/*
 * linux/ipc/sem.c
 * Copyright (C) 1992 Krishna Balasubramanian
 * Copyright (C) 1995 Eric Schenk, Bruno Haible
 *
 * IMPLEMENTATION NOTES ON CODE REWRITE (Eric Schenk, January 1995):
 * This code underwent a massive rewrite in order to solve some problems
 * with the original code. In particular the original code failed to
 * wake up processes that were waiting for semval to go to 0 if the
 * value went to 0 and was then incremented rapidly enough. In solving
 * this problem I have also modified the implementation so that it
 * processes pending operations in a FIFO manner, thus give a guarantee
 * that processes waiting for a lock on the semaphore won't starve
 * unless another locking process fails to unlock.
 * In addition the following two changes in behavior have been introduced:
 * - The original implementation of semop returned the value
 *   last semaphore element examined on success. This does not
 *   match the manual page specifications, and effectively
 *   allows the user to read the semaphore even if they do not
 *   have read permissions. The implementation now returns 0
 *   on success as stated in the manual page.
 * - There is some confusion over whether the set of undo adjustments
 *   to be performed at exit should be done in an atomic manner.
 *   That is, if we are attempting to decrement the semval should we queue
 *   up and wait until we can do so legally?
 *   The original implementation attempted to do this.
 *   The current implementation does not do so. This is because I don't
 *   think it is the right thing (TM) to do, and because I couldn't
 *   see a clean way to get the old behavior with the new design.
 *   The POSIX standard and SVID should be consulted to determine
 *   what behavior is mandated.
 */

#include <linux/errno.h>
#include <asm/segment.h>
#include <linux/string.h>
#include <linux/sched.h>
#include <linux/sem.h>
#include <linux/ipc.h>
#include <linux/stat.h>
#include <linux/malloc.h>

extern int ipcperms (struct ipc_perm *ipcp, short semflg);
static int newary (key_t, int, int);
static int findkey (key_t key);
static void freeary (int id);

static struct semid_ds *semary[SEMMNI];
static int used_sems = 0, used_semids = 0;
static struct wait_queue *sem_lock = NULL;
static int max_semid = 0;

static unsigned short sem_seq = 0;

void sem_init (void)
{
        int i;

        sem_lock = NULL;
        used_sems = used_semids = max_semid = sem_seq = 0;
        for (i = 0; i < SEMMNI; i++)
                semary[i] = (struct semid_ds *) IPC_UNUSED;
        return;
}

static int findkey (key_t key)
{
        int id;
        struct semid_ds *sma;

        for (id = 0; id <= max_semid; id++) {
                while ((sma = semary[id]) == IPC_NOID)
                        interruptible_sleep_on (&sem_lock);
                if (sma == IPC_UNUSED)
                        continue;
                if (key == sma->sem_perm.key)
                        return id;
        }
        return -1;
}

static int newary (key_t key, int nsems, int semflg)
{
        int id;
        struct semid_ds *sma;
        struct ipc_perm *ipcp;
        int size;

        if (!nsems)
                return -EINVAL;
        if (used_sems + nsems > SEMMNS)
                return -ENOSPC;
        for (id = 0; id < SEMMNI; id++)
                if (semary[id] == IPC_UNUSED) {
                        semary[id] = (struct semid_ds *) IPC_NOID;
                        goto found;
                }
        return -ENOSPC;
found:
        size = sizeof (*sma) + nsems * sizeof (struct sem);
        used_sems += nsems;
        sma = (struct semid_ds *) kmalloc (size, GFP_KERNEL);
        if (!sma) {
                semary[id] = (struct semid_ds *) IPC_UNUSED;
                used_sems -= nsems;
                wake_up (&sem_lock);
                return -ENOMEM;
        }
        memset (sma, 0, size);
        sma->sem_base = (struct sem *) &sma[1];
        ipcp = &sma->sem_perm;
        ipcp->mode = (semflg & S_IRWXUGO);
        ipcp->key = key;
        ipcp->cuid = ipcp->uid = current->euid;
        ipcp->gid = ipcp->cgid = current->egid;
        sma->sem_perm.seq = sem_seq;
        /* sma->sem_pending = NULL; */
        sma->sem_pending_last = &sma->sem_pending;
        /* sma->undo = NULL; */
        sma->sem_nsems = nsems;
        sma->sem_ctime = CURRENT_TIME;
        if (id > max_semid)
                max_semid = id;
        used_semids++;
        semary[id] = sma;
        wake_up (&sem_lock);
        return (unsigned int) sma->sem_perm.seq * SEMMNI + id;
}

