+ damon@lists.linux.dev

On Thu, 21 May 2026 06:33:22 -0700 Kees Cook [off-list ref] wrote:

Using the following Coccinelle script, convert struct kernel_param_ops
.get callbacks from "char *" to "struct seq_buf *" when the only write
to the buffer is via a final call of scnprintf(), snprintf(), sprintf(),
or sysfs_emit().

Since seq_buf_printf() will return -1 on overflow, and struct
kernel_param_ops .get callbacks are expected to truncate without error,
we must ignore the return value from seq_buf_print() and always return 0
(as the length is calculated in the common dispatcher code).

@@
identifier FN, BUF, KP;
expression FMT;
expression list ARGS;
@@
 int FN(
-               char *BUF
+               struct seq_buf *BUF
                , const struct kernel_param *KP)
 {
        ... when any
(
-       return scnprintf(BUF, PAGE_SIZE, FMT, ARGS);
|
-       return snprintf(BUF, PAGE_SIZE, FMT, ARGS);
|
-       return sprintf(BUF, FMT, ARGS);
|
-       return sysfs_emit(BUF, FMT, ARGS);
)
+       seq_buf_printf(BUF, FMT, ARGS);
+       return 0;
 }

No struct kernel_param_ops initializations need changing since
DEFINE_KERNEL_PARAM_OPS already routes the pointer to .get or .get_str
via _Generic based on the function signature, so converted callbacks
are automatically moved from the .get_str to the .get callback.

Signed-off-by: Kees Cook <kees@kernel.org>

[...]

 mm/damon/lru_sort.c                           | 14 +++---
 mm/damon/reclaim.c                            | 14 +++---
 mm/damon/stat.c                               | 10 ++--

For the above DAMON changes,

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]