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    Subject[PATCH v14 13/74] xarray: Add XArray iterators
    Date
    The xa_for_each iterator allows the user to efficiently walk a range
    of the array, executing the loop body once for each entry in that
    range that matches the filter. This commit also includes xa_find()
    and xa_find_above() which are helper functions for xa_for_each() but
    may also be useful in their own right.

    In the xas family of functions, we have xas_for_each(), xas_find(),
    xas_next_entry(), xas_for_each_tagged(), xas_find_tagged(),
    xas_next_tagged() and xas_pause().

    Signed-off-by: Matthew Wilcox <willy@infradead.org>
    ---
    include/linux/xarray.h | 169 +++++++++++++++++++++++++
    lib/test_xarray.c | 128 +++++++++++++++++++
    lib/xarray.c | 274 +++++++++++++++++++++++++++++++++++++++++
    3 files changed, 571 insertions(+)

    diff --git a/include/linux/xarray.h b/include/linux/xarray.h
    index 94b7f454a6a0..0790b3b098f0 100644
    --- a/include/linux/xarray.h
    +++ b/include/linux/xarray.h
    @@ -223,6 +223,10 @@ void *xa_cmpxchg(struct xarray *, unsigned long index,
    bool xa_get_tag(struct xarray *, unsigned long index, xa_tag_t);
    void xa_set_tag(struct xarray *, unsigned long index, xa_tag_t);
    void xa_clear_tag(struct xarray *, unsigned long index, xa_tag_t);
    +void *xa_find(struct xarray *xa, unsigned long *index,
    + unsigned long max, xa_tag_t) __attribute__((nonnull(2)));
    +void *xa_find_after(struct xarray *xa, unsigned long *index,
    + unsigned long max, xa_tag_t) __attribute__((nonnull(2)));

    /**
    * xa_init() - Initialise an empty XArray.
    @@ -307,6 +311,35 @@ static inline int xa_insert(struct xarray *xa, unsigned long index,
    return -EEXIST;
    }

    +/**
    + * xa_for_each() - Iterate over a portion of an XArray.
    + * @xa: XArray.
    + * @entry: Entry retrieved from array.
    + * @index: Index of @entry.
    + * @max: Maximum index to retrieve from array.
    + * @filter: Selection criterion.
    + *
    + * Initialise @index to the lowest index you want to retrieve from the
    + * array. During the iteration, @entry will have the value of the entry
    + * stored in @xa at @index. The iteration will skip all entries in the
    + * array which do not match @filter. You may modify @index during the
    + * iteration if you want to skip or reprocess indices. It is safe to modify
    + * the array during the iteration. At the end of the iteration, @entry will
    + * be set to NULL and @index will have a value less than or equal to max.
    + *
    + * xa_for_each() is O(n.log(n)) while xas_for_each() is O(n). You have
    + * to handle your own locking with xas_for_each(), and if you have to unlock
    + * after each iteration, it will also end up being O(n.log(n)). xa_for_each()
    + * will spin if it hits a retry entry; if you intend to see retry entries,
    + * you should use the xas_for_each() iterator instead. The xas_for_each()
    + * iterator will expand into more inline code than xa_for_each().
    + *
    + * Context: Any context. Takes and releases the RCU lock.
    + */
    +#define xa_for_each(xa, entry, index, max, filter) \
    + for (entry = xa_find(xa, &index, max, filter); entry; \
    + entry = xa_find_after(xa, &index, max, filter))
    +
    #define xa_trylock(xa) spin_trylock(&(xa)->xa_lock)
    #define xa_lock(xa) spin_lock(&(xa)->xa_lock)
    #define xa_unlock(xa) spin_unlock(&(xa)->xa_lock)
    @@ -726,13 +759,16 @@ static inline bool xas_retry(struct xa_state *xas, const void *entry)

    void *xas_load(struct xa_state *);
    void *xas_store(struct xa_state *, void *entry);
    +void *xas_find(struct xa_state *, unsigned long max);

    bool xas_get_tag(const struct xa_state *, xa_tag_t);
    void xas_set_tag(const struct xa_state *, xa_tag_t);
    void xas_clear_tag(const struct xa_state *, xa_tag_t);
    +void *xas_find_tagged(struct xa_state *, unsigned long max, xa_tag_t);
    void xas_init_tags(const struct xa_state *);

    bool xas_nomem(struct xa_state *, gfp_t);
    +void xas_pause(struct xa_state *);