asmlinkage int sys_semget (key_t key, int nsems, int semflg)
{
        int id;
        struct semid_ds *sma;

        if (nsems < 0 || nsems > SEMMSL)
                return -EINVAL;
        if (key == IPC_PRIVATE)
                return newary(key, nsems, semflg);
        if ((id = findkey (key)) == -1) {  /* key not used */
                if (!(semflg & IPC_CREAT))
                        return -ENOENT;
                return newary(key, nsems, semflg);
        }
        if (semflg & IPC_CREAT && semflg & IPC_EXCL)
                return -EEXIST;
        sma = semary[id];
        if (nsems > sma->sem_nsems)
                return -EINVAL;
        if (ipcperms(&sma->sem_perm, semflg))
                return -EACCES;
        return (unsigned int) sma->sem_perm.seq * SEMMNI + id;
}

/* Manage the doubly linked list sma->sem_pending as a FIFO:
 * insert new queue elements at the tail sma->sem_pending_last.
 */
static inline void insert_into_queue (struct semid_ds * sma, struct sem_queue * q)
{
        *(q->prev = sma->sem_pending_last) = q;
        *(sma->sem_pending_last = &q->next) = NULL;
}
static inline void remove_from_queue (struct semid_ds * sma, struct sem_queue * q)
{
        *(q->prev) = q->next;
        if (q->next)
                q->next->prev = q->prev;
        else /* sma->sem_pending_last == &q->next */
                sma->sem_pending_last = q->prev;
        q->prev = NULL; /* mark as removed */
}

/* Determine whether a sequence of semaphore operations would succeed
 * all at once. Return 0 if yes, 1 if need to sleep, else return error code.
 */
static int try_semop (struct semid_ds * sma, struct sembuf * sops, int nsops)
{
        int result = 0;
        int i = 0;

        while (i < nsops) {
                struct sembuf * sop = &sops[i];
                struct sem * curr = &sma->sem_base[sop->sem_num];
                if (sop->sem_op + curr->semval > SEMVMX) {
                        result = -ERANGE;
                        break;
                }
                if (!sop->sem_op && curr->semval) {
                        if (sop->sem_flg & IPC_NOWAIT)
                                result = -EAGAIN;
                        else
                                result = 1;
                        break;
                }
                i++;
                curr->semval += sop->sem_op;
                if (curr->semval < 0) {
                        if (sop->sem_flg & IPC_NOWAIT)
                                result = -EAGAIN;
                        else
                                result = 1;
                        break;
                }
        }
        while (--i >= 0) {
                struct sembuf * sop = &sops[i];
                struct sem * curr = &sma->sem_base[sop->sem_num];
                curr->semval -= sop->sem_op;
        }
        return result;
}

/* Actually perform a sequence of semaphore operations. Atomically. */
/* This assumes that try_semop() already returned 0. */
static int do_semop (struct semid_ds * sma, struct sembuf * sops, int nsops,
                     struct sem_undo * un, int pid)
{
        int i;

        for (i = 0; i < nsops; i++) {
                struct sembuf * sop = &sops[i];
                struct sem * curr = &sma->sem_base[sop->sem_num];
                if (sop->sem_op + curr->semval > SEMVMX) {
                        printk("do_semop: race\n");
                        break;
                }
                if (!sop->sem_op) {
                        if (curr->semval) {
                                printk("do_semop: race\n");
                                break;
                        }
                } else {
                        curr->semval += sop->sem_op;
                        if (curr->semval < 0) {
                                printk("do_semop: race\n");
                                break;
                        }
                        if (sop->sem_flg & SEM_UNDO)
                                un->semadj[sop->sem_num] -= sop->sem_op;
                }
                curr->sempid = pid;
        }
        sma->sem_otime = CURRENT_TIME;

