shm.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * shm.c
 *	  System V Shared Memory Emulation
 *
 * Copyright (c) 1999, repas AEG Automation GmbH
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/port/qnx4/shm.c,v 1.8 2002/11/08 20:23:56 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include <sys/stat.h>


#define MODE	0777

#define SHMMAX	1024


struct shm_info
{
	int			shmid;
	key_t		key;
	size_t		size;
	void	   *addr;
};

static struct shm_info *ShmInfo;


static int	shm_putinfo(struct shm_info * info);
static int	shm_updinfo(int i, struct shm_info * info);
static int	shm_getinfo(int shmid, struct shm_info * info);
static int	shm_getinfobyaddr(const void *addr, struct shm_info * info);

static char *
keytoname(key_t key, char *name)
{
	sprintf(name, "PgShm%x", key);
	return name;
}

static int
shm_putinfo(struct shm_info * info)
{
	int			i;

	if (ShmInfo == NULL)
	{
		ShmInfo = calloc(SHMMAX, sizeof(struct shm_info));
		if (ShmInfo == NULL)
			return -1;
		/* initialize ShmInfo */
		for (i = 0; i < SHMMAX; i++)
			ShmInfo[i].shmid = -1;
	}

	/* search first free element */
	i = 0;
	while (i < SHMMAX && ShmInfo[i].shmid != -1)
		i++;
	if (i >= SHMMAX)
	{
		errno = ENOSPC;
		return -1;
	}

	memcpy(&ShmInfo[i], info, sizeof(struct shm_info));

	return i;
}

static int
shm_updinfo(int i, struct shm_info * info)
{
	if (i >= SHMMAX)
		return -1;
	if (ShmInfo == NULL)
		return -1;

	memcpy(&ShmInfo[i], info, sizeof(struct shm_info));

	return i;
}

static int
shm_getinfo(int shmid, struct shm_info * info)
{
	int			i;

	if (ShmInfo == NULL)
		return -1;

	/* search element */
	i = 0;
	while (i < SHMMAX && ShmInfo[i].shmid != shmid)
		i++;
	if (i >= SHMMAX)
		return -1;

	memcpy(info, &ShmInfo[i], sizeof(struct shm_info));

	return i;
}

static int
shm_getinfobyaddr(const void *addr, struct shm_info * info)
{
	int			i;

	if (ShmInfo == (struct shm_info *) - 1)
		return -1;

	/* search element */
	i = 0;
	while (i < SHMMAX && ShmInfo[i].addr != addr)
		i++;
	if (i >= SHMMAX)
		return -1;

	memcpy(info, &ShmInfo[i], sizeof(struct shm_info));

	return i;
}


void *
shmat(int shmid, const void *shmaddr, int shmflg)
{
	struct shm_info info;
	int			i;

	i = shm_getinfo(shmid, &info);
	if (i == -1)
	{
		errno = EACCES;
		return (void *) -1;
	}

	info.addr = mmap((void *) shmaddr, info.size,
					 PROT_READ | PROT_WRITE, MAP_SHARED, shmid, 0);
	if (info.addr == MAP_FAILED)
		return info.addr;

	if (shm_updinfo(i, &info) == -1)
	{
		errno = EACCES;
		return (void *) -1;
	}

	return info.addr;
}

int
shmdt(const void *addr)
{
	struct shm_info info;

	if (shm_getinfobyaddr(addr, &info) == -1)
	{
		errno = EACCES;
		return -1;
	}

	return munmap((void *) addr, info.size);
}

int
shmctl(int shmid, int cmd, struct shmid_ds * buf)
{
	struct shm_info info;
	char		name[NAME_MAX + 1];
	int			result;
	int			fd;
	struct stat statbuf;


	switch (cmd)
	{
		case IPC_RMID:
			if (shm_getinfo(shmid, &info) == -1)
			{
				errno = EACCES;
				return -1;
			}
			close(info.shmid);
			keytoname(info.key, name);
			return shm_unlink(name);

		case IPC_STAT:

			/*
			 * we have to open it first. stat() does no prefix tracking ->
			 * the call would go to fsys instead of proc
			 */
			keytoname(shmid, name);
			fd = shm_open(name, 0, MODE);
			if (fd >= 0)
			{
				result = fstat(fd, &statbuf);

				/*
				 * if the file exists, subtract 2 from linkcount : one for
				 * our own open and one for the dir entry
				 */
				if (!result)
					buf->shm_nattch = statbuf.st_nlink - 2;
				close(fd);
				return result;
			}
			else
			{
				/*
				 * if there's no entry for this key it doesn't matter the
				 * next shmget() would get a different shm anyway
				 */
				buf->shm_nattch = 0;
				return 0;
			}
	}
	errno = EINVAL;
	return -1;
}

int
shmget(key_t key, size_t size, int flags)
{
	char		name[NAME_MAX + 1];
	int			oflag = 0;
	struct shm_info info;

	if (flags & IPC_CREAT)
		oflag |= O_CREAT;
	if (flags & IPC_EXCL)
		oflag |= O_EXCL;
	if (flags & SHM_R)
	{
		if (flags & SHM_W)
			oflag |= O_RDWR;
		else
			oflag |= O_RDONLY;
	}
	info.shmid = shm_open(keytoname(key, name), oflag, MODE);

	/* store shared memory information */
	if (info.shmid != -1)
	{
		info.key = key;
		info.size = size;
		info.addr = NULL;
		if (shm_putinfo(&info) == -1)
		{
			close(info.shmid);
			if ((oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))
				shm_unlink(name);
			return -1;
		}
	}

	/* The size may only be set once. Ignore errors. */
	ltrunc(info.shmid, size, SEEK_SET);

	return info.shmid;
}