/*
 * linux/ipc/shm.c
 * Copyright (C) 1992, 1993 Krishna Balasubramanian
 *         Many improvements/fixes by Bruno Haible.
 * Replaced `struct shm_desc' by `struct vm_area_struct', July 1994.
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/ipc.h>
#include <linux/shm.h>
#include <linux/stat.h>
#include <linux/malloc.h>
#include <linux/swap.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/init.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>

extern int ipcperms (struct ipc_perm *ipcp, short shmflg);
extern unsigned long get_swap_page (void);
static int findkey (key_t key);
static int newseg (key_t key, int shmflg, int size);
static int shm_map (struct vm_area_struct *shmd);
static void killseg (int id);
static void shm_open (struct vm_area_struct *shmd);
static void shm_close (struct vm_area_struct *shmd);
static pte_t shm_swap_in(struct vm_area_struct *, unsigned long, unsigned long);

static int shm_tot = 0; /* total number of shared memory pages */
static int shm_rss = 0; /* number of shared memory pages that are in memory */
static int shm_swp = 0; /* number of shared memory pages that are in swap */
static int max_shmid = 0; /* every used id is <= max_shmid */
static struct wait_queue *shm_lock = NULL; /* calling findkey() may need to wait */
static struct shmid_ds *shm_segs[SHMMNI];

static unsigned short shm_seq = 0; /* incremented, for recognizing stale ids */

/* some statistics */
static ulong swap_attempts = 0;
static ulong swap_successes = 0;
static ulong used_segs = 0;

__initfunc(void shm_init (void))
{
        int id;

        for (id = 0; id < SHMMNI; id++)
                shm_segs[id] = (struct shmid_ds *) IPC_UNUSED;
        shm_tot = shm_rss = shm_seq = max_shmid = used_segs = 0;
        shm_lock = NULL;
        return;
}

static int findkey (key_t key)
{
        int id;
        struct shmid_ds *shp;

        for (id = 0; id <= max_shmid; id++) {
                while ((shp = shm_segs[id]) == IPC_NOID)
                        sleep_on (&shm_lock);
                if (shp == IPC_UNUSED)
                        continue;
                if (key == shp->shm_perm.key)
                        return id;
        }
        return -1;
}

/*
 * allocate new shmid_ds and pgtable. protected by shm_segs[id] = NOID.
 */
static int newseg (key_t key, int shmflg, int size)
{
        struct shmid_ds *shp;
        int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
        int id, i;

        if (size < SHMMIN)
                return -EINVAL;
        if (shm_tot + numpages >= SHMALL)
                return -ENOSPC;
        for (id = 0; id < SHMMNI; id++)
                if (shm_segs[id] == IPC_UNUSED) {
                        shm_segs[id] = (struct shmid_ds *) IPC_NOID;
                        goto found;
                }
        return -ENOSPC;

found:
        shp = (struct shmid_ds *) kmalloc (sizeof (*shp), GFP_KERNEL);
        if (!shp) {
                shm_segs[id] = (struct shmid_ds *) IPC_UNUSED;
                wake_up (&shm_lock);
                return -ENOMEM;
        }

        shp->shm_pages = (ulong *) kmalloc (numpages*sizeof(ulong),GFP_KERNEL);
        if (!shp->shm_pages) {
                shm_segs[id] = (struct shmid_ds *) IPC_UNUSED;
                wake_up (&shm_lock);
                kfree(shp);
                return -ENOMEM;
        }

        for (i = 0; i < numpages; shp->shm_pages[i++] = 0);
        shm_tot += numpages;
        shp->shm_perm.key = key;
        shp->shm_perm.mode = (shmflg & S_IRWXUGO);
        shp->shm_perm.cuid = shp->shm_perm.uid = current->euid;
        shp->shm_perm.cgid = shp->shm_perm.gid = current->egid;
        shp->shm_perm.seq = shm_seq;
        shp->shm_segsz = size;
        shp->shm_cpid = current->pid;
        shp->attaches = NULL;
        shp->shm_lpid = shp->shm_nattch = 0;
        shp->shm_atime = shp->shm_dtime = 0;
        shp->shm_ctime = CURRENT_TIME;
        shp->shm_npages = numpages;

