#include <linux/bitmap.h>
#include <linux/export.h>
#include <linux/idr.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
static DEFINE_SPINLOCK(simple_ida_lock);

/**
 * idr_alloc - allocate an id
 * @idr: idr handle
 * @ptr: pointer to be associated with the new id
 * @start: the minimum id (inclusive)
 * @end: the maximum id (exclusive)
 * @gfp: memory allocation flags
 *
 * Allocates an unused ID in the range [start, end).  Returns -ENOSPC
 * if there are no unused IDs in that range.
 *
 * Note that @end is treated as max when <= 0.  This is to always allow
 * using @start + N as @end as long as N is inside integer range.
 *
 * Simultaneous modifications to the @idr are not allowed and should be
 * prevented by the user, usually with a lock.  idr_alloc() may be called
 * concurrently with read-only accesses to the @idr, such as idr_find() and
 * idr_for_each_entry().
 */
int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
        void __rcu **slot;
        struct radix_tree_iter iter;

        if (WARN_ON_ONCE(start < 0))
                return -EINVAL;
        if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
                return -EINVAL;

        radix_tree_iter_init(&iter, start);
        slot = idr_get_free(&idr->idr_rt, &iter, gfp, end);
        if (IS_ERR(slot))
                return PTR_ERR(slot);

        radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
        radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);
        return iter.index;
}
EXPORT_SYMBOL_GPL(idr_alloc);

/**
 * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
 * @idr: idr handle
 * @ptr: pointer to be associated with the new id
 * @start: the minimum id (inclusive)
 * @end: the maximum id (exclusive)
 * @gfp: memory allocation flags
 *
 * Allocates an ID larger than the last ID allocated if one is available.
 * If not, it will attempt to allocate the smallest ID that is larger or
 * equal to @start.
 */
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
        int id, curr = idr->idr_next;

        if (curr < start)
                curr = start;

        id = idr_alloc(idr, ptr, curr, end, gfp);
        if ((id == -ENOSPC) && (curr > start))
                id = idr_alloc(idr, ptr, start, curr, gfp);

        if (id >= 0)
                idr->idr_next = id + 1U;

        return id;
}
EXPORT_SYMBOL(idr_alloc_cyclic);

/**
 * idr_for_each - iterate through all stored pointers
 * @idr: idr handle
 * @fn: function to be called for each pointer
 * @data: data passed to callback function
 *
 * The callback function will be called for each entry in @idr, passing
 * the id, the pointer and the data pointer passed to this function.
 *
 * If @fn returns anything other than %0, the iteration stops and that
 * value is returned from this function.
 *
 * idr_for_each() can be called concurrently with idr_alloc() and
 * idr_remove() if protected by RCU.  Newly added entries may not be
 * seen and deleted entries may be seen, but adding and removing entries
 * will not cause other entries to be skipped, nor spurious ones to be seen.
 */
int idr_for_each(const struct idr *idr,
                int (*fn)(int id, void *p, void *data), void *data)
{
        struct radix_tree_iter iter;
        void __rcu **slot;

        radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
                int ret = fn(iter.index, rcu_dereference_raw(*slot), data);
                if (ret)
                        return ret;
        }

        return 0;
}
EXPORT_SYMBOL(idr_for_each);

/**
 * idr_get_next - Find next populated entry
 * @idr: idr handle
 * @nextid: Pointer to lowest possible ID to return
 *
 * Returns the next populated entry in the tree with an ID greater than
 * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 * to the ID of the found value.  To use in a loop, the value pointed to by
 * nextid must be incremented by the user.
 */
void *idr_get_next(struct idr *idr, int *nextid)
{
        struct radix_tree_iter iter;
        void __rcu **slot;

        slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
        if (!slot)
                return NULL;

        *nextid = iter.index;
        return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next);

/**
 * idr_replace - replace pointer for given id
 * @idr: idr handle
 * @ptr: New pointer to associate with the ID
 * @id: Lookup key
 *
 * Replace the pointer registered with an ID and return the old value.
 * This function can be called under the RCU read lock concurrently with
 * idr_alloc() and idr_remove() (as long as the ID being removed is not
 * the one being replaced!).
 *
 * Returns: 0 on success.  %-ENOENT indicates that @id was not found.
 * %-EINVAL indicates that @id or @ptr were not valid.
 */
void *idr_replace(struct idr *idr, void *ptr, int id)
{
        struct radix_tree_node *node;
        void __rcu **slot = NULL;
        void *entry;

        if (WARN_ON_ONCE(id < 0))
                return ERR_PTR(-EINVAL);
        if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
                return ERR_PTR(-EINVAL);

        entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
        if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
                return ERR_PTR(-ENOENT);

        __radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);

        return entry;
}
EXPORT_SYMBOL(idr_replace);