        /* Previous implementation returned the last semaphore's semval.
         * This is wrong because we may not have checked read permission,
         * only write permission.
         */
        return 0;
}

/* Go through the pending queue for the indicated semaphore
 * looking for tasks that can be completed. Keep cycling through
 * the queue until a pass is made in which no process is woken up.
 */
static void update_queue (struct semid_ds * sma)
{
        int wokeup, error;
        struct sem_queue * q;

        do {
                wokeup = 0;
                for (q = sma->sem_pending; q; q = q->next) {
                        error = try_semop(sma, q->sops, q->nsops);
                        /* Does q->sleeper still need to sleep? */
                        if (error > 0)
                                continue;
                        /* Perform the operations the sleeper was waiting for */
                        if (!error)
                                error = do_semop(sma, q->sops, q->nsops, q->undo, q->pid);
                        q->status = error;
                        /* Remove it from the queue */
                        remove_from_queue(sma,q);
                        /* Wake it up */
                        wake_up_interruptible(&q->sleeper); /* doesn't sleep! */
                        wokeup++;
                }
        } while (wokeup);
}

/* The following counts are associated to each semaphore:
 *   semncnt        number of tasks waiting on semval being nonzero
 *   semzcnt        number of tasks waiting on semval being zero
 * This model assumes that a task waits on exactly one semaphore.
 * Since semaphore operations are to be performed atomically, tasks actually
 * wait on a whole sequence of semaphores simultaneously.
 * The counts we return here are a rough approximation, but still
 * warrant that semncnt+semzcnt>0 if the task is on the pending queue.
 */
static int count_semncnt (struct semid_ds * sma, ushort semnum)
{
        int semncnt;
        struct sem_queue * q;

        semncnt = 0;
        for (q = sma->sem_pending; q; q = q->next) {
                struct sembuf * sops = q->sops;
                int nsops = q->nsops;
                int i;
                for (i = 0; i < nsops; i++)
                        if (sops[i].sem_num == semnum
                            && (sops[i].sem_op < 0)
                            && !(sops[i].sem_flg & IPC_NOWAIT))
                                semncnt++;
        }
        return semncnt;
}
static int count_semzcnt (struct semid_ds * sma, ushort semnum)
{
        int semzcnt;
        struct sem_queue * q;

        semzcnt = 0;
        for (q = sma->sem_pending; q; q = q->next) {
                struct sembuf * sops = q->sops;
                int nsops = q->nsops;
                int i;
                for (i = 0; i < nsops; i++)
                        if (sops[i].sem_num == semnum
                            && (sops[i].sem_op == 0)
                            && !(sops[i].sem_flg & IPC_NOWAIT))
                                semzcnt++;
        }
        return semzcnt;
}

/* Free a semaphore set. */
static void freeary (int id)
{
        struct semid_ds *sma = semary[id];
        struct sem_undo *un;
        struct sem_queue *q;

        /* Invalidate this semaphore set */
        sma->sem_perm.seq++;
        sem_seq = (sem_seq+1) % ((unsigned)(1<<31)/SEMMNI); /* increment, but avoid overflow */
        used_sems -= sma->sem_nsems;
        if (id == max_semid)
                while (max_semid && (semary[--max_semid] == IPC_UNUSED));
        semary[id] = (struct semid_ds *) IPC_UNUSED;
        used_semids--;

        /* Invalidate the existing undo structures for this semaphore set.
         * (They will be freed without any further action in sem_exit().)
         */
        for (un = sma->undo; un; un = un->id_next)
                un->semid = -1;