        if (id > max_shmid)
                max_shmid = id;
        shm_segs[id] = shp;
        used_segs++;
        wake_up (&shm_lock);
        return (unsigned int) shp->shm_perm.seq * SHMMNI + id;
}

asmlinkage int sys_shmget (key_t key, int size, int shmflg)
{
        struct shmid_ds *shp;
        int err, id = 0;

        lock_kernel();
        if (size < 0 || size > SHMMAX) {
                err = -EINVAL;
        } else if (key == IPC_PRIVATE) {
                err = newseg(key, shmflg, size);
        } else if ((id = findkey (key)) == -1) {
                if (!(shmflg & IPC_CREAT))
                        err = -ENOENT;
                else
                        err = newseg(key, shmflg, size);
        } else if ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) {
                err = -EEXIST;
        } else {
                shp = shm_segs[id];
                if (shp->shm_perm.mode & SHM_DEST)
                        err = -EIDRM;
                else if (size > shp->shm_segsz)
                        err = -EINVAL;
                else if (ipcperms (&shp->shm_perm, shmflg))
                        err = -EACCES;
                else
                        err = (int) shp->shm_perm.seq * SHMMNI + id;
        }
        unlock_kernel();
        return err;
}

/*
 * Only called after testing nattch and SHM_DEST.
 * Here pages, pgtable and shmid_ds are freed.
 */
static void killseg (int id)
{
        struct shmid_ds *shp;
        int i, numpages;

        shp = shm_segs[id];
        if (shp == IPC_NOID || shp == IPC_UNUSED) {
                printk ("shm nono: killseg called on unused seg id=%d\n", id);
                return;
        }
        shp->shm_perm.seq++;     /* for shmat */
        shm_seq = (shm_seq+1) % ((unsigned)(1<<31)/SHMMNI); /* increment, but avoid overflow */
        shm_segs[id] = (struct shmid_ds *) IPC_UNUSED;
        used_segs--;
        if (id == max_shmid)
                while (max_shmid && (shm_segs[--max_shmid] == IPC_UNUSED));
        if (!shp->shm_pages) {
                printk ("shm nono: killseg shp->pages=NULL. id=%d\n", id);
                return;
        }
        numpages = shp->shm_npages;
        for (i = 0; i < numpages ; i++) {
                pte_t pte;
                pte = __pte(shp->shm_pages[i]);
                if (pte_none(pte))
                        continue;
                if (pte_present(pte)) {
                        free_page (pte_page(pte));
                        shm_rss--;
                } else {
                        swap_free(pte_val(pte));
                        shm_swp--;
                }
        }
        kfree(shp->shm_pages);
        shm_tot -= numpages;
        kfree(shp);
        return;
}

asmlinkage int sys_shmctl (int shmid, int cmd, struct shmid_ds *buf)
{
        struct shmid_ds tbuf;
        struct shmid_ds *shp;
        struct ipc_perm *ipcp;
        int id, err = -EINVAL;

        lock_kernel();
        if (cmd < 0 || shmid < 0)
                goto out;
        if (cmd == IPC_SET) {
                err = -EFAULT;
                if (!buf)
                        goto out;
                err = verify_area (VERIFY_READ, buf, sizeof (*buf));
                if (err)
                        goto out;
                copy_from_user (&tbuf, buf, sizeof (*buf));
        }

