diff options
Diffstat (limited to 'lib/idr.c')
| -rw-r--r-- | lib/idr.c | 581 |
1 files changed, 581 insertions, 0 deletions
diff --git a/lib/idr.c b/lib/idr.c new file mode 100644 index 000000000..6ff3b1c36 --- /dev/null +++ b/lib/idr.c @@ -0,0 +1,581 @@ +#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_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; + void *entry = NULL; + unsigned long base = idr->idr_base; + unsigned long id = *nextid; + + id = (id < base) ? 0 : id - base; + radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, id) { + entry = rcu_dereference_raw(*slot); + if (!entry) + continue; + if (!radix_tree_deref_retry(entry)) + break; + if (slot != (void *)&idr->idr_rt.rnode && + entry != (void *)RADIX_TREE_INTERNAL_NODE) + break; + slot = radix_tree_iter_retry(&iter); + } + if (!slot) + return NULL; + + *nextid = iter.index + base; + return entry; +} +EXPORT_SYMBOL(idr_get_next_ul); + +/** + * 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) +{ + unsigned long id = *nextid; + void *entry = idr_get_next_ul(idr, &id); + + if (WARN_ON_ONCE(id > INT_MAX)) + return NULL; + *nextid = id; + return entry; +} +EXPORT_SYMBOL(idr_get_next); + +/** + * 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_alloc(), ida_alloc_min(), ida_alloc_max() or ida_alloc_range(). + * To free an ID, call ida_free(). + * + * 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) + +static int ida_get_new_above(struct ida *ida, int start) +{ + 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); + return new + ebit - + RADIX_TREE_EXCEPTIONAL_SHIFT; + } + 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); + return new; + } + bitmap = this_cpu_xchg(ida_bitmap, NULL); + if (!bitmap) + return -EAGAIN; + __set_bit(bit, bitmap->bitmap); + radix_tree_iter_replace(root, &iter, slot, bitmap); + } + + return new; + } +} + +static 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_free called for id=%d which is not allocated.\n", id); +} + +/** + * ida_destroy() - Free all IDs. + * @ida: IDA handle. + * + * Calling this function frees all IDs and releases all resources used + * by an IDA. When this call returns, the IDA is empty and can be reused + * or freed. If the IDA is already empty, there is no need to call this + * function. + * + * Context: Any context. + */ +void ida_destroy(struct ida *ida) +{ + unsigned long flags; + struct radix_tree_iter iter; + void __rcu **slot; + + xa_lock_irqsave(&ida->ida_rt, flags); + 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); + } + xa_unlock_irqrestore(&ida->ida_rt, flags); +} +EXPORT_SYMBOL(ida_destroy); + +/** + * ida_alloc_range() - Allocate an unused ID. + * @ida: IDA handle. + * @min: Lowest ID to allocate. + * @max: Highest ID to allocate. + * @gfp: Memory allocation flags. + * + * Allocate an ID between @min and @max, inclusive. The allocated ID will + * not exceed %INT_MAX, even if @max is larger. + * + * Context: Any context. + * Return: The allocated ID, or %-ENOMEM if memory could not be allocated, + * or %-ENOSPC if there are no free IDs. + */ +int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max, + gfp_t gfp) +{ + int id = 0; + unsigned long flags; + + if ((int)min < 0) + return -ENOSPC; + + if ((int)max < 0) + max = INT_MAX; + +again: + xa_lock_irqsave(&ida->ida_rt, flags); + id = ida_get_new_above(ida, min); + if (id > (int)max) { + ida_remove(ida, id); + id = -ENOSPC; + } + xa_unlock_irqrestore(&ida->ida_rt, flags); + + if (unlikely(id == -EAGAIN)) { + if (!ida_pre_get(ida, gfp)) + return -ENOMEM; + goto again; + } + + return id; +} +EXPORT_SYMBOL(ida_alloc_range); + +/** + * ida_free() - Release an allocated ID. + * @ida: IDA handle. + * @id: Previously allocated ID. + * + * Context: Any context. + */ +void ida_free(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_free); |