    /**
    * xas_reload() - Refetch an entry from the xarray.
    @@ -805,6 +841,139 @@ static inline void xas_set_update(struct xa_state *xas, xa_update_node_t update)
    xas->xa_update = update;
    }

    +/* Skip over any of these entries when iterating */
    +static inline bool xa_iter_skip(const void *entry)
    +{
    + return unlikely(!entry ||
    + (xa_is_internal(entry) && entry < XA_RETRY_ENTRY));
    +}
    +
    +/**
    + * xas_next_entry() - Advance iterator to next present entry.
    + * @xas: XArray operation state.
    + * @max: Highest index to return.
    + *
    + * xas_next_entry() is an inline function to optimise xarray traversal for
    + * speed. It is equivalent to calling xas_find(), and will call xas_find()
    + * for all the hard cases.
    + *
    + * Return: The next present entry after the one currently referred to by @xas.
    + */
    +static inline void *xas_next_entry(struct xa_state *xas, unsigned long max)
    +{
    + struct xa_node *node = xas->xa_node;
    + void *entry;
    +
    + if (unlikely(xas_not_node(node) || node->shift))
    + return xas_find(xas, max);
    +
    + do {
    + if (unlikely(xas->xa_index >= max))
    + return xas_find(xas, max);
    + if (unlikely(xas->xa_offset == XA_CHUNK_MASK))
    + return xas_find(xas, max);
    + xas->xa_index++;
    + xas->xa_offset++;
    + entry = xa_entry(xas->xa, node, xas->xa_offset);
    + } while (xa_iter_skip(entry));
    +
    + return entry;
    +}
    +
    +/* Private */
    +static inline unsigned int xas_find_chunk(struct xa_state *xas, bool advance,
    + xa_tag_t tag)
    +{
    + unsigned long *addr = xas->xa_node->tags[(__force unsigned)tag];
    + unsigned int offset = xas->xa_offset;
    +
    + if (advance)
    + offset++;
    + if (XA_CHUNK_SIZE == BITS_PER_LONG) {
    + if (offset < XA_CHUNK_SIZE) {
    + unsigned long data = *addr & (~0UL << offset);
    + if (data)
    + return __ffs(data);
    + }
    + return XA_CHUNK_SIZE;
    + }
    +
    + return find_next_bit(addr, XA_CHUNK_SIZE, offset);
    +}
    +
    +/**
    + * xas_next_tagged() - Advance iterator to next tagged entry.
    + * @xas: XArray operation state.
    + * @max: Highest index to return.
    + * @tag: Tag to search for.
    + *
    + * xas_next_tagged() is an inline function to optimise xarray traversal for
    + * speed. It is equivalent to calling xas_find_tagged(), and will call
    + * xas_find_tagged() for all the hard cases.
    + *
    + * Return: The next tagged entry after the one currently referred to by @xas.
    + */
    +static inline void *xas_next_tagged(struct xa_state *xas, unsigned long max,
    + xa_tag_t tag)
    +{
    + struct xa_node *node = xas->xa_node;
    + unsigned int offset;
    +
    + if (unlikely(xas_not_node(node) || node->shift))
    + return xas_find_tagged(xas, max, tag);
    + offset = xas_find_chunk(xas, true, tag);
    + xas->xa_offset = offset;
    + xas->xa_index = (xas->xa_index & ~XA_CHUNK_MASK) + offset;
    + if (xas->xa_index > max)
    + return NULL;
    + if (offset == XA_CHUNK_SIZE)
    + return xas_find_tagged(xas, max, tag);
    + return xa_entry(xas->xa, node, offset);
    +}
    +
    +/*
    + * If iterating while holding a lock, drop the lock and reschedule
    + * every %XA_CHECK_SCHED loops.
    + */
    +enum {
    + XA_CHECK_SCHED = 4096,
    +};
    +
    +/**
    + * xas_for_each() - Iterate over a range of an XArray.
    + * @xas: XArray operation state.
    + * @entry: Entry retrieved from the array.
    + * @max: Maximum index to retrieve from array.
    + *
    + * The loop body will be executed for each entry present in the xarray
    + * between the current xas position and @max. @entry will be set to
    + * the entry retrieved from the xarray. It is safe to delete entries
    + * from the array in the loop body. You should hold either the RCU lock
    + * or the xa_lock while iterating. If you need to drop the lock, call
    + * xas_pause() first.
    + */
    +#define xas_for_each(xas, entry, max) \
    + for (entry = xas_find(xas, max); entry; \
    + entry = xas_next_entry(xas, max))
    +
    +/**
    + * xas_for_each_tagged() - Iterate over a range of an XArray.
    + * @xas: XArray operation state.
    + * @entry: Entry retrieved from the array.
    + * @max: Maximum index to retrieve from array.
    + * @tag: Tag to search for.
    + *
    + * The loop body will be executed for each tagged entry in the xarray
    + * between the current xas position and @max. @entry will be set to
    + * the entry retrieved from the xarray. It is safe to delete entries
    + * from the array in the loop body. You should hold either the RCU lock
    + * or the xa_lock while iterating. If you need to drop the lock, call
    + * xas_pause() first.
    + */
    +#define xas_for_each_tagged(xas, entry, max, tag) \
    + for (entry = xas_find_tagged(xas, max, tag); entry; \
    + entry = xas_next_tagged(xas, max, tag))
    +
    /* Internal functions, mostly shared between radix-tree.c, xarray.c and idr.c */
    void xas_destroy(struct xa_state *);

