struct idr ipcs_idr

kern_ipc_prem

represent

IPC Resources

sem_array

represent

Semephore

kern_ipc_prem

represent

IPC Resources

sem_array

represent

Semephore

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• IPC Messages– msgget() : Create IPC Messages resources or get IPC identifier

– msgsnd() : Send messages

– msgrcv() : Receive messages

– POSIX Message Queue is implemented independently

Message Queue

Process1 Process2

Some data for share

IPC resource

XXX

msgsnd()

Buffer Data msgrcv()

Buffer Data

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• Kernel Implementation (ipc/msg.c)

Messages IPC Resources

SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg){

struct ipc_namespace *ns;struct ipc_ops msg_ops;struct ipc_params msg_params;


msg_ops.getnew = newque;msg_ops.associate = msg_security;msg_ops.more_checks = NULL;

msg_params.key = key;msg_params.flg = msgflg;

return ipcget(ns, &msg_ids(ns), &msg_ops, &msg_params);}

newqueue() function allocates new ipc message to ids as invoked via ipcget()

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newque() (ipc/msg.c)

ipc_ids

represent

IPC Resources Type

struct idr ipcs_idr

kern_ipc_prem

represent

IPC Resources

msg_queue

State

Messages

kern_ipc_prem

represent

IPC Resources

msg_queue

State

Messages

msg_queue

Messages

msg_queue

Messages

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• shmget() : Create IPC Share Memory resources or get IPC identifier

• shmat() : Map IPC Share Memory space for user process memory space

• shmdt() : Unmap IPC Share Memory space for user process memory space

Shared Memory

IPC Resource

0

0

Kernel

Data

0

Process1

shmat()shmdt()

Default : 32MBMax : 4096

0

0

Kernel

Data

0

Process2

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• Kernel Implementation (ipc/shm.c)

Shared Memory IPC Resources

SYSCALL_DEFINE3(shmget, key_t, key, size_t, size, int, shmflg){

struct ipc_namespace *ns;struct ipc_ops shm_ops;struct ipc_params shm_params;


shm_ops.getnew = newseg;shm_ops.associate = shm_security;shm_ops.more_checks = shm_more_checks;

shm_params.key = key;shm_params.flg = shmflg;shm_params.u.size = size;

return ipcget(ns, &shm_ids(ns), &shm_ops, &shm_params);}

newseg() function allocates new shared memory to ids as invoked via ipcget()

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newseg() (ipc/shm.c)

ipc_ids

represent

IPC Resources Type

kern_ipc_prem

represent

IPC Resources

shmid_kernel

State

Share Memory

kern_ipc_prem

represent

IPC Resources

shmid_kernel

State

Share Memory

File Object File Object

struct idr ipcs_idr

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• POSIX IPC Mechanism– Same interface as System V IPC

– Implemented in independent pool from System V IPC

– Implemented not through key-identifier design but through file-based design

– Event-driven support (epoll event)

• Unix Domain Socket– General purpose IPC

• Socket supports not only IPC but also diverse network protocols.

– Simple code style, but high overhead compared to other IPC mechanisms.

Other IPCs in Linux

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• Various IPC methods are used in Tizen.– D-Bus

– vconf

– socket

– pipe

• Old Tizen (2.0, 2.1) used socket and pipe for IPC.

• Recent Tizen (2.3~, 3.x) is adopting dbus and vconffor IPC.– Socket D-Bus: system server, AUL, alarm manager,

connectivity manager, BlueZ, NFC manager, …

Tizen Platform IPC

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• Inter-process communication (IPC) mechanism using socket– Simplify the IPC requirements with

single shared channel

– Access control using SMACK

D-Bus

Fig. 1 IPC without D-Bus

Fig. 2 IPC with D-BusFig. 3 D-Bus and SMACK

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• Access control using SMACK (Simplified Mandatory Access Control Kernel)– dbus daemon allow setting the policy to apply using configuration files

explicitly

– Set allow or deny interface/destination

D-Bus Access Control

<busconfig><policy smack="bluez"><allow own="org.bluez"/>

</policy><policy smack="bt_agent::public">

<allow send_destination="org.bluez" send_interface="org.bluez.ProfileManager1" send_member="RegisterProfile1"/>

</policy></busconfig>

[Tizen 2.3]/etc/dubs-1/system.d/manifest.bluez.conf

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• User-level APIs and wrappers to use D-Bus– Low-level API

• DBusConnection

– Connection to another application

• DBusMessage

– Message to be sent or received over a DBusConnection

– D-Bus Wrapper

• EDBus

– D-Bus wrapper for EFL applications

• GDBus

– Glib based D-Bus wrapper

D-Bus in Tizen

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D-Bus Low-level API

Process 1 Process 2

dbus_bus_get () dbus_bus_get ()

dbus_bus_request_name ()

dbus_message_new_method_call()

dbus_message_append_args()

reply=dbus_connection_send_with_reply_and_block()

dbus_message_is_method_call()

dbus_message_get_args()

dbus_message_new_signal()

dbus_message_is_signal()

Init

MethodCall

Signal

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• Used in system framework and UI framework.