/**
 * DOC: IDA description
 *
 * The IDA is an ID allocator which does not provide the ability to
 * associate an ID with a pointer.  As such, it only needs to store one
 * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
 * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
 * then initialise it using ida_init()).  To allocate a new ID, call
 * ida_simple_get().  To free an ID, call ida_simple_remove().
 *
 * If you have more complex locking requirements, use a loop around
 * ida_pre_get() and ida_get_new() to allocate a new ID.  Then use
 * ida_remove() to free an ID.  You must make sure that ida_get_new() and
 * ida_remove() cannot be called at the same time as each other for the
 * same IDA.
 *
 * You can also use ida_get_new_above() if you need an ID to be allocated
 * above a particular number.  ida_destroy() can be used to dispose of an
 * IDA without needing to free the individual IDs in it.  You can use
 * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
 *
 * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
 * limitation, it should be quite straightforward to raise the maximum.
 */

/*
 * Developer's notes:
 *
 * The IDA uses the functionality provided by the IDR & radix tree to store
 * bitmaps in each entry.  The IDR_FREE tag means there is at least one bit
 * free, unlike the IDR where it means at least one entry is free.
 *
 * I considered telling the radix tree that each slot is an order-10 node
 * and storing the bit numbers in the radix tree, but the radix tree can't
 * allow a single multiorder entry at index 0, which would significantly
 * increase memory consumption for the IDA.  So instead we divide the index
 * by the number of bits in the leaf bitmap before doing a radix tree lookup.
 *
 * As an optimisation, if there are only a few low bits set in any given
 * leaf, instead of allocating a 128-byte bitmap, we use the 'exceptional
 * entry' functionality of the radix tree to store BITS_PER_LONG - 2 bits
 * directly in the entry.  By being really tricksy, we could store
 * BITS_PER_LONG - 1 bits, but there're diminishing returns after optimising
 * for 0-3 allocated IDs.
 *
 * We allow the radix tree 'exceptional' count to get out of date.  Nothing
 * in the IDA nor the radix tree code checks it.  If it becomes important
 * to maintain an accurate exceptional count, switch the rcu_assign_pointer()
 * calls to radix_tree_iter_replace() which will correct the exceptional
 * count.
 *
 * The IDA always requires a lock to alloc/free.  If we add a 'test_bit'
 * equivalent, it will still need locking.  Going to RCU lookup would require
 * using RCU to free bitmaps, and that's not trivial without embedding an
 * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
 * bitmap, which is excessive.
 */

#define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)

/**
 * ida_get_new_above - allocate new ID above or equal to a start id
 * @ida: ida handle
 * @start: id to start search at
 * @id: pointer to the allocated handle
 *
 * Allocate new ID above or equal to @start.  It should be called
 * with any required locks to ensure that concurrent calls to
 * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
 * Consider using ida_simple_get() if you do not have complex locking
 * requirements.
 *
 * If memory is required, it will return %-EAGAIN, you should unlock
 * and go back to the ida_pre_get() call.  If the ida is full, it will
 * return %-ENOSPC.  On success, it will return 0.
 *
 * @id returns a value in the range @start ... %0x7fffffff.
 */
int ida_get_new_above(struct ida *ida, int start, int *id)
{
        struct radix_tree_root *root = &ida->ida_rt;
        void __rcu **slot;
        struct radix_tree_iter iter;
        struct ida_bitmap *bitmap;
        unsigned long index;
        unsigned bit, ebit;
        int new;

        index = start / IDA_BITMAP_BITS;
        bit = start % IDA_BITMAP_BITS;
        ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;

        slot = radix_tree_iter_init(&iter, index);
        for (;;) {
                if (slot)
                        slot = radix_tree_next_slot(slot, &iter,
                                                RADIX_TREE_ITER_TAGGED);
                if (!slot) {
                        slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
                        if (IS_ERR(slot)) {
                                if (slot == ERR_PTR(-ENOMEM))
                                        return -EAGAIN;
                                return PTR_ERR(slot);
                        }
                }
                if (iter.index > index) {
                        bit = 0;
                        ebit = RADIX_TREE_EXCEPTIONAL_SHIFT;
                }
                new = iter.index * IDA_BITMAP_BITS;
                bitmap = rcu_dereference_raw(*slot);
                if (radix_tree_exception(bitmap)) {
                        unsigned long tmp = (unsigned long)bitmap;
                        ebit = find_next_zero_bit(&tmp, BITS_PER_LONG, ebit);
                        if (ebit < BITS_PER_LONG) {
                                tmp |= 1UL << ebit;
                                rcu_assign_pointer(*slot, (void *)tmp);
                                *id = new + ebit - RADIX_TREE_EXCEPTIONAL_SHIFT;
                                return 0;
                        }
                        bitmap = this_cpu_xchg(ida_bitmap, NULL);
                        if (!bitmap)
                                return -EAGAIN;
                        memset(bitmap, 0, sizeof(*bitmap));
                        bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
                        rcu_assign_pointer(*slot, bitmap);
                }

                if (bitmap) {
                        bit = find_next_zero_bit(bitmap->bitmap,
                                                        IDA_BITMAP_BITS, bit);
                        new += bit;
                        if (new < 0)
                                return -ENOSPC;
                        if (bit == IDA_BITMAP_BITS)
                                continue;