    diff --git a/lib/test_xarray.c b/lib/test_xarray.c
    index 35fca5e23cbc..a6a3705165ca 100644
    --- a/lib/test_xarray.c
    +++ b/lib/test_xarray.c
    @@ -73,6 +73,31 @@ static void check_xa_err(struct xarray *xa)
    // XA_BUG_ON(xa, xa_err(xa_store(xa, 0, xa_mk_internal(0), 0)) != -EINVAL);
    }

    +static void check_xas_retry(struct xarray *xa)
    +{
    + XA_STATE(xas, xa, 0);
    +
    + xa_store_value(xa, 0, GFP_KERNEL);
    + xa_store_value(xa, 1, GFP_KERNEL);
    +
    + XA_BUG_ON(xa, xas_find(&xas, ULONG_MAX) != xa_mk_value(0));
    + xa_erase_value(xa, 1);
    + XA_BUG_ON(xa, !xa_is_retry(xas_reload(&xas)));
    + XA_BUG_ON(xa, xas_retry(&xas, NULL));
    + XA_BUG_ON(xa, xas_retry(&xas, xa_mk_value(0)));
    + xas_reset(&xas);
    + XA_BUG_ON(xa, xas.xa_node != XAS_RESTART);
    + XA_BUG_ON(xa, xas_next_entry(&xas, ULONG_MAX) != xa_mk_value(0));
    + XA_BUG_ON(xa, xas.xa_node != NULL);
    +
    + XA_BUG_ON(xa, xa_store_value(xa, 1, GFP_KERNEL) != NULL);
    + XA_BUG_ON(xa, !xa_is_internal(xas_reload(&xas)));
    + xas.xa_node = XAS_RESTART;
    + XA_BUG_ON(xa, xas_next_entry(&xas, ULONG_MAX) != xa_mk_value(0));
    + xa_erase_value(xa, 0);
    + xa_erase_value(xa, 1);
    +}
    +
    static void check_xa_load(struct xarray *xa)
    {
    unsigned long i, j;
    @@ -200,6 +225,37 @@ static void check_cmpxchg(struct xarray *xa)
    XA_BUG_ON(xa, !xa_empty(xa));
    }