• Example: deviced (in system framework)

1. Initialize

• deviced/src/core/edbus-handler.c

EDBus Usage in Tizen

int init_pm_dbus(void){

ret = register_edbus_method(DEVICED_PATH_DISPLAY,

edbus_methods, ARRAY_SIZE(edbus_methods));

void edbus_init(void *data){...

edbus_request_name = e_dbus_request_name(edbus_conn, DEVICED_BUS_NAME,DBUS_NAME_FLAG_REPLACE_EXISTING, request_name_cb, NULL);

...}

static const struct edbus_method edbus_methods[] = {{ "start", NULL, NULL, edbus_start },{ "stop", NULL, NULL, edbus_stop },{ "lockstate", "sssi", "i", edbus_lockstate },{ "unlockstate", "ss", "i", edbus_unlockstate },

2. Register methods (Display device management in deviced)

• deviced/src/display/display-dbus.c

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• Example: deviced (in system framework) (Cont’d)3. Other process send message

• appfw/alarm-manager/alarm-manager.c


static DBusHandlerResult message_filter(DBusConnection *connection, DBusMessage *message, void *data){

ret = dbus_message_get_args(message, NULL, DBUS_TYPE_STRING, &arg,DBUS_TYPE_INVALID);

DD_LIST_FOREACH(edbus_watch_list, n, watch) {if (strcmp(arg, watch->name)) continue;if (watch->func)watch->func(watch->name, watch->id);

}

• Compare method name• Perform function call

int __display_lock_state(char *state, char *flag, unsigned int timeout){

msg = g_dbus_message_new_method_call(DEVICED_BUS_NAME, DEVICED_PATH_DISPLAY, DEVICED_INTERFACE_DISPLAY, DEVICED_LOCK_STATE);

4. Receive and handle the message

• deviced/src/core/edbus-handler.c

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• Example: deviced (in system framework) (Cont’d)5. Perform specific function


static DBusMessage *edbus_lockstate(E_DBus_Object *obj, DBusMessage *msg){

if (!dbus_message_get_args(msg, &err,DBUS_TYPE_STRING, &state_str,DBUS_TYPE_STRING, &option1_str,DBUS_TYPE_STRING, &option2_str,DBUS_TYPE_INT32, &timeout, DBUS_TYPE_INVALID)) {_E("there is no message");ret = -EINVAL;goto out;

}

if (!strcmp(state_str, PM_LCDON_STR))state = LCD_NORMAL;else if (!strcmp(state_str, PM_LCDDIM_STR))state = LCD_DIM;else if (!strcmp(state_str, PM_LCDOFF_STR))state = LCD_OFF;

① Get arguments from message

② Check LCD state

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• Key-value fair + inotify– Store system configuration using SQLite (libsqlfs)

– Able to communicate between inter-process using inotify

• Inotify (inode notify)– Linux kernel subsystem to notify filesystem’s event

• used to notify an event to application

vconf

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vconf

• vconftool– A tool to get or set the configuration values managed by vconf

– Example: Initialize Tizen device configuration values in deviced

• set -t <TYPE> <KEY NAME> <VALUE> <OPTIONS>

• Option

– -i : Install memory backend key into flash space for backup

– -f : Overwrite values by force, even when vconf values are already exist

– -r : retrieve all keys included in sub-directories

– -s : SMACK label

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• Vconf access is controlled by SMACK– Use one of predefined smack labels

– All modules(including applications) will have read permission to those files and only restricted modules have write permission

vconf Access Control

– Label list

• setting : only setting application can write

• inhouse : preloaded applications and platform modules can write

• privacy : only privacy related modules can write

• system : app framework, security, system, base

• multimedia : graphics & UI, multimedia

• network : web, connectivity

• misc : other keys

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• Get the values of Tizen device configuration1. Connect your Tizen Z3 phone

to your PC using micro-USB cable.

2. $ sdb root on

3. $ sdb shell

4. # vconftool get memory/

vconf Usage

…

…

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• Set the values of Tizen device configuration– Notify power-off button event

• # vconftool set -t int memory/sysman/power_off 1 -i -s system::vconf_system -f

– Notify earphone jack event

• # vconftool set -t int memory/sysman/earjack 1 -i -s system::vconf_system -f

– Control battery capacity as 1%

• # vconftool set -t int memory/sysman/battery_capacity 5 -i -s system::vconf_system -f

vconf Usage

Documents

Introduction to Tizen Platform - SKKUnyx.skku.ac.kr/wp-content/uploads/2016/03/Lecture6-Week9.pdf · 2016-05-03 · 36 5 Embedded Software Lab. • The oldest form of UNIX IPC and