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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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74
lib/xarray.c
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@ -876,6 +876,80 @@ void xas_pause(struct xa_state *xas)
}
EXPORT_SYMBOL_GPL(xas_pause);
/*
* __xas_prev() - Find the previous entry in the XArray.
* @xas: XArray operation state.
*
* Helper function for xas_prev() which handles all the complex cases
* out of line.
*/
void *__xas_prev(struct xa_state *xas)
{
void *entry;
if (!xas_frozen(xas->xa_node))
xas->xa_index--;
if (xas_not_node(xas->xa_node))
return xas_load(xas);
if (xas->xa_offset != get_offset(xas->xa_index, xas->xa_node))
xas->xa_offset--;
while (xas->xa_offset == 255) {
xas->xa_offset = xas->xa_node->offset - 1;
xas->xa_node = xa_parent(xas->xa, xas->xa_node);
if (!xas->xa_node)
return set_bounds(xas);
}
for (;;) {
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);
}
}
EXPORT_SYMBOL_GPL(__xas_prev);
/*
* __xas_next() - Find the next entry in the XArray.
* @xas: XArray operation state.
*
* Helper function for xas_next() which handles all the complex cases
* out of line.
*/
void *__xas_next(struct xa_state *xas)
{
void *entry;
if (!xas_frozen(xas->xa_node))
xas->xa_index++;
if (xas_not_node(xas->xa_node))
return xas_load(xas);
if (xas->xa_offset != get_offset(xas->xa_index, xas->xa_node))
xas->xa_offset++;
while (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)
return set_bounds(xas);
}
for (;;) {
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);
}
}
EXPORT_SYMBOL_GPL(__xas_next);
/**
* xas_find() - Find the next present entry in the XArray.
* @xas: XArray operation state.