include/linux/shm.h

#ifndef _LINUX_SHM_H_
#define _LINUX_SHM_H_
#include <linux/ipc.h>

struct shmid_ds {
	struct	ipc_perm shm_perm;	/* operation perms */
	int	shm_segsz;		/* size of segment (bytes) */
	time_t	shm_atime;		/* last attach time */
	time_t	shm_dtime;		/* last detach time */
	time_t	shm_ctime;		/* last change time */
	unsigned short	shm_cpid;	/* pid of creator */
	unsigned short	shm_lpid;	/* pid of last operator */
	short	shm_nattch;		/* no. of current attaches */
	/* the following are private */
	unsigned short   shm_npages;  /* size of segment (pages) */
	unsigned long   *shm_pages;   /* array of ptrs to frames -> SHMMAX */ 
	struct shm_desc *attaches;    /* descriptors for attaches */
};

/* mode for attach */
#define	SHM_RDONLY	010000	/* read-only access */
#define	SHM_RND		020000	/* round attach address to SHMLBA boundary */
#define	SHM_REMAP	040000	/* take-over region on attach */

/* super user shmctl commands */
#define SHM_LOCK 	11
#define SHM_UNLOCK 	12

struct	shminfo {
    int shmmax;	
    int shmmin;	
    int shmmni;	
    int shmseg;	
    int shmall;	
};

#define SHM_RANGE_START	0x40000000
#define SHM_RANGE_END	0x60000000

				/* _SHM_ID_BITS is a variable you can adjust to */
				/* tune the kernel.  It determines the value of */
				/* SHMMNI, which specifies the maximum no. of */
				/* shared segments (system wide).  SRB. */
#define _SHM_ID_BITS	7		/* keep as low as possible */
					/* a static array is declared */
					/* using SHMMNI */

#define __SHM_IDX_BITS	(BITS_PER_PTR-2-SHM_IDX_SHIFT)

/* !!!!!!!?????
 * Why reserve the two (2) high bits of the signature (shm_sgn) field?
 * Since, as far as I can see, only the high bit is used (SHM_READ_ONLY).
 *						SRB.
 */

#define _SHM_IDX_BITS	(__SHM_IDX_BITS+PAGE_SHIFT>=BITS_PER_PTR?\
 BITS_PER_PTR-PAGE_SHIFT-1:__SHM_IDX_BITS)	/* sanity check */

/* not present page table entry format bit 0 is 0, low byte defined in mm.h */
#define SHM_ID_SHIFT	8
#define SHM_ID_MASK	((1<<_SHM_ID_BITS)-1)
#define SHM_IDX_SHIFT	(SHM_ID_SHIFT+_SHM_ID_BITS)
#define SHM_IDX_MASK	((1<<_SHM_IDX_BITS)-1)
#define SHM_READ_ONLY	(1<<(BITS_PER_PTR-1))

#define SHMMAX 0x3fa000				/* max shared seg size (bytes) */
#define SHMMIN 1	 /* really PAGE_SIZE */	/* min shared seg size (bytes) */
#define SHMMNI (1<<_SHM_ID_BITS)		/* max num of segs system wide */
#define SHMALL (1<<(_SHM_IDX_BITS+_SHM_ID_BITS))/* max shm system wide (pages) */
#define	SHMLBA 0x1000				/* attach addr a multiple of this */
#define SHMSEG SHMMNI				/* max shared segs per process */

#ifdef __KERNEL__

/* shm_mode upper byte flags */
#define	SHM_DEST	01000	/* segment will be destroyed on last detach */
#define SHM_LOCKED      02000   /* segment will not be swapped */

/* ipcs ctl commands */
#define SHM_STAT 	13
#define SHM_INFO 	14
struct shm_info {
	int   used_ids;
	ulong shm_tot; /* total allocated shm */
	ulong shm_rss; /* total resident shm */
	ulong shm_swp; /* total swapped shm */
	ulong swap_attempts;
	ulong swap_successes;
};


/*
 * Per process internal structure for managing segments.
 * A shmat will add to and shmdt will remove from the list.
 */
struct	shm_desc {
	struct task_struct *task;     /* attacher */
	unsigned long shm_sgn;        /* signature for this attach */
	unsigned long start;   /* virt addr of attach, multiple of SHMLBA */
	unsigned long end;            /* multiple of SHMLBA */
	struct shm_desc *task_next;   /* next attach for task */
	struct shm_desc *seg_next;    /* next attach for segment */
};

#endif /* __KERNEL__ */

#endif /* _LINUX_SHM_H_ */