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    Subject[PATCH v9 19/61] xarray: Add xa_extract
    Date
    From: Matthew Wilcox <mawilcox@microsoft.com>

    This function combines the functionality of radix_tree_gang_lookup() and
    radix_tree_gang_lookup_tagged(). It extracts entries matching the
    specified filter into a normal array.

    Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
    ---
    include/linux/xarray.h | 2 ++
    lib/xarray.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 82 insertions(+)

    diff --git a/include/linux/xarray.h b/include/linux/xarray.h
    index cf7966bfdd3e..85dd909586f0 100644
    --- a/include/linux/xarray.h
    +++ b/include/linux/xarray.h
    @@ -227,6 +227,8 @@ 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)));
    +unsigned int xa_extract(struct xarray *, void **dst, unsigned long start,
    + unsigned long max, unsigned int n, xa_tag_t);

    /**
    * xa_init() - Initialise an empty XArray.
    diff --git a/lib/xarray.c b/lib/xarray.c
    index 267510e98a57..124bbfec66ae 100644
    --- a/lib/xarray.c
    +++ b/lib/xarray.c
    @@ -1388,6 +1388,86 @@ void *xa_find_after(struct xarray *xa, unsigned long *indexp,
    }
    EXPORT_SYMBOL(xa_find_after);

    +static unsigned int xas_extract_present(struct xa_state *xas, void **dst,
    + unsigned long max, unsigned int n)
    +{
    + void *entry;
    + unsigned int i = 0;
    +
    + rcu_read_lock();
    + xas_for_each(xas, entry, max) {
    + if (xas_retry(xas, entry))
    + continue;
    + dst[i++] = entry;
    + if (i == n)
    + break;
    + }
    + rcu_read_unlock();
    +
    + return i;
    +}
    +
    +static unsigned int xas_extract_tag(struct xa_state *xas, void **dst,
    + unsigned long max, unsigned int n, xa_tag_t tag)
    +{
    + void *entry;
    + unsigned int i = 0;
    +
    + rcu_read_lock();
    + xas_for_each_tag(xas, entry, max, tag) {
    + if (xas_retry(xas, entry))
    + continue;
    + dst[i++] = entry;
    + if (i == n)
    + break;
    + }
    + rcu_read_unlock();
    +
    + return i;
    +}
    +
    +/**
    + * xa_extract() - Copy selected entries from the XArray into a normal array.
    + * @xa: The source XArray to copy from.
    + * @dst: The buffer to copy entries into.
    + * @start: The first index in the XArray eligible to be selected.
    + * @max: The last index in the XArray eligible to be selected.
    + * @n: The maximum number of entries to copy.
    + * @filter: Selection criterion.
    + *
    + * Copies up to @n entries that match @filter from the XArray. The
    + * copied entries will have indices between @start and @max, inclusive.
    + *
    + * The @filter may be an XArray tag value, in which case entries which are
    + * tagged with that tag will be copied. It may also be %XA_PRESENT, in
    + * which case non-NULL entries will be copied.
    + *
    + * The entries returned may not represent a snapshot of the XArray at a
    + * moment in time. For example, if another thread stores to index 5, then
    + * index 10, calling xa_extract() may return the old contents of index 5
    + * and the new contents of index 10. Indices not modified while this
    + * function is running will not be skipped.
    + *
    + * If you need stronger guarantees, holding the xa_lock across calls to this
    + * function will prevent concurrent modification.
    + *
    + * Context: Any context. Takes and releases the RCU lock.
    + * Return: The number of entries copied.
    + */
    +unsigned int xa_extract(struct xarray *xa, void **dst, unsigned long start,
    + unsigned long max, unsigned int n, xa_tag_t filter)
    +{
    + XA_STATE(xas, xa, start);
    +
    + if (!n)
    + return 0;
    +
    + if ((__force unsigned int)filter < XA_MAX_TAGS)
    + return xas_extract_tag(&xas, dst, max, n, filter);
    + return xas_extract_present(&xas, dst, max, n);
    +}
    +EXPORT_SYMBOL(xa_extract);
    +
    #ifdef XA_DEBUG
    void xa_dump_node(const struct xa_node *node)
    {
    --
    2.16.1
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