        /* Wake up all pending processes and let them fail with EIDRM. */
        for (q = sma->sem_pending; q; q = q->next) {
                q->status = -EIDRM;
                q->prev = NULL;
                wake_up_interruptible(&q->sleeper); /* doesn't sleep! */
        }

        kfree(sma);
}

asmlinkage int sys_semctl (int semid, int semnum, int cmd, union semun arg)
{
        struct semid_ds *buf = NULL;
        struct semid_ds tbuf;
        int i, id, val = 0;
        struct semid_ds *sma;
        struct ipc_perm *ipcp;
        struct sem *curr = NULL;
        struct sem_undo *un;
        unsigned int nsems;
        ushort *array = NULL;
        ushort sem_io[SEMMSL];

        if (semid < 0 || semnum < 0 || cmd < 0)
                return -EINVAL;

        switch (cmd) {
        case IPC_INFO:
        case SEM_INFO:
        {
                struct seminfo seminfo, *tmp = arg.__buf;
                seminfo.semmni = SEMMNI;
                seminfo.semmns = SEMMNS;
                seminfo.semmsl = SEMMSL;
                seminfo.semopm = SEMOPM;
                seminfo.semvmx = SEMVMX;
                seminfo.semmnu = SEMMNU;
                seminfo.semmap = SEMMAP;
                seminfo.semume = SEMUME;
                seminfo.semusz = SEMUSZ;
                seminfo.semaem = SEMAEM;
                if (cmd == SEM_INFO) {
                        seminfo.semusz = used_semids;
                        seminfo.semaem = used_sems;
                }
                i = verify_area(VERIFY_WRITE, tmp, sizeof(struct seminfo));
                if (i)
                        return i;
                memcpy_tofs (tmp, &seminfo, sizeof(struct seminfo));
                return max_semid;
        }

        case SEM_STAT:
                buf = arg.buf;
                i = verify_area (VERIFY_WRITE, buf, sizeof (*buf));
                if (i)
                        return i;
                if (semid > max_semid)
                        return -EINVAL;
                sma = semary[semid];
                if (sma == IPC_UNUSED || sma == IPC_NOID)
                        return -EINVAL;
                if (ipcperms (&sma->sem_perm, S_IRUGO))
                        return -EACCES;
                id = (unsigned int) sma->sem_perm.seq * SEMMNI + semid;
                tbuf.sem_perm   = sma->sem_perm;
                tbuf.sem_otime  = sma->sem_otime;
                tbuf.sem_ctime  = sma->sem_ctime;
                tbuf.sem_nsems  = sma->sem_nsems;
                memcpy_tofs (buf, &tbuf, sizeof(*buf));
                return id;
        }

        id = (unsigned int) semid % SEMMNI;
        sma = semary [id];
        if (sma == IPC_UNUSED || sma == IPC_NOID)
                return -EINVAL;
        ipcp = &sma->sem_perm;
        nsems = sma->sem_nsems;
        if (sma->sem_perm.seq != (unsigned int) semid / SEMMNI)
                return -EIDRM;

        switch (cmd) {
        case GETVAL:
        case GETPID:
        case GETNCNT:
        case GETZCNT:
        case SETVAL:
                if (semnum >= nsems)
                        return -EINVAL;
                curr = &sma->sem_base[semnum];
                break;
        }

        switch (cmd) {
        case GETVAL:
        case GETPID:
        case GETNCNT:
        case GETZCNT:
        case GETALL:
                if (ipcperms (ipcp, S_IRUGO))
                        return -EACCES;
                switch (cmd) {
                case GETVAL : return curr->semval;
                case GETPID : return curr->sempid;
                case GETNCNT: return count_semncnt(sma,semnum);
                case GETZCNT: return count_semzcnt(sma,semnum);
                case GETALL:
                        array = arg.array;
                        i = verify_area (VERIFY_WRITE, array, nsems*sizeof(ushort));
                        if (i)
                                return i;
                }
                break;
        case SETVAL:
                val = arg.val;
                if (val > SEMVMX || val < 0)
                        return -ERANGE;
                break;
        case IPC_RMID:
                if (suser() || current->euid == ipcp->cuid || current->euid == ipcp->uid) {
                        freeary (id);
                        return 0;
                }
                return -EPERM;
        case SETALL: /* arg is a pointer to an array of ushort */
                array = arg.array;
                if ((i = verify_area (VERIFY_READ, array, nsems*sizeof(ushort))))
                        return i;
                memcpy_fromfs (sem_io, array, nsems*sizeof(ushort));
                for (i = 0; i < nsems; i++)
                        if (sem_io[i] > SEMVMX)
                                return -ERANGE;
                break;
        case IPC_STAT:
                buf = arg.buf;
                if ((i = verify_area (VERIFY_WRITE, buf, sizeof(*buf))))
                        return i;
                break;
        case IPC_SET:
                buf = arg.buf;
                if ((i = verify_area (VERIFY_READ, buf, sizeof (*buf))))
                        return i;
                memcpy_fromfs (&tbuf, buf, sizeof (*buf));
                break;
        }

