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Subject[PATCH v8 5/5] bitmap: extend comment to bitmap_print_to_buf
Date
From: Yury Norov <yury.norov@gmail.com>

Extend comment to new function to warn potential users about caveats.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
lib/bitmap.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 56bcffe2fa8c..608b79eabd43 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -545,6 +545,24 @@ EXPORT_SYMBOL(bitmap_print_to_pagebuf);
* mainly serves bin_attribute which doesn't work with exact one page, and it
* can break the size limit of converted decimal list and hexadecimal bitmask.
*
+ * WARNING!
+ *
+ * This function is not a replacement for sprintf() or bitmap_print_to_pagebuf().
+ * It is intended to workaround sysfs limitations discussed above and should be
+ * used carefully in general case for the following reasons:
+ * - Time complexity is O(nbits^2/count), comparing to O(nbits) for snprintf().
+ * - Memory complexity is O(nbits), comparing to O(1) for snprintf().
+ * - @off and @count are NOT offset and number of bits to print.
+ * - If printing part of bitmap as list, the resulting string is not a correct
+ * list representation of bitmap. Particularly, some bits within or out of
+ * related interval may be erroneously set or unset. The format of the string
+ * may be broken, so bitmap_parselist-like parser may fail parsing it.
+ * - If printing the whole bitmap as list by parts, user must ensure the order
+ * of calls of the function such that the offset is incremented linearly.
+ * - If printing the whole bitmap as list by parts, user must keep bitmap
+ * unchanged between the very first and very last call. Otherwise concatenated
+ * result may be incorrect, and format may be broken.
+ *
* Returns the number of characters actually printed to @buf
*/
int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
--
2.25.1
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