/*
 * This file contains the procedures for the handling of select and poll
 *
 * Created for Linux based loosely upon Mathius Lattner's minix
 * patches by Peter MacDonald. Heavily edited by Linus.
 *
 *  4 February 1994
 *     COFF/ELF binary emulation. If the process has the STICKY_TIMEOUTS
 *     flag set in its personality we do *not* modify the given timeout
 *     parameter to reflect time remaining.
 *
 *  24 January 2000
 *     Changed sys_poll()/do_poll() to use PAGE_SIZE chunk-based allocation 
 *     of fds to overcome nfds < 16390 descriptors limit (Tigran Aivazian).
 */

#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/poll.h>
#include <linux/personality.h> /* for STICKY_TIMEOUTS */
#include <linux/file.h>

#include <asm/uaccess.h>

#define ROUND_UP(x,y) (((x)+(y)-1)/(y))
#define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)

struct poll_table_entry {
        struct file * filp;
        wait_queue_t wait;
        wait_queue_head_t * wait_address;
};

struct poll_table_page {
        struct poll_table_page * next;
        struct poll_table_entry * entry;
        struct poll_table_entry entries[0];
};

#define POLL_TABLE_FULL(table) \
        ((unsigned long)((table)->entry+1) > PAGE_SIZE + (unsigned long)(table))

/*
 * Ok, Peter made a complicated, but straightforward multiple_wait() function.
 * I have rewritten this, taking some shortcuts: This code may not be easy to
 * follow, but it should be free of race-conditions, and it's practical. If you
 * understand what I'm doing here, then you understand how the linux
 * sleep/wakeup mechanism works.
 *
 * Two very simple procedures, poll_wait() and poll_freewait() make all the
 * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
 * as all select/poll functions have to call it to add an entry to the
 * poll table.
 */

void poll_freewait(poll_table* pt)
{
        struct poll_table_page * p = pt->table;
        while (p) {
                struct poll_table_entry * entry;
                struct poll_table_page *old;

                entry = p->entry;
                do {
                        entry--;
                        remove_wait_queue(entry->wait_address,&entry->wait);
                        fput(entry->filp);
                } while (entry > p->entries);
                old = p;
                p = p->next;
                free_page((unsigned long) old);
        }
}

void __pollwait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
{
        struct poll_table_page *table = p->table;

        if (!table || POLL_TABLE_FULL(table)) {
                struct poll_table_page *new_table;

                new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
                if (!new_table) {
                        p->error = -ENOMEM;
                        __set_current_state(TASK_RUNNING);
                        return;
                }
                new_table->entry = new_table->entries;
                new_table->next = table;
                p->table = new_table;
                table = new_table;
        }

        /* Add a new entry */
        {
                struct poll_table_entry * entry = table->entry;
                table->entry = entry+1;
                get_file(filp);
                entry->filp = filp;
                entry->wait_address = wait_address;
                init_waitqueue_entry(&entry->wait, current);
                add_wait_queue(wait_address,&entry->wait);
        }
}

#define __IN(fds, n)            (fds->in + n)
#define __OUT(fds, n)           (fds->out + n)
#define __EX(fds, n)            (fds->ex + n)
#define __RES_IN(fds, n)        (fds->res_in + n)
#define __RES_OUT(fds, n)       (fds->res_out + n)
#define __RES_EX(fds, n)        (fds->res_ex + n)

#define BITS(fds, n)            (*__IN(fds, n)|*__OUT(fds, n)|*__EX(fds, n))

static int max_select_fd(unsigned long n, fd_set_bits *fds)
{
        unsigned long *open_fds;
        unsigned long set;
        int max;

        /* handle last in-complete long-word first */
        set = ~(~0UL << (n & (__NFDBITS-1)));
        n /= __NFDBITS;
        open_fds = current->files->open_fds->fds_bits+n;
        max = 0;
        if (set) {
                set &= BITS(fds, n);
                if (set) {
                        if (!(set & ~*open_fds))
                                goto get_max;
                        return -EBADF;
                }
        }
        while (n) {
                open_fds--;
                n--;
                set = BITS(fds, n);
                if (!set)
                        continue;
                if (set & ~*open_fds)
                        return -EBADF;
                if (max)
                        continue;
get_max:
                do {
                        max++;
                        set >>= 1;
                } while (set);
                max += n * __NFDBITS;
        }

        return max;
}

#define BIT(i)          (1UL << ((i)&(__NFDBITS-1)))
#define MEM(i,m)        ((m)+(unsigned)(i)/__NFDBITS)
#define ISSET(i,m)      (((i)&*(m)) != 0)
#define SET(i,m)        (*(m) |= (i))

#define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
#define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
#define POLLEX_SET (POLLPRI)

int do_select(int n, fd_set_bits *fds, long *timeout)
{
        poll_table table, *wait;
        int retval, i, off;
        long __timeout = *timeout;

        read_lock(&current->files->file_lock);
        retval = max_select_fd(n, fds);
        read_unlock(&current->files->file_lock);

        if (retval < 0)
                return retval;
        n = retval;

        poll_initwait(&table);
        wait = &table;
        if (!__timeout)
                wait = NULL;
        retval = 0;
        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                for (i = 0 ; i < n; i++) {
                        unsigned long bit = BIT(i);
                        unsigned long mask;
                        struct file *file;

