[v2,2/2] iio: buffer: document known issue
Commit Message
Add documentation explaining why the code which scans all available scan
masks is checking only a single long worth of bits even though the code
was intended to be supporting masks wider than single long.
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
drivers/iio/industrialio-buffer.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
@@ -413,6 +413,22 @@ static const unsigned long *iio_scan_mask_match(const unsigned long *av_masks,
{
if (bitmap_empty(mask, masklength))
return NULL;
+ /*
+ * The condition here do not handle multi-long masks correctly.
+ * It only checks the first long to be zero, and will use such mask
+ * as a terminator even if there was bits set after the first long.
+ *
+ * Correct check would require using:
+ * while (!bitmap_empty(av_masks, masklength))
+ * instead. This is potentially hazardous because the
+ * avaliable_scan_masks is a zero terminated array of longs - and
+ * using the proper bitmap_empty() check for multi-long wide masks
+ * would require the array to be terminated with multiple zero longs -
+ * which is not such an usual pattern.
+ *
+ * As writing of this no multi-long wide masks were found in-tree, so
+ * the simple while (*av_masks) check is working.
+ */
while (*av_masks) {
if (strict) {
if (bitmap_equal(mask, av_masks, masklength))