    +static void check_xas_erase(struct xarray *xa)
    +{
    + XA_STATE(xas, xa, 0);
    + void *entry;
    + unsigned long i, j;
    +
    + for (i = 0; i < 200; i++) {
    + for (j = i; j < 2 * i + 17; j++) {
    + xas_set(&xas, j);
    + do {
    + xas_store(&xas, xa_mk_value(j));
    + } while (xas_nomem(&xas, GFP_KERNEL));
    + }
    +
    + xas_set(&xas, ULONG_MAX);
    + do {
    + xas_store(&xas, xa_mk_value(0));
    + } while (xas_nomem(&xas, GFP_KERNEL));
    + xas_store(&xas, NULL);
    +
    + xas_set(&xas, 0);
    + j = i;
    + xas_for_each(&xas, entry, ULONG_MAX) {
    + XA_BUG_ON(xa, entry != xa_mk_value(j));
    + xas_store(&xas, NULL);
    + j++;
    + }
    + XA_BUG_ON(xa, !xa_empty(xa));
    + }
    +}
    +
    static void check_multi_store(struct xarray *xa)
    {
    unsigned long i, j, k;
    @@ -259,16 +315,88 @@ static void check_multi_store(struct xarray *xa)
    }
    }

    +static void check_multi_find(struct xarray *xa)
    +{
    + unsigned long index;
    +
    + xa_store_order(xa, 12, 2, xa_mk_value(12), GFP_KERNEL);
    + XA_BUG_ON(xa, xa_store_value(xa, 16, GFP_KERNEL) != NULL);
    +
    + index = 0;
    + XA_BUG_ON(xa, xa_find(xa, &index, ULONG_MAX, XA_PRESENT) !=
    + xa_mk_value(12));
    + XA_BUG_ON(xa, index != 12);
    + index = 13;
    + XA_BUG_ON(xa, xa_find(xa, &index, ULONG_MAX, XA_PRESENT) !=
    + xa_mk_value(12));
    + XA_BUG_ON(xa, (index < 12) || (index >= 16));
    + XA_BUG_ON(xa, xa_find_after(xa, &index, ULONG_MAX, XA_PRESENT) !=
    + xa_mk_value(16));
    + XA_BUG_ON(xa, index != 16);
    +
    + xa_erase_value(xa, 12);
    + xa_erase_value(xa, 16);
    + XA_BUG_ON(xa, !xa_empty(xa));
    +}
    +
    +static void check_find(struct xarray *xa)
    +{
    + unsigned long i, j, k;
    +
    + XA_BUG_ON(xa, !xa_empty(xa));
    +
    + for (i = 0; i < 100; i++) {
    + XA_BUG_ON(xa, xa_store_value(xa, i, GFP_KERNEL) != NULL);
    + xa_set_tag(xa, i, XA_TAG_0);
    + for (j = 0; j < i; j++) {
    + XA_BUG_ON(xa, xa_store_value(xa, j, GFP_KERNEL) !=
    + NULL);
    + xa_set_tag(xa, j, XA_TAG_0);
    + for (k = 0; k < 100; k++) {
    + unsigned long index = k;
    + void *entry = xa_find(xa, &index, ULONG_MAX,
    + XA_PRESENT);
    + if (k <= j)
    + XA_BUG_ON(xa, index != j);
    + else if (k <= i)
    + XA_BUG_ON(xa, index != i);
    + else
    + XA_BUG_ON(xa, entry != NULL);
    +
    + index = k;
    + entry = xa_find(xa, &index, ULONG_MAX,
    + XA_TAG_0);
    + if (k <= j)
    + XA_BUG_ON(xa, index != j);
    + else if (k <= i)
    + XA_BUG_ON(xa, index != i);
    + else
    + XA_BUG_ON(xa, entry != NULL);
    + }
    + xa_erase_value(xa, j);
    + XA_BUG_ON(xa, xa_get_tag(xa, j, XA_TAG_0));
    + XA_BUG_ON(xa, !xa_get_tag(xa, i, XA_TAG_0));
    + }
    + xa_erase_value(xa, i);
    + XA_BUG_ON(xa, xa_get_tag(xa, i, XA_TAG_0));
    + }
    + XA_BUG_ON(xa, !xa_empty(xa));
    + check_multi_find(xa);
    +}
    +
    static int xarray_checks(void)
    {
    DEFINE_XARRAY(array);