        if (semary[id] == IPC_UNUSED || semary[id] == IPC_NOID)
                return -EIDRM;
        if (sma->sem_perm.seq != (unsigned int) semid / SEMMNI)
                return -EIDRM;

        switch (cmd) {
        case GETALL:
                if (ipcperms (ipcp, S_IRUGO))
                        return -EACCES;
                for (i = 0; i < sma->sem_nsems; i++)
                        sem_io[i] = sma->sem_base[i].semval;
                memcpy_tofs (array, sem_io, nsems*sizeof(ushort));
                break;
        case SETVAL:
                if (ipcperms (ipcp, S_IWUGO))
                        return -EACCES;
                for (un = sma->undo; un; un = un->id_next)
                        un->semadj[semnum] = 0;
                curr->semval = val;
                sma->sem_ctime = CURRENT_TIME;
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
                break;
        case IPC_SET:
                if (suser() || current->euid == ipcp->cuid || current->euid == ipcp->uid) {
                        ipcp->uid = tbuf.sem_perm.uid;
                        ipcp->gid = tbuf.sem_perm.gid;
                        ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
                                | (tbuf.sem_perm.mode & S_IRWXUGO);
                        sma->sem_ctime = CURRENT_TIME;
                        return 0;
                }
                return -EPERM;
        case IPC_STAT:
                if (ipcperms (ipcp, S_IRUGO))
                        return -EACCES;
                tbuf.sem_perm   = sma->sem_perm;
                tbuf.sem_otime  = sma->sem_otime;
                tbuf.sem_ctime  = sma->sem_ctime;
                tbuf.sem_nsems  = sma->sem_nsems;
                memcpy_tofs (buf, &tbuf, sizeof(*buf));
                break;
        case SETALL:
                if (ipcperms (ipcp, S_IWUGO))
                        return -EACCES;
                for (i = 0; i < nsems; i++)
                        sma->sem_base[i].semval = sem_io[i];
                for (un = sma->undo; un; un = un->id_next)
                        for (i = 0; i < nsems; i++)
                                un->semadj[i] = 0;
                sma->sem_ctime = CURRENT_TIME;
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
                break;
        default:
                return -EINVAL;
        }
        return 0;
}

asmlinkage int sys_semop (int semid, struct sembuf *tsops, unsigned nsops)
{
        int i, id, size, error;
        struct semid_ds *sma;
        struct sembuf sops[SEMOPM], *sop;
        struct sem_undo *un;
        int undos = 0, alter = 0;