        switch (cmd) { /* replace with proc interface ? */
        case IPC_INFO:
        {
                struct shminfo shminfo;
                err = -EFAULT;
                if (!buf)
                        goto out;
                shminfo.shmmni = SHMMNI;
                shminfo.shmmax = SHMMAX;
                shminfo.shmmin = SHMMIN;
                shminfo.shmall = SHMALL;
                shminfo.shmseg = SHMSEG;
                err = verify_area (VERIFY_WRITE, buf, sizeof (struct shminfo));
                if (err)
                        goto out;
                copy_to_user (buf, &shminfo, sizeof(struct shminfo));
                err = max_shmid;
                goto out;
        }
        case SHM_INFO:
        {
                struct shm_info shm_info;
                err = -EFAULT;
                if (!buf)
                        goto out;
                err = verify_area (VERIFY_WRITE, buf, sizeof (shm_info));
                if (err)
                        goto out;
                shm_info.used_ids = used_segs;
                shm_info.shm_rss = shm_rss;
                shm_info.shm_tot = shm_tot;
                shm_info.shm_swp = shm_swp;
                shm_info.swap_attempts = swap_attempts;
                shm_info.swap_successes = swap_successes;
                copy_to_user (buf, &shm_info, sizeof(shm_info));
                err = max_shmid;
                goto out;
        }
        case SHM_STAT:
                err = -EFAULT;
                if (!buf)
                        goto out;
                err = verify_area (VERIFY_WRITE, buf, sizeof (*buf));
                if (err)
                        goto out;
                err = -EINVAL;
                if (shmid > max_shmid)
                        goto out;
                shp = shm_segs[shmid];
                if (shp == IPC_UNUSED || shp == IPC_NOID)
                        goto out;
                if (ipcperms (&shp->shm_perm, S_IRUGO))
                        goto out;
                id = (unsigned int) shp->shm_perm.seq * SHMMNI + shmid;
                tbuf.shm_perm   = shp->shm_perm;
                tbuf.shm_segsz  = shp->shm_segsz;
                tbuf.shm_atime  = shp->shm_atime;
                tbuf.shm_dtime  = shp->shm_dtime;
                tbuf.shm_ctime  = shp->shm_ctime;
                tbuf.shm_cpid   = shp->shm_cpid;
                tbuf.shm_lpid   = shp->shm_lpid;
                tbuf.shm_nattch = shp->shm_nattch;
                copy_to_user (buf, &tbuf, sizeof(*buf));
                err = id;
                goto out;
        }

        shp = shm_segs[id = (unsigned int) shmid % SHMMNI];
        err = -EINVAL;
        if (shp == IPC_UNUSED || shp == IPC_NOID)
                goto out;
        err = -EIDRM;
        if (shp->shm_perm.seq != (unsigned int) shmid / SHMMNI)
                goto out;
        ipcp = &shp->shm_perm;

        switch (cmd) {
        case SHM_UNLOCK:
                err = -EPERM;
                if (!suser())
                        goto out;
                err = -EINVAL;
                if (!(ipcp->mode & SHM_LOCKED))
                        goto out;
                ipcp->mode &= ~SHM_LOCKED;
                break;
        case SHM_LOCK:
/* Allow superuser to lock segment in memory */
/* Should the pages be faulted in here or leave it to user? */
/* need to determine interaction with current->swappable */
                err = -EPERM;
                if (!suser())
                        goto out;
                err = -EINVAL;
                if (ipcp->mode & SHM_LOCKED)
                        goto out;
                ipcp->mode |= SHM_LOCKED;
                break;
        case IPC_STAT:
                err = -EACCES;
                if (ipcperms (ipcp, S_IRUGO))
                        goto out;
                err = -EFAULT;
                if (!buf)
                        goto out;
                err = verify_area (VERIFY_WRITE, buf, sizeof (*buf));
                if (err)
                        goto out;
                tbuf.shm_perm   = shp->shm_perm;
                tbuf.shm_segsz  = shp->shm_segsz;
                tbuf.shm_atime  = shp->shm_atime;
                tbuf.shm_dtime  = shp->shm_dtime;
                tbuf.shm_ctime  = shp->shm_ctime;
                tbuf.shm_cpid   = shp->shm_cpid;
                tbuf.shm_lpid   = shp->shm_lpid;
                tbuf.shm_nattch = shp->shm_nattch;
                copy_to_user (buf, &tbuf, sizeof(*buf));
                break;
        case IPC_SET:
                if (suser() || current->euid == shp->shm_perm.uid ||
                    current->euid == shp->shm_perm.cuid) {
                        ipcp->uid = tbuf.shm_perm.uid;
                        ipcp->gid = tbuf.shm_perm.gid;
                        ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
                                | (tbuf.shm_perm.mode & S_IRWXUGO);
                        shp->shm_ctime = CURRENT_TIME;
                        break;
                }
                err = -EPERM;
                goto out;
        case IPC_RMID:
                if (suser() || current->euid == shp->shm_perm.uid ||
                    current->euid == shp->shm_perm.cuid) {
                        shp->shm_perm.mode |= SHM_DEST;
                        if (shp->shm_nattch <= 0)
                                killseg (id);
                        break;
                }
                err = -EPERM;
                goto out;
        default:
                err = -EINVAL;
                goto out;
        }
        err = 0;
out:
        unlock_kernel();
        return err;
}