    check_xa_err(&array);
    + check_xas_retry(&array);
    check_xa_load(&array);
    check_xa_tag(&array);
    check_xa_shrink(&array);
    + check_xas_erase(&array);
    check_cmpxchg(&array);
    check_multi_store(&array);
    + check_find(&array);

    printk("XArray: %u of %u tests passed\n", tests_passed, tests_run);
    return (tests_run != tests_passed) ? 0 : -EINVAL;
    diff --git a/lib/xarray.c b/lib/xarray.c
    index 1a3a256cbb37..8756ca22363e 100644
    --- a/lib/xarray.c
    +++ b/lib/xarray.c
    @@ -103,6 +103,11 @@ static unsigned int get_offset(unsigned long index, struct xa_node *node)
    return (index >> node->shift) & XA_CHUNK_MASK;
    }

    +static void xas_set_offset(struct xa_state *xas)
    +{
    + xas->xa_offset = get_offset(xas->xa_index, xas->xa_node);
    +}
    +
    /* move the index either forwards (find) or backwards (sibling slot) */
    static void xas_move_index(struct xa_state *xas, unsigned long offset)
    {
    @@ -111,6 +116,12 @@ static void xas_move_index(struct xa_state *xas, unsigned long offset)
    xas->xa_index += offset << shift;
    }

    +static void xas_advance(struct xa_state *xas)
    +{
    + xas->xa_offset++;
    + xas_move_index(xas, xas->xa_offset);
    +}
    +
    static void *set_bounds(struct xa_state *xas)
    {
    xas->xa_node = XAS_BOUNDS;
    @@ -816,6 +827,191 @@ void xas_init_tags(const struct xa_state *xas)
    }
    EXPORT_SYMBOL_GPL(xas_init_tags);

