sem.c File Reference

Classes
struct	sem_info_t
	Semaphore management structure. More...

Macros
#define	__DEBUG_HEADER__   "[IPCsem]"
	Change header.
#define	__DEBUG_LEVEL__   LOGLEVEL_NOTICE
	Set log level.

Functions
static sem_info_t *	__sem_info_alloc (key_t key, int nsems, int semflg)
	Allocates the memory for semaphore management structure. More...
static void	__sem_info_dealloc (sem_info_t *sem_info)
	Frees the memory of a semaphore management structure. More...
static sem_info_t *	__list_find_sem_info_by_id (int semid)
	Searches for the semaphore with the given id. More...
static sem_info_t *	__list_find_sem_info_by_key (key_t key)
	Searches for the semaphore with the given key. More...
static void	__list_add_sem_info (sem_info_t *sem_info)
	Adds the structure to the global list. More...
static void	__list_remove_sem_info (sem_info_t *sem_info)
	Removes the structure from the global list. More...
int	sem_init (void)
	Iinitializes the semaphore system. More...
long	sys_semget (key_t key, int nsems, int semflg)
long	sys_semop (int semid, struct sembuf *sops, unsigned nsops)
long	sys_semctl (int semid, int semnum, int cmd, union semun *arg)
ssize_t	procipc_sem_read (vfs_file_t *file, char *buf, off_t offset, size_t nbyte)
	Read function for the proc system. More...

Variables
int	__sem_id = 0
	A value to compute the semid value.
list_head	semaphores_list
	List of all current active semaphores.

Detailed Description

Copyright

(c) 2014-2024 This file is distributed under the MIT License. See LICENSE.md for details.

03/04/2023

At the moment we have various functions with their description (see comments). The first time that the function semget is called, we are going to generate the list and the first semaphore set with the assumption that we are not given a IPC_PRIVATE key (temporary ofc). We are able to create new semaphores set and generate unique keys (IPC_PRIVATE) with a counter that searches for the first possible key to assign. Temporary idea:

• IPC_CREAT flag, it should be working properly, it creates a semaphore set with the given key.
• IPC_EXCL flag, it should be working properly, it returns -1 and sets the errno if the key is already used.

11/04/2023

Right now we have a first version of working semaphores in MentOS. We have completed the semctl function and we have implemented the first version of the semop function both user and kernel side. The way it works is pretty straightforward, the user tries to perform an operation and based on the value of the semaphore the kernel returns certain values. If the operation cannot be performed then the user will stay in a while loop. The cycle ends with a positive return value (the operation has been taken care of) or in case of errors. For testing purposes -> you can try the t_semget and the t_sem1 tests. They both use semaphores and blocking / non blocking operations. t_sem1 is also an exercise that was assingned by Professor Drago in the OS course.

Function Documentation

__list_add_sem_info()

static void __list_add_sem_info ( sem_info_t *  sem_info )

inlinestatic

Adds the structure to the global list.

Parameters

sem_info

the structure to add.

__list_find_sem_info_by_id()

static sem_info_t* __list_find_sem_info_by_id ( int  semid )

inlinestatic

Searches for the semaphore with the given id.

Parameters

semid

the id we are searching.

Returns

the semaphore with the given id.

__list_find_sem_info_by_key()

static sem_info_t* __list_find_sem_info_by_key ( key_t  key )

inlinestatic

Searches for the semaphore with the given key.

Parameters

key	the key we are searching.

Returns

the semaphore with the given key.

__list_remove_sem_info()

static void __list_remove_sem_info ( sem_info_t *  sem_info )

inlinestatic

Removes the structure from the global list.

Parameters

sem_info

the structure to remove.

__sem_info_alloc()

static sem_info_t* __sem_info_alloc ( key_t  key, int  nsems, int  semflg  )

inlinestatic

Allocates the memory for semaphore management structure.

Parameters

key	IPC_KEY associated with the set of semaphores.
nsems	number of semaphores to initialize.
semflg	flags used to create the set of semaphores.

Returns

a pointer to the allocated semaphore management structure.

__sem_info_dealloc()

static void __sem_info_dealloc ( sem_info_t *  sem_info )

inlinestatic

Frees the memory of a semaphore management structure.

Parameters

sem_info

pointer to the semaphore management structure.

procipc_sem_read()

ssize_t procipc_sem_read	(	vfs_file_t *	file,
		char *	buf,
		off_t	offset,
		size_t	nbyte
	)

Read function for the proc system.

Parameters

file	The file.
buf	Buffer where the read content must be placed.
offset	Offset from which we start reading from the file.
nbyte	The number of bytes to read.

Returns

The number of red bytes.

sem_init()

int sem_init

(

void

)

Iinitializes the semaphore system.

Returns

0 on success, 1 on failure.