/*
 * The per process internal structure for managing segments is
 * `struct vm_area_struct'.
 * A shmat will add to and shmdt will remove from the list.
 * shmd->vm_mm          the attacher
 * shmd->vm_start       virt addr of attach, multiple of SHMLBA
 * shmd->vm_end         multiple of SHMLBA
 * shmd->vm_next        next attach for task
 * shmd->vm_next_share  next attach for segment
 * shmd->vm_offset      offset into segment
 * shmd->vm_pte         signature for this attach
 */

static struct vm_operations_struct shm_vm_ops = {
        shm_open,               /* open - callback for a new vm-area open */
        shm_close,              /* close - callback for when the vm-area is released */
        NULL,                   /* no need to sync pages at unmap */
        NULL,                   /* protect */
        NULL,                   /* sync */
        NULL,                   /* advise */
        NULL,                   /* nopage (done with swapin) */
        NULL,                   /* wppage */
        NULL,                   /* swapout (hardcoded right now) */
        shm_swap_in             /* swapin */
};

/* Insert shmd into the list shp->attaches */
static inline void insert_attach (struct shmid_ds * shp, struct vm_area_struct * shmd)
{
        if((shmd->vm_next_share = shp->attaches) != NULL)
                shp->attaches->vm_pprev_share = &shmd->vm_next_share;
        shp->attaches = shmd;
        shmd->vm_pprev_share = &shp->attaches;
}

/* Remove shmd from list shp->attaches */
static inline void remove_attach (struct shmid_ds * shp, struct vm_area_struct * shmd)
{
        if(shmd->vm_next_share)
                shmd->vm_next_share->vm_pprev_share = shmd->vm_pprev_share;
        *shmd->vm_pprev_share = shmd->vm_next_share;
}

/*
 * ensure page tables exist
 * mark page table entries with shm_sgn.
 */
static int shm_map (struct vm_area_struct *shmd)
{
        pgd_t *page_dir;
        pmd_t *page_middle;
        pte_t *page_table;
        unsigned long tmp, shm_sgn;
        int error;

        /* clear old mappings */
        do_munmap(shmd->vm_start, shmd->vm_end - shmd->vm_start);

        /* add new mapping */
        tmp = shmd->vm_end - shmd->vm_start;
        if((current->mm->total_vm << PAGE_SHIFT) + tmp
           > (unsigned long) current->rlim[RLIMIT_AS].rlim_cur)
                return -ENOMEM;
        current->mm->total_vm += tmp >> PAGE_SHIFT;
        insert_vm_struct(current->mm, shmd);
        merge_segments(current->mm, shmd->vm_start, shmd->vm_end);

        /* map page range */
        error = 0;
        shm_sgn = shmd->vm_pte +
          SWP_ENTRY(0, (shmd->vm_offset >> PAGE_SHIFT) << SHM_IDX_SHIFT);
        flush_cache_range(shmd->vm_mm, shmd->vm_start, shmd->vm_end);
        for (tmp = shmd->vm_start;
             tmp < shmd->vm_end;
             tmp += PAGE_SIZE, shm_sgn += SWP_ENTRY(0, 1 << SHM_IDX_SHIFT))
        {
                page_dir = pgd_offset(shmd->vm_mm,tmp);
                page_middle = pmd_alloc(page_dir,tmp);
                if (!page_middle) {
                        error = -ENOMEM;
                        break;
                }
                page_table = pte_alloc(page_middle,tmp);
                if (!page_table) {
                        error = -ENOMEM;
                        break;
                }
                set_pte(page_table, __pte(shm_sgn));
        }
        flush_tlb_range(shmd->vm_mm, shmd->vm_start, shmd->vm_end);
        return error;
}