    +/**
    + * xas_pause() - Pause a walk to drop a lock.
    + * @xas: XArray operation state.
    + *
    + * Some users need to pause a walk and drop the lock they're holding in
    + * order to yield to a higher priority thread or carry out an operation
    + * on an entry. Those users should call this function before they drop
    + * the lock. It resets the @xas to be suitable for the next iteration
    + * of the loop after the user has reacquired the lock. If most entries
    + * found during a walk require you to call xas_pause(), the xa_for_each()
    + * iterator may be more appropriate.
    + *
    + * Note that xas_pause() only works for forward iteration. If a user needs
    + * to pause a reverse iteration, we will need a xas_pause_rev().
    + */
    +void xas_pause(struct xa_state *xas)
    +{
    + struct xa_node *node = xas->xa_node;
    +
    + if (xas_invalid(xas))
    + return;
    +
    + if (node) {
    + unsigned int offset = xas->xa_offset;
    + while (++offset < XA_CHUNK_SIZE) {
    + if (!xa_is_sibling(xa_entry(xas->xa, node, offset)))
    + break;
    + }
    + xas->xa_index += (offset - xas->xa_offset) << node->shift;
    + } else {
    + xas->xa_index++;
    + }
    + xas->xa_node = XAS_RESTART;
    +}
    +EXPORT_SYMBOL_GPL(xas_pause);
    +
    +/**
    + * xas_find() - Find the next present entry in the XArray.
    + * @xas: XArray operation state.
    + * @max: Highest index to return.
    + *
    + * If the xas has not yet been walked to an entry, return the entry
    + * which has an index >= xas.xa_index. If it has been walked, the entry
    + * currently being pointed at has been processed, and so we move to the
    + * next entry.
    + *
    + * If no entry is found and the array is smaller than @max, the iterator
    + * is set to the smallest index not yet in the array. This allows @xas
    + * to be immediately passed to xas_store().
    + *
    + * Return: The entry, if found, otherwise NULL.
    + */
    +void *xas_find(struct xa_state *xas, unsigned long max)
    +{
    + void *entry;
    +
    + if (xas_error(xas))
    + return NULL;
    +
    + if (!xas->xa_node) {
    + xas->xa_index = 1;
    + return set_bounds(xas);
    + } else if (xas_top(xas->xa_node)) {
    + entry = xas_load(xas);
    + if (entry || xas_not_node(xas->xa_node))
    + return entry;
    + }
    +
    + xas_advance(xas);
    +
    + while (xas->xa_node && (xas->xa_index <= max)) {
    + if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
    + xas->xa_offset = xas->xa_node->offset + 1;
    + xas->xa_node = xa_parent(xas->xa, xas->xa_node);
    + continue;
    + }
    +
    + entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
    + if (xa_is_node(entry)) {
    + xas->xa_node = xa_to_node(entry);
    + xas->xa_offset = 0;
    + continue;
    + }
    + if (!xa_iter_skip(entry))
    + return entry;
    +
    + xas_advance(xas);
    + }
    +
    + if (!xas->xa_node)
    + xas->xa_node = XAS_BOUNDS;
    + return NULL;
    +}
    +EXPORT_SYMBOL_GPL(xas_find);
    +
    +/**
    + * xas_find_tagged() - Find the next tagged entry in the XArray.
    + * @xas: XArray operation state.
    + * @max: Highest index to return.
    + * @tag: Tag number to search for.
    + *
    + * If the xas has not yet been walked to an entry, return the tagged entry
    + * which has an index >= xas.xa_index. If it has been walked, the entry
    + * currently being pointed at has been processed, and so we move to the
    + * next tagged entry.
    + *
    + * If no tagged entry is found and the array is smaller than @max, @xas is
    + * set to the bounds state and xas->xa_index is set to the smallest index
    + * not yet in the array. This allows @xas to be immediately passed to
    + * xas_store().
    + *
    + * Return: The entry, if found, otherwise %NULL.
    + */
    +void *xas_find_tagged(struct xa_state *xas, unsigned long max, xa_tag_t tag)
    +{
    + bool advance = true;
    + unsigned int offset;
    + void *entry;
    +
    + if (xas_error(xas))
    + return NULL;
    +
    + if (!xas->xa_node) {
    + xas->xa_index = 1;
    + goto out;
    + } else if (xas_top(xas->xa_node)) {
    + advance = false;
    + entry = xa_head(xas->xa);
    + if (xas->xa_index > max_index(entry))
    + goto out;
    + if (!xa_is_node(entry)) {
    + if (xa_tagged(xas->xa, tag)) {
    + xas->xa_node = NULL;
    + return entry;
    + }
    + xas->xa_index = 1;
    + goto out;
    + }
    + xas->xa_node = xa_to_node(entry);
    + xas->xa_offset = xas->xa_index >> xas->xa_node->shift;
    + }
    +
    + while (xas->xa_index <= max) {
    + if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
    + xas->xa_offset = xas->xa_node->offset + 1;
    + xas->xa_node = xa_parent(xas->xa, xas->xa_node);
    + if (!xas->xa_node)
    + break;
    + advance = false;
    + continue;
    + }
    +
    + if (!advance) {
    + entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
    + if (xa_is_sibling(entry)) {
    + xas->xa_offset = xa_to_sibling(entry);
    + xas_move_index(xas, xas->xa_offset);
    + }
    + }
    +
    + offset = xas_find_chunk(xas, advance, tag);
    + if (offset > xas->xa_offset) {
    + advance = false;
    + xas_move_index(xas, offset);
    + xas->xa_offset = offset;
    + if (offset == XA_CHUNK_SIZE)
    + continue;
    + if (xas->xa_index > max)
    + break;
    + }
    +
    + entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
    + if (!xa_is_node(entry))
    + return entry;
    + xas->xa_node = xa_to_node(entry);
    + xas_set_offset(xas);
    + }
    +
    + out:
    + if (!xas->xa_node)
    + xas->xa_node = XAS_BOUNDS;
    + return NULL;
    +}
    +EXPORT_SYMBOL_GPL(xas_find_tagged);
    +
    /**
    * xa_init_flags() - Initialise an empty XArray with flags.
    * @xa: XArray.
    @@ -1139,6 +1335,84 @@ void xa_clear_tag(struct xarray *xa, unsigned long index, xa_tag_t tag)
    }
    EXPORT_SYMBOL(xa_clear_tag);