                        __set_bit(bit, bitmap->bitmap);
                        if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
                                radix_tree_iter_tag_clear(root, &iter,
                                                                IDR_FREE);
                } else {
                        new += bit;
                        if (new < 0)
                                return -ENOSPC;
                        if (ebit < BITS_PER_LONG) {
                                bitmap = (void *)((1UL << ebit) |
                                                RADIX_TREE_EXCEPTIONAL_ENTRY);
                                radix_tree_iter_replace(root, &iter, slot,
                                                bitmap);
                                *id = new;
                                return 0;
                        }
                        bitmap = this_cpu_xchg(ida_bitmap, NULL);
                        if (!bitmap)
                                return -EAGAIN;
                        memset(bitmap, 0, sizeof(*bitmap));
                        __set_bit(bit, bitmap->bitmap);
                        radix_tree_iter_replace(root, &iter, slot, bitmap);
                }

                *id = new;
                return 0;
        }
}
EXPORT_SYMBOL(ida_get_new_above);

/**
 * ida_remove - Free the given ID
 * @ida: ida handle
 * @id: ID to free
 *
 * This function should not be called at the same time as ida_get_new_above().
 */
void ida_remove(struct ida *ida, int id)
{
        unsigned long index = id / IDA_BITMAP_BITS;
        unsigned offset = id % IDA_BITMAP_BITS;
        struct ida_bitmap *bitmap;
        unsigned long *btmp;
        struct radix_tree_iter iter;
        void __rcu **slot;

        slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
        if (!slot)
                goto err;

        bitmap = rcu_dereference_raw(*slot);
        if (radix_tree_exception(bitmap)) {
                btmp = (unsigned long *)slot;
                offset += RADIX_TREE_EXCEPTIONAL_SHIFT;
                if (offset >= BITS_PER_LONG)
                        goto err;
        } else {
                btmp = bitmap->bitmap;
        }
        if (!test_bit(offset, btmp))
                goto err;

        __clear_bit(offset, btmp);
        radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);
        if (radix_tree_exception(bitmap)) {
                if (rcu_dereference_raw(*slot) ==
                                        (void *)RADIX_TREE_EXCEPTIONAL_ENTRY)
                        radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
        } else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) {
                kfree(bitmap);
                radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
        }
        return;
 err:
        WARN(1, "ida_remove called for id=%d which is not allocated.\n", id);
}
EXPORT_SYMBOL(ida_remove);

/**
 * ida_destroy - Free the contents of an ida
 * @ida: ida handle
 *
 * Calling this function releases all resources associated with an IDA.  When
 * this call returns, the IDA is empty and can be reused or freed.  The caller
 * should not allow ida_remove() or ida_get_new_above() to be called at the
 * same time.
 */
void ida_destroy(struct ida *ida)
{
        struct radix_tree_iter iter;
        void __rcu **slot;

        radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
                struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
                if (!radix_tree_exception(bitmap))
                        kfree(bitmap);
                radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
        }
}
EXPORT_SYMBOL(ida_destroy);

/**
 * ida_simple_get - get a new id.
 * @ida: the (initialized) ida.
 * @start: the minimum id (inclusive, < 0x8000000)
 * @end: the maximum id (exclusive, < 0x8000000 or 0)
 * @gfp_mask: memory allocation flags
 *
 * Allocates an id in the range start <= id < end, or returns -ENOSPC.
 * On memory allocation failure, returns -ENOMEM.
 *
 * Compared to ida_get_new_above() this function does its own locking, and
 * should be used unless there are special requirements.
 *
 * Use ida_simple_remove() to get rid of an id.
 */
int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
                   gfp_t gfp_mask)
{
        int ret, id;
        unsigned int max;
        unsigned long flags;

        BUG_ON((int)start < 0);
        BUG_ON((int)end < 0);

        if (end == 0)
                max = 0x80000000;
        else {
                BUG_ON(end < start);
                max = end - 1;
        }

again:
        if (!ida_pre_get(ida, gfp_mask))
                return -ENOMEM;

        spin_lock_irqsave(&simple_ida_lock, flags);
        ret = ida_get_new_above(ida, start, &id);
        if (!ret) {
                if (id > max) {
                        ida_remove(ida, id);
                        ret = -ENOSPC;
                } else {
                        ret = id;
                }
        }
        spin_unlock_irqrestore(&simple_ida_lock, flags);

        if (unlikely(ret == -EAGAIN))
                goto again;

        return ret;
}
EXPORT_SYMBOL(ida_simple_get);

/**
 * ida_simple_remove - remove an allocated id.
 * @ida: the (initialized) ida.
 * @id: the id returned by ida_simple_get.
 *
 * Use to release an id allocated with ida_simple_get().
 *
 * Compared to ida_remove() this function does its own locking, and should be
 * used unless there are special requirements.
 */
void ida_simple_remove(struct ida *ida, unsigned int id)
{
        unsigned long flags;

        BUG_ON((int)id < 0);
        spin_lock_irqsave(&simple_ida_lock, flags);
        ida_remove(ida, id);
        spin_unlock_irqrestore(&simple_ida_lock, flags);
}
EXPORT_SYMBOL(ida_simple_remove);