/*
 * Fix shmaddr, allocate descriptor, map shm, add attach descriptor to lists.
 */
asmlinkage int sys_shmat (int shmid, char *shmaddr, int shmflg, ulong *raddr)
{
        struct shmid_ds *shp;
        struct vm_area_struct *shmd;
        int err = -EINVAL;
        unsigned int id;
        unsigned long addr;
        unsigned long len;

        lock_kernel();
        if (shmid < 0) {
                /* printk("shmat() -> EINVAL because shmid = %d < 0\n",shmid); */
                goto out;
        }

        shp = shm_segs[id = (unsigned int) shmid % SHMMNI];
        if (shp == IPC_UNUSED || shp == IPC_NOID) {
                /* printk("shmat() -> EINVAL because shmid = %d is invalid\n",shmid); */
                goto out;
        }

        if (!(addr = (ulong) shmaddr)) {
                if (shmflg & SHM_REMAP)
                        goto out;
                err = -ENOMEM;
                addr = 0;
        again:
                if (!(addr = get_unmapped_area(addr, shp->shm_segsz)))
                        goto out;
                if(addr & (SHMLBA - 1)) {
                        addr = (addr + (SHMLBA - 1)) & ~(SHMLBA - 1);
                        goto again;
                }
        } else if (addr & (SHMLBA-1)) {
                if (shmflg & SHM_RND)
                        addr &= ~(SHMLBA-1);       /* round down */
                else
                        goto out;
        }
        /*
         * Check if addr exceeds TASK_SIZE (from do_mmap)
         */
        len = PAGE_SIZE*shp->shm_npages;
        err = -EINVAL;
        if (addr >= TASK_SIZE || len > TASK_SIZE  || addr > TASK_SIZE - len)
                goto out;
        /*
         * If shm segment goes below stack, make sure there is some
         * space left for the stack to grow (presently 4 pages).
         */
        if (addr < current->mm->start_stack &&
            addr > current->mm->start_stack - PAGE_SIZE*(shp->shm_npages + 4))
        {
                /* printk("shmat() -> EINVAL because segment intersects stack\n"); */
                goto out;
        }
        if (!(shmflg & SHM_REMAP))
                if ((shmd = find_vma_intersection(current->mm, addr, addr + shp->shm_segsz))) {
                        /* printk("shmat() -> EINVAL because the interval [0x%lx,0x%lx) intersects an already mapped interval [0x%lx,0x%lx).\n",
                                addr, addr + shp->shm_segsz, shmd->vm_start, shmd->vm_end); */
                        goto out;
                }

        err = -EACCES;
        if (ipcperms(&shp->shm_perm, shmflg & SHM_RDONLY ? S_IRUGO : S_IRUGO|S_IWUGO))
                goto out;
        err = -EIDRM;
        if (shp->shm_perm.seq != (unsigned int) shmid / SHMMNI)
                goto out;

        err = -ENOMEM;
        shmd = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!shmd)
                goto out;
        if ((shp != shm_segs[id]) || (shp->shm_perm.seq != (unsigned int) shmid / SHMMNI)) {
                kmem_cache_free(vm_area_cachep, shmd);
                err = -EIDRM;
                goto out;
        }

        shmd->vm_pte = SWP_ENTRY(SHM_SWP_TYPE, id);
        shmd->vm_start = addr;
        shmd->vm_end = addr + shp->shm_npages * PAGE_SIZE;
        shmd->vm_mm = current->mm;
        shmd->vm_page_prot = (shmflg & SHM_RDONLY) ? PAGE_READONLY : PAGE_SHARED;
        shmd->vm_flags = VM_SHM | VM_MAYSHARE | VM_SHARED
                         | VM_MAYREAD | VM_MAYEXEC | VM_READ | VM_EXEC
                         | ((shmflg & SHM_RDONLY) ? 0 : VM_MAYWRITE | VM_WRITE);
        shmd->vm_dentry = NULL;
        shmd->vm_offset = 0;
        shmd->vm_ops = &shm_vm_ops;

        shp->shm_nattch++;            /* prevent destruction */
        if ((err = shm_map (shmd))) {
                if (--shp->shm_nattch <= 0 && shp->shm_perm.mode & SHM_DEST)
                        killseg(id);
                kmem_cache_free(vm_area_cachep, shmd);
                goto out;
        }

        insert_attach(shp,shmd);  /* insert shmd into shp->attaches */

        shp->shm_lpid = current->pid;
        shp->shm_atime = CURRENT_TIME;

        *raddr = addr;
        err = 0;
out:
        unlock_kernel();
        return err;
}

