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

DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);

/**
 * idr_alloc_u32() - Allocate an ID.
 * @idr: IDR handle.
 * @ptr: Pointer to be associated with the new ID.
 * @nextid: Pointer to an ID.
 * @max: The maximum ID to allocate (inclusive).
 * @gfp: Memory allocation flags.
 *
 * Allocates an unused ID in the range specified by @nextid and @max.
 * Note that @max is inclusive whereas the @end parameter to idr_alloc()
 * is exclusive.  The new ID is assigned to @nextid before the pointer
 * is inserted into the IDR, so if @nextid points into the object pointed
 * to by @ptr, a concurrent lookup will not find an uninitialised ID.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: 0 if an ID was allocated, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.  If an error occurred,
 * @nextid is unchanged.
 */
int idr_alloc_u32(struct idr *idr, void *ptr, u32 *nextid,
                        unsigned long max, gfp_t gfp)
{
        struct radix_tree_iter iter;
        void __rcu **slot;
        unsigned int base = idr->idr_base;
        unsigned int id = *nextid;

        if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
                return -EINVAL;
        if (WARN_ON_ONCE(!(idr->idr_rt.gfp_mask & ROOT_IS_IDR)))
                idr->idr_rt.gfp_mask |= IDR_RT_MARKER;

        id = (id < base) ? 0 : id - base;
        radix_tree_iter_init(&iter, id);
        slot = idr_get_free(&idr->idr_rt, &iter, gfp, max - base);
        if (IS_ERR(slot))
                return PTR_ERR(slot);

        *nextid = iter.index + base;
        /* there is a memory barrier inside radix_tree_iter_replace() */
        radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
        radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);

        return 0;
}
EXPORT_SYMBOL_GPL(idr_alloc_u32);

/**
 * 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 specified by @start and @end.  If
 * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 * callers to use @start + N as @end as long as N is within integer range.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.
 */
int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
        u32 id = start;
        int ret;

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

        ret = idr_alloc_u32(idr, ptr, &id, end > 0 ? end - 1 : INT_MAX, gfp);
        if (ret)
                return ret;

        return id;
}
EXPORT_SYMBOL_GPL(idr_alloc);

/**
 * idr_alloc_cyclic() - Allocate an ID cyclically.
 * @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 specified by @nextid and @end.  If
 * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 * callers to use @start + N as @end as long as N is within integer range.
 * The search for an unused ID will start at the last ID allocated and will
 * wrap around to @start if no free IDs are found before reaching @end.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.
 */
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
        u32 id = idr->idr_next;
        int err, max = end > 0 ? end - 1 : INT_MAX;

        if ((int)id < start)
                id = start;

        err = idr_alloc_u32(idr, ptr, &id, max, gfp);
        if ((err == -ENOSPC) && (id > start)) {
                id = start;
                err = idr_alloc_u32(idr, ptr, &id, max, gfp);
        }
        if (err)
                return err;

        idr->idr_next = id + 1;
        return id;
}
EXPORT_SYMBOL(idr_alloc_cyclic);

/**
 * idr_remove() - Remove an ID from the IDR.
 * @idr: IDR handle.
 * @id: Pointer ID.
 *
 * Removes this ID from the IDR.  If the ID was not previously in the IDR,
 * this function returns %NULL.
 *
 * Since this function modifies the IDR, the caller should provide their
 * own locking to ensure that concurrent modification of the same IDR is
 * not possible.
 *
 * Return: The pointer formerly associated with this ID.
 */
void *idr_remove(struct idr *idr, unsigned long id)
{
        return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
}
EXPORT_SYMBOL_GPL(idr_remove);

/**
 * idr_find() - Return pointer for given ID.
 * @idr: IDR handle.
 * @id: Pointer ID.
 *
 * Looks up the pointer associated with this ID.  A %NULL pointer may
 * indicate that @id is not allocated or that the %NULL pointer was
 * associated with this ID.
 *
 * This function can be called under rcu_read_lock(), given that the leaf
 * pointers lifetimes are correctly managed.
 *
 * Return: The pointer associated with this ID.
 */
void *idr_find(const struct idr *idr, unsigned long id)
{
        return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
}
EXPORT_SYMBOL_GPL(idr_find);

/**
 * 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 entry and @data.
 *
 * 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;
        int base = idr->idr_base;

        radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
                int ret;
                unsigned long id = iter.index + base;

                if (WARN_ON_ONCE(id > INT_MAX))
                        break;
                ret = fn(id, 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 an ID.
 *
 * 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;
        unsigned long base = idr->idr_base;
        unsigned long id = *nextid;

        id = (id < base) ? 0 : id - base;
        slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
        if (!slot)
                return NULL;
        id = iter.index + base;

        if (WARN_ON_ONCE(id > INT_MAX))
                return NULL;

        *nextid = id;
        return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next);

/**
 * idr_get_next_ul() - Find next populated entry.
 * @idr: IDR handle.
 * @nextid: Pointer to an ID.
 *
 * 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_ul(struct idr *idr, unsigned long *nextid)
{
        struct radix_tree_iter iter;
        void __rcu **slot;
        unsigned long base = idr->idr_base;
        unsigned long id = *nextid;

        id = (id < base) ? 0 : id - base;
        slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
        if (!slot)
                return NULL;

        *nextid = iter.index + base;
        return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next_ul);

/**
 * idr_replace() - replace pointer for given ID.
 * @idr: IDR handle.
 * @ptr: New pointer to associate with the ID.
 * @id: ID to change.
 *
 * 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: the old value on success.  %-ENOENT indicates that @id was not
 * found.  %-EINVAL indicates that @ptr was not valid.
 */
void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
{
        struct radix_tree_node *node;
        void __rcu **slot = NULL;
        void *entry;

        if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
                return ERR_PTR(-EINVAL);
        id -= idr->idr_base;

        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);

        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 - 1)

/**
 * 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;
                        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;
                        __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;

        xa_lock_irqsave(&ida->ida_rt, flags);
        ret = ida_get_new_above(ida, start, &id);
        if (!ret) {
                if (id > max) {
                        ida_remove(ida, id);
                        ret = -ENOSPC;
                } else {
                        ret = id;
                }
        }
        xa_unlock_irqrestore(&ida->ida_rt, 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);
        xa_lock_irqsave(&ida->ida_rt, flags);
        ida_remove(ida, id);
        xa_unlock_irqrestore(&ida->ida_rt, flags);
}
EXPORT_SYMBOL(ida_simple_remove);