/*
 *  linux/fs/file.c
 *
 *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
 *
 *  Manage the dynamic fd arrays in the process files_struct.
 */

#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/file.h>
#include <linux/bitops.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>

struct fdtable_defer {
        spinlock_t lock;
        struct work_struct wq;
        struct fdtable *next;
};

/*
 * We use this list to defer free fdtables that have vmalloced
 * sets/arrays. By keeping a per-cpu list, we avoid having to embed
 * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
 * this per-task structure.
 */
static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);

static inline void * alloc_fdmem(unsigned int size)
{
        if (size <= PAGE_SIZE)
                return kmalloc(size, GFP_KERNEL);
        else
                return vmalloc(size);
}

static inline void free_fdarr(struct fdtable *fdt)
{
        if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
                kfree(fdt->fd);
        else
                vfree(fdt->fd);
}

static inline void free_fdset(struct fdtable *fdt)
{
        if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
                kfree(fdt->open_fds);
        else
                vfree(fdt->open_fds);
}

static void free_fdtable_work(struct work_struct *work)
{
        struct fdtable_defer *f =
                container_of(work, struct fdtable_defer, wq);
        struct fdtable *fdt;

        spin_lock_bh(&f->lock);
        fdt = f->next;
        f->next = NULL;
        spin_unlock_bh(&f->lock);
        while(fdt) {
                struct fdtable *next = fdt->next;
                vfree(fdt->fd);
                free_fdset(fdt);
                kfree(fdt);
                fdt = next;
        }
}

void free_fdtable_rcu(struct rcu_head *rcu)
{
        struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
        struct fdtable_defer *fddef;

        BUG_ON(!fdt);

        if (fdt->max_fds <= NR_OPEN_DEFAULT) {
                /*
                 * This fdtable is embedded in the files structure and that
                 * structure itself is getting destroyed.
                 */
                kmem_cache_free(files_cachep,
                                container_of(fdt, struct files_struct, fdtab));
                return;
        }
        if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
                kfree(fdt->fd);
                kfree(fdt->open_fds);
                kfree(fdt);
        } else {
                fddef = &get_cpu_var(fdtable_defer_list);
                spin_lock(&fddef->lock);
                fdt->next = fddef->next;
                fddef->next = fdt;
                /* vmallocs are handled from the workqueue context */
                schedule_work(&fddef->wq);
                spin_unlock(&fddef->lock);
                put_cpu_var(fdtable_defer_list);
        }
}

/*
 * Expand the fdset in the files_struct.  Called with the files spinlock
 * held for write.
 */
static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
{
        unsigned int cpy, set;

        BUG_ON(nfdt->max_fds < ofdt->max_fds);
        if (ofdt->max_fds == 0)
                return;

        cpy = ofdt->max_fds * sizeof(struct file *);
        set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
        memcpy(nfdt->fd, ofdt->fd, cpy);
        memset((char *)(nfdt->fd) + cpy, 0, set);

        cpy = ofdt->max_fds / BITS_PER_BYTE;
        set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
        memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
        memset((char *)(nfdt->open_fds) + cpy, 0, set);
        memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
        memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
}

static struct fdtable * alloc_fdtable(unsigned int nr)
{
        struct fdtable *fdt;
        char *data;

        /*
         * Figure out how many fds we actually want to support in this fdtable.
         * Allocation steps are keyed to the size of the fdarray, since it
         * grows far faster than any of the other dynamic data. We try to fit
         * the fdarray into comfortable page-tuned chunks: starting at 1024B
         * and growing in powers of two from there on.
         */
        nr /= (1024 / sizeof(struct file *));
        nr = roundup_pow_of_two(nr + 1);
        nr *= (1024 / sizeof(struct file *));
        if (nr > NR_OPEN)
                nr = NR_OPEN;

        fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
        if (!fdt)
                goto out;
        fdt->max_fds = nr;
        data = alloc_fdmem(nr * sizeof(struct file *));
        if (!data)
                goto out_fdt;
        fdt->fd = (struct file **)data;
        data = alloc_fdmem(max_t(unsigned int,
                                 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
        if (!data)
                goto out_arr;
        fdt->open_fds = (fd_set *)data;
        data += nr / BITS_PER_BYTE;
        fdt->close_on_exec = (fd_set *)data;
        INIT_RCU_HEAD(&fdt->rcu);
        fdt->next = NULL;

        return fdt;

out_arr:
        free_fdarr(fdt);
out_fdt:
        kfree(fdt);
out:
        return NULL;
}

/*
 * Expand the file descriptor table.
 * This function will allocate a new fdtable and both fd array and fdset, of
 * the given size.
 * Return <0 error code on error; 1 on successful completion.
 * The files->file_lock should be held on entry, and will be held on exit.
 */
static int expand_fdtable(struct files_struct *files, int nr)
        __releases(files->file_lock)
        __acquires(files->file_lock)
{
        struct fdtable *new_fdt, *cur_fdt;

        spin_unlock(&files->file_lock);
        new_fdt = alloc_fdtable(nr);
        spin_lock(&files->file_lock);
        if (!new_fdt)
                return -ENOMEM;
        /*
         * Check again since another task may have expanded the fd table while
         * we dropped the lock
         */
        cur_fdt = files_fdtable(files);
        if (nr >= cur_fdt->max_fds) {
                /* Continue as planned */
                copy_fdtable(new_fdt, cur_fdt);
                rcu_assign_pointer(files->fdt, new_fdt);
                if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
                        free_fdtable(cur_fdt);
        } else {
                /* Somebody else expanded, so undo our attempt */
                free_fdarr(new_fdt);
                free_fdset(new_fdt);
                kfree(new_fdt);
        }
        return 1;
}

/*
 * Expand files.
 * This function will expand the file structures, if the requested size exceeds
 * the current capacity and there is room for expansion.
 * Return <0 error code on error; 0 when nothing done; 1 when files were
 * expanded and execution may have blocked.
 * The files->file_lock should be held on entry, and will be held on exit.
 */
int expand_files(struct files_struct *files, int nr)
{
        struct fdtable *fdt;

        fdt = files_fdtable(files);
        /* Do we need to expand? */
        if (nr < fdt->max_fds)
                return 0;
        /* Can we expand? */
        if (nr >= NR_OPEN)
                return -EMFILE;

        /* All good, so we try */
        return expand_fdtable(files, nr);
}

static void __devinit fdtable_defer_list_init(int cpu)
{
        struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
        spin_lock_init(&fddef->lock);
        INIT_WORK(&fddef->wq, free_fdtable_work);
        fddef->next = NULL;
}

void __init files_defer_init(void)
{
        int i;
        for_each_possible_cpu(i)
                fdtable_defer_list_init(i);
}