                        off = i / __NFDBITS;
                        if (!(bit & BITS(fds, off)))
                                continue;
                        file = fget(i);
                        mask = POLLNVAL;
                        if (file) {
                                mask = DEFAULT_POLLMASK;
                                if (file->f_op && file->f_op->poll)
                                        mask = file->f_op->poll(file, wait);
                                fput(file);
                        }
                        if ((mask & POLLIN_SET) && ISSET(bit, __IN(fds,off))) {
                                SET(bit, __RES_IN(fds,off));
                                retval++;
                                wait = NULL;
                        }
                        if ((mask & POLLOUT_SET) && ISSET(bit, __OUT(fds,off))) {
                                SET(bit, __RES_OUT(fds,off));
                                retval++;
                                wait = NULL;
                        }
                        if ((mask & POLLEX_SET) && ISSET(bit, __EX(fds,off))) {
                                SET(bit, __RES_EX(fds,off));
                                retval++;
                                wait = NULL;
                        }
                }
                wait = NULL;
                if (retval || !__timeout || signal_pending(current))
                        break;
                if(table.error) {
                        retval = table.error;
                        break;
                }
                __timeout = schedule_timeout(__timeout);
        }
        current->state = TASK_RUNNING;

        poll_freewait(&table);

        /*
         * Up-to-date the caller timeout.
         */
        *timeout = __timeout;
        return retval;
}

static void *select_bits_alloc(int size)
{
        return kmalloc(6 * size, GFP_KERNEL);
}

static void select_bits_free(void *bits, int size)
{
        kfree(bits);
}

/*
 * We can actually return ERESTARTSYS instead of EINTR, but I'd
 * like to be certain this leads to no problems. So I return
 * EINTR just for safety.
 *
 * Update: ERESTARTSYS breaks at least the xview clock binary, so
 * I'm trying ERESTARTNOHAND which restart only when you want to.
 */
#define MAX_SELECT_SECONDS \
        ((unsigned long) (MAX_SCHEDULE_TIMEOUT / HZ)-1)

asmlinkage long
sys_select(int n, fd_set *inp, fd_set *outp, fd_set *exp, struct timeval *tvp)
{
        fd_set_bits fds;
        char *bits;
        long timeout;
        int ret, size, max_fdset;

        timeout = MAX_SCHEDULE_TIMEOUT;
        if (tvp) {
                time_t sec, usec;

                if ((ret = verify_area(VERIFY_READ, tvp, sizeof(*tvp)))
                    || (ret = __get_user(sec, &tvp->tv_sec))
                    || (ret = __get_user(usec, &tvp->tv_usec)))
                        goto out_nofds;

                ret = -EINVAL;
                if (sec < 0 || usec < 0)
                        goto out_nofds;

                if ((unsigned long) sec < MAX_SELECT_SECONDS) {
                        timeout = ROUND_UP(usec, 1000000/HZ);
                        timeout += sec * (unsigned long) HZ;
                }
        }

        ret = -EINVAL;
        if (n < 0)
                goto out_nofds;

        /* max_fdset can increase, so grab it once to avoid race */
        max_fdset = current->files->max_fdset;
        if (n > max_fdset)
                n = max_fdset;

        /*
         * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
         * since we used fdset we need to allocate memory in units of
         * long-words. 
         */
        ret = -ENOMEM;
        size = FDS_BYTES(n);
        bits = select_bits_alloc(size);
        if (!bits)
                goto out_nofds;
        fds.in      = (unsigned long *)  bits;
        fds.out     = (unsigned long *) (bits +   size);
        fds.ex      = (unsigned long *) (bits + 2*size);
        fds.res_in  = (unsigned long *) (bits + 3*size);
        fds.res_out = (unsigned long *) (bits + 4*size);
        fds.res_ex  = (unsigned long *) (bits + 5*size);

        if ((ret = get_fd_set(n, inp, fds.in)) ||
            (ret = get_fd_set(n, outp, fds.out)) ||
            (ret = get_fd_set(n, exp, fds.ex)))
                goto out;
        zero_fd_set(n, fds.res_in);
        zero_fd_set(n, fds.res_out);
        zero_fd_set(n, fds.res_ex);

        ret = do_select(n, &fds, &timeout);

        if (tvp && !(current->personality & STICKY_TIMEOUTS)) {
                time_t sec = 0, usec = 0;
                if (timeout) {
                        sec = timeout / HZ;
                        usec = timeout % HZ;
                        usec *= (1000000/HZ);
                }
                put_user(sec, &tvp->tv_sec);
                put_user(usec, &tvp->tv_usec);
        }

        if (ret < 0)
                goto out;
        if (!ret) {
                ret = -ERESTARTNOHAND;
                if (signal_pending(current))
                        goto out;
                ret = 0;
        }