/* This is called by fork, once for every shm attach. */
static void shm_open (struct vm_area_struct *shmd)
{
        unsigned int id;
        struct shmid_ds *shp;

        id = SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK;
        shp = shm_segs[id];
        if (shp == IPC_UNUSED) {
                printk("shm_open: unused id=%d PANIC\n", id);
                return;
        }
        insert_attach(shp,shmd);  /* insert shmd into shp->attaches */
        shp->shm_nattch++;
        shp->shm_atime = CURRENT_TIME;
        shp->shm_lpid = current->pid;
}

/*
 * remove the attach descriptor shmd.
 * free memory for segment if it is marked destroyed.
 * The descriptor has already been removed from the current->mm->mmap list
 * and will later be kfree()d.
 */
static void shm_close (struct vm_area_struct *shmd)
{
        struct shmid_ds *shp;
        int id;

        /* remove from the list of attaches of the shm segment */
        id = SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK;
        shp = shm_segs[id];
        remove_attach(shp,shmd);  /* remove from shp->attaches */
        shp->shm_lpid = current->pid;
        shp->shm_dtime = CURRENT_TIME;
        if (--shp->shm_nattch <= 0 && shp->shm_perm.mode & SHM_DEST)
                killseg (id);
}

/*
 * detach and kill segment if marked destroyed.
 * The work is done in shm_close.
 */
asmlinkage int sys_shmdt (char *shmaddr)
{
        struct vm_area_struct *shmd, *shmdnext;

        for (shmd = current->mm->mmap; shmd; shmd = shmdnext) {
                shmdnext = shmd->vm_next;
                if (shmd->vm_ops == &shm_vm_ops
                    && shmd->vm_start - shmd->vm_offset == (ulong) shmaddr)
                        do_munmap(shmd->vm_start, shmd->vm_end - shmd->vm_start);
        }
        return 0;
}

/*
 * page not present ... go through shm_pages
 */
static pte_t shm_swap_in(struct vm_area_struct * shmd, unsigned long offset, unsigned long code)
{
        pte_t pte;
        struct shmid_ds *shp;
        unsigned int id, idx;

        id = SWP_OFFSET(code) & SHM_ID_MASK;
        if (id != (SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK)) {
                printk ("shm_swap_in: code id = %d and shmd id = %ld differ\n",
                        id, SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK);
                return BAD_PAGE;
        }
        if (id > max_shmid) {
                printk ("shm_swap_in: id=%d too big. proc mem corrupted\n", id);
                return BAD_PAGE;
        }
        shp = shm_segs[id];
        if (shp == IPC_UNUSED || shp == IPC_NOID) {
                printk ("shm_swap_in: id=%d invalid. Race.\n", id);
                return BAD_PAGE;
        }
        idx = (SWP_OFFSET(code) >> SHM_IDX_SHIFT) & SHM_IDX_MASK;
        if (idx != (offset >> PAGE_SHIFT)) {
                printk ("shm_swap_in: code idx = %u and shmd idx = %lu differ\n",
                        idx, offset >> PAGE_SHIFT);
                return BAD_PAGE;
        }
        if (idx >= shp->shm_npages) {
                printk ("shm_swap_in : too large page index. id=%d\n", id);
                return BAD_PAGE;
        }

        pte = __pte(shp->shm_pages[idx]);
        if (!pte_present(pte)) {
                unsigned long page = get_free_page(GFP_KERNEL);
                if (!page) {
                        oom(current);
                        return BAD_PAGE;
                }
                pte = __pte(shp->shm_pages[idx]);
                if (pte_present(pte)) {
                        free_page (page); /* doesn't sleep */
                        goto done;
                }
                if (!pte_none(pte)) {
                        read_swap_page(pte_val(pte), (char *) page);
                        pte = __pte(shp->shm_pages[idx]);
                        if (pte_present(pte))  {
                                free_page (page); /* doesn't sleep */
                                goto done;
                        }
                        swap_free(pte_val(pte));
                        shm_swp--;
                }
                shm_rss++;
                pte = pte_mkdirty(mk_pte(page, PAGE_SHARED));
                shp->shm_pages[idx] = pte_val(pte);
        } else
                --current->maj_flt;  /* was incremented in do_no_page */

done:   /* pte_val(pte) == shp->shm_pages[idx] */
        current->min_flt++;
        atomic_inc(&mem_map[MAP_NR(pte_page(pte))].count);
        return pte_modify(pte, shmd->vm_page_prot);
}

