전공핵심실습 1: 운영체제론 Chapter 6. Inter-process Communication (IPC)

Transcription

1 1 전공핵심실습 1: 운영체제론 Chapter 6. Inter-process Communication (IPC) Sungkyunkwan University Dongkun Shin

2 Contents 2 Linux Kernel IPC Pipe FIFO System V IPC Semaphore Message Queue Shared Memory Tizen Platform IPC D-Bus vconf

3 Linux Kernel IPC 3 Pipe FIFO System V IPC Semaphore Message Queue Shared Memory

4 IPC System Call 4 User uses IPC mechanism via system calls provided by the kernel Tizen IPC System Calls (# syscall number) PIPE FIFO Semaphore Message Queue Shared Memory PIPE (42) OPEN (5) MSGGET (303) SHMGET (307) SEMGET (299) PIPE2 (359) READ (3) MSGSND (301) SHMAT (305) SEMOP (298) WRITE (4) MSGRCV (302) SHMDT (306) IPC System Call Linux Kernel

5 PIPE 5 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]

6 PIPE (cont.) 6

7 PIPE (cont.) 7 Kernel Implementation (linux/fs/pipe.c) SYSCALL_DEFINE2(pipe2, int user *, fildes, int, flags) { struct file *files[2]; int fd[2]; int error; create 2 pipe files (later in fifo) and open with O_RDONLY and O_WRONLY flags error = do_pipe_flags(fd, files, flags); if (!error) { if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) { fput(files[0]); Copy file descriptors to userspace as an output of the system call 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]); } Install file *s in the file descriptor table of the process } return error; }

8 FIFO (a.k.a named pipe) 8 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)

9 Create Pipe Files 9 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, once.fasync pipefifo_fops = pipe_fasync, is registered as file_operations, }; the normal file I/O functions all work with FIFO

10 FIFO Example 10 In Shell $ cat /proc/meminfo grep I active tail n4 > memory.txt

11 System V IPC 11 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

12 IPC Identifier 12 Key of IPC Resources semget() Get Semaphores IPC Resources msgget() Get Messages IPC Resources shmget() Get Share Memory IPC Resources semget() msgget() + IPC Identifier shmget() (XXX) Process1 IPC resource XXX Process2 Some data for share

13 IPC Resource (include/linux/ipc_namespace.h) 13 ipc_ids represent IPC Resources Type The data structure similar with radix tree to map a id to the corresponding pointer struct idr ipcs_idr kern_ipc_prem represent IPC Resource kern_ipc_prem represent IPC Resource kern_ipc_prem represent IPC Resource

14 Semaphore 14 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 semget() : get IPC Identifier semop() : Decrease or Increase semaphore count semop( struct sembuf ) Process IPC resource Some data for share struct sembuf sem_num : Semaphore number sem_op : Add this to semval (increase / decrease semaphore count) sem_flg : Operation flags

15 Semaphore (ipc/sem.c) 15 Kernel Implementation 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; newary() function allocates new ipc semaphore to ids as invoked via ipcget() 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);

16 newary() (ipc/sem.c) 16 ipc_ids represent IPC Resources Type struct idr ipcs_idr sem_array kern_ipc_prem sem_array kern_ipc_prem represent Semephore represent IPC Resources represent Semephore represent IPC Resources

17 Message Queue 17 IPC Messages msgget() : Create IPC Messages resources or get IPC identifier msgsnd() : Send messages msgrcv() : Receive messages POSIX Message Queue is implemented independently Buffer Data Buffer Data Some data for share msgrcv() msgsnd() Process1 IPC resource XXX Process2

18 Messages IPC Resources 18 Kernel Implementation (ipc/msg.c) SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg) { struct ipc_namespace *ns; struct ipc_ops msg_ops; struct ipc_params msg_params; newqueue() ns = current->nsproxy->ipc_ns; function allocates new message to ids as invoked via ipcget() 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);

19 newque() (ipc/msg.c) 19 ipc_ids represent IPC Resources Type struct idr ipcs_idr msg_queue kern_ipc_prem msg_queue kern_ipc_prem State Messages represent IPC Resources State Messages represent IPC Resources msg_queue msg_queue Messages Messages

20 Shared Memory 20 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 Process1 IPC Resource Process2 0 0 Kernel Data 0 shmat() shmdt() Default : 32MB Max : Kernel Data 0

21 Shared Memory IPC Resources 21 Kernel Implementation (ipc/shm.c) 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; newseg() ns = function current->nsproxy->ipc_ns; allocates new shared memory to ids as invoked via ipcget() 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);

22 newseg() (ipc/shm.c) 22 ipc_ids represent IPC Resources Type struct idr ipcs_idr shmid_kernel kern_ipc_prem shmid_kernel kern_ipc_prem State Share Memory represent IPC Resources State Share Memory represent IPC Resources File Object File Object

23 Other IPCs in Linux 23 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.

24 Tizen Platform IPC 24 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 vconf for IPC. Socket D-Bus: system server, AUL, alarm manager, connectivity manager, BlueZ, NFC manager,

25 D-Bus 25 Inter-process communication (IPC) mechanism using socket Simplify the IPC requirements with single shared channel Access control using SMACK Fig. 1 IPC without D-Bus Fig. 3 D-Bus and SMACK Fig. 2 IPC with D-Bus

26 D-Bus Access Control 26 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 <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

27 D-Bus in Tizen 27 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

28 D-Bus Low-level API 28 Process 1 Process 2 Init dbus_bus_get () dbus_bus_get () dbus_bus_request_name () Method Call dbus_message_new_method_call() dbus_message_append_args() reply=dbus_connection_ send_with_reply_and_block() dbus_message_get_args() dbus_message_is_method_call() Signal dbus_message_new_signal() dbus_message_is_signal()

29 EDBus Usage in Tizen 29 Used in system framework and UI framework. Example: deviced (in system framework) 1. Initialize deviced/src/core/edbus-handler.c 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);... } 2. Register methods (Display device management in deviced) deviced/src/display/display-dbus.c int init_pm_dbus(void) { ret = register_edbus_method(deviced_path_display, edbus_methods, ARRAY_SIZE(edbus_methods)); 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 },

30 EDBus Usage in Tizen 30 Example: deviced (in system framework) (Cont d) 3. Other process send message appfw/alarm-manager/alarm-manager.c 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 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

31 EDBus Usage in Tizen 31 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

32 vconf 32 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

33 vconf 33 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

34 vconf Access Control 34 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 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

35 vconf Usage 35 Get the values of Tizen device configuration 1. Connect your Tizen Z3 phone to your PC using micro-usb cable. 2. $ sdb root on 3. $ sdb shell 4. # vconftool get memory/

36 vconf Usage 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