    +/**
    + * xa_find() - Search the XArray for an entry.
    + * @xa: XArray.
    + * @indexp: Pointer to an index.
    + * @max: Maximum index to search to.
    + * @filter: Selection criterion.
    + *
    + * Finds the entry in @xa which matches the @filter, and has the lowest
    + * index that is at least @indexp and no more than @max.
    + * If an entry is found, @indexp is updated to be the index of the entry.
    + * This function is protected by the RCU read lock, so it may not find
    + * entries which are being simultaneously added. It will not return an
    + * %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
    + *
    + * Context: Any context. Takes and releases the RCU lock.
    + * Return: The entry, if found, otherwise NULL.
    + */
    +void *xa_find(struct xarray *xa, unsigned long *indexp,
    + unsigned long max, xa_tag_t filter)
    +{
    + XA_STATE(xas, xa, *indexp);
    + void *entry;
    +
    + rcu_read_lock();
    + do {
    + if ((__force unsigned int)filter < XA_MAX_TAGS)
    + entry = xas_find_tagged(&xas, max, filter);
    + else
    + entry = xas_find(&xas, max);
    + } while (xas_retry(&xas, entry));
    + rcu_read_unlock();
    +
    + if (entry)
    + *indexp = xas.xa_index;
    + return entry;
    +}
    +EXPORT_SYMBOL(xa_find);
    +
    +/**
    + * xa_find_after() - Search the XArray for a present entry.
    + * @xa: XArray.
    + * @indexp: Pointer to an index.
    + * @max: Maximum index to search to.
    + * @filter: Selection criterion.
    + *
    + * Finds the entry in @xa which matches the @filter and has the lowest
    + * index that is above @indexp and no more than @max.
    + * If an entry is found, @indexp is updated to be the index of the entry.
    + * This function is protected by the RCU read lock, so it may miss entries
    + * which are being simultaneously added. It will not return an
    + * %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
    + *
    + * Context: Any context. Takes and releases the RCU lock.
    + * Return: The pointer, if found, otherwise NULL.
    + */
    +void *xa_find_after(struct xarray *xa, unsigned long *indexp,
    + unsigned long max, xa_tag_t filter)
    +{
    + XA_STATE(xas, xa, *indexp + 1);
    + void *entry;
    +
    + rcu_read_lock();
    + do {
    + if ((__force unsigned int)filter < XA_MAX_TAGS)
    + entry = xas_find_tagged(&xas, max, filter);
    + else
    + entry = xas_find(&xas, max);
    + if (*indexp >= xas.xa_index)
    + entry = xas_next_entry(&xas, max);
    + } while (xas_retry(&xas, entry));
    + rcu_read_unlock();
    +
    + if (entry)
    + *indexp = xas.xa_index;
    + return entry;
    +}
    +EXPORT_SYMBOL(xa_find_after);
    +
    #ifdef XA_DEBUG
    void xa_dump_node(const struct xa_node *node)
    {
    --
    2.17.1
    \
     
     \ /
      Last update: 2018-06-17 04:15    [W:2.620 / U:0.012 seconds]
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