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xarray: Step through an XArray

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The xas_next and xas_prev functions move the xas index by one position,
and adjust the rest of the iterator state to match it.  This is more
efficient than calling xas_set() as it keeps the iterator at the leaves
of the tree instead of walking the iterator from the root each time.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
This commit is contained in:
Matthew Wilcox 2017-12-01 00:06:52 -05:00
parent 687149fca1
commit 64d3e9a9e0
3 changed files with 256 additions and 0 deletions
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67
include/linux/xarray.h
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@ -828,6 +828,12 @@ static inline bool xas_not_node(struct xa_node *node)
return ((unsigned long)node & 3) || !node;
}
/* True if the node represents RESTART or an error */
static inline bool xas_frozen(struct xa_node *node)
{
return (unsigned long)node & 2;
}
/* True if the node represents head-of-tree, RESTART or BOUNDS */
static inline bool xas_top(struct xa_node *node)
{
@ -1082,4 +1088,65 @@ enum {
for (entry = xas_find_marked(xas, max, mark); entry; \
entry = xas_next_marked(xas, max, mark))
void *__xas_next(struct xa_state *);
void *__xas_prev(struct xa_state *);
/**
* xas_prev() - Move iterator to previous index.
* @xas: XArray operation state.
*
* If the @xas was in an error state, it will remain in an error state
* and this function will return %NULL. If the @xas has never been walked,
* it will have the effect of calling xas_load(). Otherwise one will be
* subtracted from the index and the state will be walked to the correct
* location in the array for the next operation.
*
* If the iterator was referencing index 0, this function wraps
* around to %ULONG_MAX.
*
* Return: The entry at the new index. This may be %NULL or an internal
* entry.
*/
static inline void *xas_prev(struct xa_state *xas)
{
struct xa_node *node = xas->xa_node;
if (unlikely(xas_not_node(node) || node->shift ||
xas->xa_offset == 0))
return __xas_prev(xas);
xas->xa_index--;
xas->xa_offset--;
return xa_entry(xas->xa, node, xas->xa_offset);
}
/**
* xas_next() - Move state to next index.
* @xas: XArray operation state.
*
* If the @xas was in an error state, it will remain in an error state
* and this function will return %NULL. If the @xas has never been walked,
* it will have the effect of calling xas_load(). Otherwise one will be
* added to the index and the state will be walked to the correct
* location in the array for the next operation.
*
* If the iterator was referencing index %ULONG_MAX, this function wraps
* around to 0.
*
* Return: The entry at the new index. This may be %NULL or an internal
* entry.
*/
static inline void *xas_next(struct xa_state *xas)
{
struct xa_node *node = xas->xa_node;
if (unlikely(xas_not_node(node) || node->shift ||
xas->xa_offset == XA_CHUNK_MASK))
return __xas_next(xas);
xas->xa_index++;
xas->xa_offset++;
return xa_entry(xas->xa, node, xas->xa_offset);
}
#endif /* _LINUX_XARRAY_H */