/*
 * Goes through counter = (shm_rss >> prio) present shm pages.
 */
static unsigned long swap_id = 0; /* currently being swapped */
static unsigned long swap_idx = 0; /* next to swap */

int shm_swap (int prio, int dma)
{
        pte_t page;
        struct shmid_ds *shp;
        struct vm_area_struct *shmd;
        unsigned long swap_nr;
        unsigned long id, idx;
        int loop = 0;
        int counter;
        
        counter = shm_rss >> prio;
        if (!counter || !(swap_nr = get_swap_page()))
                return 0;

 check_id:
        shp = shm_segs[swap_id];
        if (shp == IPC_UNUSED || shp == IPC_NOID || shp->shm_perm.mode & SHM_LOCKED ) {
                next_id:
                swap_idx = 0;
                if (++swap_id > max_shmid) {
                        if (loop)
                                goto failed;
                        loop = 1;
                        swap_id = 0;
                }
                goto check_id;
        }
        id = swap_id;

 check_table:
        idx = swap_idx++;
        if (idx >= shp->shm_npages)
                goto next_id;

        page = __pte(shp->shm_pages[idx]);
        if (!pte_present(page))
                goto check_table;
        if (dma && !PageDMA(&mem_map[MAP_NR(pte_page(page))]))
                goto check_table;
        swap_attempts++;

        if (--counter < 0) { /* failed */
                failed:
                swap_free (swap_nr);
                return 0;
        }
        if (shp->attaches)
          for (shmd = shp->attaches; ; ) {
            do {
                pgd_t *page_dir;
                pmd_t *page_middle;
                pte_t *page_table, pte;
                unsigned long tmp;

                if ((SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK) != id) {
                        printk ("shm_swap: id=%ld does not match shmd->vm_pte.id=%ld\n",
                                id, SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK);
                        continue;
                }
                tmp = shmd->vm_start + (idx << PAGE_SHIFT) - shmd->vm_offset;
                if (!(tmp >= shmd->vm_start && tmp < shmd->vm_end))
                        continue;
                page_dir = pgd_offset(shmd->vm_mm,tmp);
                if (pgd_none(*page_dir) || pgd_bad(*page_dir)) {
                        printk("shm_swap: bad pgtbl! id=%ld start=%lx idx=%ld\n",
                                        id, shmd->vm_start, idx);
                        pgd_clear(page_dir);
                        continue;
                }
                page_middle = pmd_offset(page_dir,tmp);
                if (pmd_none(*page_middle) || pmd_bad(*page_middle)) {
                        printk("shm_swap: bad pgmid! id=%ld start=%lx idx=%ld\n",
                                        id, shmd->vm_start, idx);
                        pmd_clear(page_middle);
                        continue;
                }
                page_table = pte_offset(page_middle,tmp);
                pte = *page_table;
                if (!pte_present(pte))
                        continue;
                if (pte_young(pte)) {
                        set_pte(page_table, pte_mkold(pte));
                        continue;
                }
                if (pte_page(pte) != pte_page(page))
                        printk("shm_swap_out: page and pte mismatch %lx %lx\n",
                               pte_page(pte),pte_page(page));
                flush_cache_page(shmd, tmp);
                set_pte(page_table,
                  __pte(shmd->vm_pte + SWP_ENTRY(0, idx << SHM_IDX_SHIFT)));
                atomic_dec(&mem_map[MAP_NR(pte_page(pte))].count);
                if (shmd->vm_mm->rss > 0)
                        shmd->vm_mm->rss--;
                flush_tlb_page(shmd, tmp);
            /* continue looping through the linked list */
            } while (0);
            shmd = shmd->vm_next_share;
            if (!shmd)
                break;
        }

        if (atomic_read(&mem_map[MAP_NR(pte_page(page))].count) != 1)
                goto check_table;
        shp->shm_pages[idx] = swap_nr;
        write_swap_page (swap_nr, (char *) pte_page(page));
        free_page(pte_page(page));
        swap_successes++;
        shm_swp++;
        shm_rss--;
        return 1;
}