        if (nsops < 1 || semid < 0)
                return -EINVAL;
        if (nsops > SEMOPM)
                return -E2BIG;
        if (!tsops)
                return -EFAULT;
        if ((i = verify_area (VERIFY_READ, tsops, nsops * sizeof(*tsops))))
                return i;
        memcpy_fromfs (sops, tsops, nsops * sizeof(*tsops));
        id = (unsigned int) semid % SEMMNI;
        if ((sma = semary[id]) == IPC_UNUSED || sma == IPC_NOID)
                return -EINVAL;
        if (sma->sem_perm.seq != (unsigned int) semid / SEMMNI)
                return -EIDRM;
        for (i = 0; i < nsops; i++) {
                sop = &sops[i];
                if (sop->sem_num >= sma->sem_nsems)
                        return -EFBIG;
                if (sop->sem_flg & SEM_UNDO)
                        undos++;
                if (sop->sem_op)
                        alter++;
        }
        if (ipcperms(&sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
                return -EACCES;
        error = try_semop(sma, sops, nsops);
        if (error < 0)
                return error;
        if (undos) {
                /* Make sure we have an undo structure
                 * for this process and this semaphore set.
                 */
                for (un = current->semundo; un; un = un->proc_next)
                        if (un->semid == semid)
                                break;
                if (!un) {
                        size = sizeof(struct sem_undo) + sizeof(short)*sma->sem_nsems;
                        un = (struct sem_undo *) kmalloc(size, GFP_ATOMIC);
                        if (!un)
                                return -ENOMEM;
                        memset(un, 0, size);
                        un->semadj = (short *) &un[1];
                        un->semid = semid;
                        un->proc_next = current->semundo;
                        current->semundo = un;
                        un->id_next = sma->undo;
                        sma->undo = un;
                }
        } else
                un = NULL;
        if (error == 0) {
                /* the operations go through immediately */
                error = do_semop(sma, sops, nsops, un, current->pid);
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
                return error;
        } else {
                /* We need to sleep on this operation, so we put the current
                 * task into the pending queue and go to sleep.
                 */
                struct sem_queue queue;

                queue.sma = sma;
                queue.sops = sops;
                queue.nsops = nsops;
                queue.undo = un;
                queue.pid = current->pid;
                queue.status = 0;
                insert_into_queue(sma,&queue);
                queue.sleeper = NULL;
                current->semsleeping = &queue;
                interruptible_sleep_on(&queue.sleeper);
                current->semsleeping = NULL;
                /* When we wake up, either the operation is finished,
                 * or some kind of error happened.
                 */
                if (!queue.prev) {
                        /* operation is finished, update_queue() removed us */
                        return queue.status;
                } else {
                        remove_from_queue(sma,&queue);
                        return -EINTR;
                }
        }
}

/*
 * add semadj values to semaphores, free undo structures.
 * undo structures are not freed when semaphore arrays are destroyed
 * so some of them may be out of date.
 * IMPLEMENTATION NOTE: There is some confusion over whether the
 * set of adjustments that needs to be done should be done in an atomic
 * manner or not. That is, if we are attempting to decrement the semval
 * should we queue up and wait until we can do so legally?
 * The original implementation attempted to do this (queue and wait).
 * The current implementation does not do so. The POSIX standard
 * and SVID should be consulted to determine what behavior is mandated.
 */
void sem_exit (void)
{
        struct sem_queue *q;
        struct sem_undo *u, *un = NULL, **up, **unp;
        struct semid_ds *sma;
        int nsems, i;

        /* If the current process was sleeping for a semaphore,
         * remove it from the queue.
         */
        if ((q = current->semsleeping)) {
                if (q->prev)
                        remove_from_queue(q->sma,q);
                current->semsleeping = NULL;
        }

        for (up = &current->semundo; (u = *up); *up = u->proc_next, kfree(u)) {
                if (u->semid == -1)
                        continue;
                sma = semary[(unsigned int) u->semid % SEMMNI];
                if (sma == IPC_UNUSED || sma == IPC_NOID)
                        continue;
                if (sma->sem_perm.seq != (unsigned int) u->semid / SEMMNI)
                        continue;
                /* remove u from the sma->undo list */
                for (unp = &sma->undo; (un = *unp); unp = &un->id_next) {
                        if (u == un)
                                goto found;
                }
                printk ("sem_exit undo list error id=%d\n", u->semid);
                break;
found:
                *unp = un->id_next;
                /* perform adjustments registered in u */
                nsems = sma->sem_nsems;
                for (i = 0; i < nsems; i++) {
                        struct sem * sem = &sma->sem_base[i];
                        sem->semval += u->semadj[i];
                        if (sem->semval < 0)
                                sem->semval = 0; /* shouldn't happen */
                        sem->sempid = current->pid;
                }
                sma->sem_otime = CURRENT_TIME;
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
        }
        current->semundo = NULL;
}