        set_fd_set(n, inp, fds.res_in);
        set_fd_set(n, outp, fds.res_out);
        set_fd_set(n, exp, fds.res_ex);

out:
        select_bits_free(bits, size);
out_nofds:
        return ret;
}

#define POLLFD_PER_PAGE  ((PAGE_SIZE) / sizeof(struct pollfd))

static void do_pollfd(unsigned int num, struct pollfd * fdpage,
        poll_table ** pwait, int *count)
{
        int i;

        for (i = 0; i < num; i++) {
                int fd;
                unsigned int mask;
                struct pollfd *fdp;

                mask = 0;
                fdp = fdpage+i;
                fd = fdp->fd;
                if (fd >= 0) {
                        struct file * file = fget(fd);
                        mask = POLLNVAL;
                        if (file != NULL) {
                                mask = DEFAULT_POLLMASK;
                                if (file->f_op && file->f_op->poll)
                                        mask = file->f_op->poll(file, *pwait);
                                mask &= fdp->events | POLLERR | POLLHUP;
                                fput(file);
                        }
                        if (mask) {
                                *pwait = NULL;
                                (*count)++;
                        }
                }
                fdp->revents = mask;
        }
}

static int do_poll(unsigned int nfds, unsigned int nchunks, unsigned int nleft, 
        struct pollfd *fds[], poll_table *wait, long timeout)
{
        int count;
        poll_table* pt = wait;

        for (;;) {
                unsigned int i;

                set_current_state(TASK_INTERRUPTIBLE);
                count = 0;
                for (i=0; i < nchunks; i++)
                        do_pollfd(POLLFD_PER_PAGE, fds[i], &pt, &count);
                if (nleft)
                        do_pollfd(nleft, fds[nchunks], &pt, &count);
                pt = NULL;
                if (count || !timeout || signal_pending(current))
                        break;
                count = wait->error;
                if (count)
                        break;
                timeout = schedule_timeout(timeout);
        }
        current->state = TASK_RUNNING;
        return count;
}

asmlinkage long sys_poll(struct pollfd * ufds, unsigned int nfds, long timeout)
{
        int i, j, fdcount, err;
        struct pollfd **fds;
        poll_table table, *wait;
        int nchunks, nleft;

        /* Do a sanity check on nfds ... */
        if (nfds > NR_OPEN)
                return -EINVAL;

        if (timeout) {
                /* Careful about overflow in the intermediate values */
                if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ)
                        timeout = (unsigned long)(timeout*HZ+999)/1000+1;
                else /* Negative or overflow */
                        timeout = MAX_SCHEDULE_TIMEOUT;
        }

        poll_initwait(&table);
        wait = &table;
        if (!timeout)
                wait = NULL;

        err = -ENOMEM;
        fds = NULL;
        if (nfds != 0) {
                fds = (struct pollfd **)kmalloc(
                        (1 + (nfds - 1) / POLLFD_PER_PAGE) * sizeof(struct pollfd *),
                        GFP_KERNEL);
                if (fds == NULL)
                        goto out;
        }

        nchunks = 0;
        nleft = nfds;
        while (nleft > POLLFD_PER_PAGE) { /* allocate complete PAGE_SIZE chunks */
                fds[nchunks] = (struct pollfd *)__get_free_page(GFP_KERNEL);
                if (fds[nchunks] == NULL)
                        goto out_fds;
                nchunks++;
                nleft -= POLLFD_PER_PAGE;
        }
        if (nleft) { /* allocate last PAGE_SIZE chunk, only nleft elements used */
                fds[nchunks] = (struct pollfd *)__get_free_page(GFP_KERNEL);
                if (fds[nchunks] == NULL)
                        goto out_fds;
        }

        err = -EFAULT;
        for (i=0; i < nchunks; i++)
                if (copy_from_user(fds[i], ufds + i*POLLFD_PER_PAGE, PAGE_SIZE))
                        goto out_fds1;
        if (nleft) {
                if (copy_from_user(fds[nchunks], ufds + nchunks*POLLFD_PER_PAGE, 
                                nleft * sizeof(struct pollfd)))
                        goto out_fds1;
        }

        fdcount = do_poll(nfds, nchunks, nleft, fds, wait, timeout);

        /* OK, now copy the revents fields back to user space. */
        for(i=0; i < nchunks; i++)
                for (j=0; j < POLLFD_PER_PAGE; j++, ufds++)
                        __put_user((fds[i] + j)->revents, &ufds->revents);
        if (nleft)
                for (j=0; j < nleft; j++, ufds++)
                        __put_user((fds[nchunks] + j)->revents, &ufds->revents);

        err = fdcount;
        if (!fdcount && signal_pending(current))
                err = -EINTR;

out_fds1:
        if (nleft)
                free_page((unsigned long)(fds[nchunks]));
out_fds:
        for (i=0; i < nchunks; i++)
                free_page((unsigned long)(fds[i]));
        if (nfds != 0)
                kfree(fds);
out:
        poll_freewait(&table);
        return err;
}