On Wed, 16 Sep 2026 22:21:25 +0000 Bill Wendling <[email protected]> wrote:
> Converting some strlcat() call sites seq_buf need behavior seq_buf doesn't
> currently provide, either directly or without introducing subtle bugs:
>
> - seq_buf_strlen(): seq_buf_used() reports the full buffer size when the
> buffer is completely filled, even though seq_buf_str() then overwrites the
> final byte with a NUL terminator, leaving only size - 1 bytes of
> actual content. Callers that need the true length of the
> NUL-terminated string have to fall back to strlen(seq_buf_str(s)).
> seq_buf_strlen() mirrors seq_buf_str()'s NUL-termination logic but returns
> the resulting string's length directly.
>
> - seq_buf_init_append(): seq_buf_init() always clears the buffer it's given
> via seq_buf_clear(). Code migrating from strlcat(buf, ...), which
> appends to whatever @buf already contains, can't use seq_buf_init()
> without silently discarding that existing content. seq_buf_init_append()
> preserves it and positions the seq_buf to append after it.
>
> - seq_buf_puts_trunc(): seq_buf_puts() (like seq_buf_printf() and friends)
> writes nothing at all if the string doesn't fully fit, whereas strlcat()
> always copies as much of the source as there is room for. Converting a
> strlcat() call site that relied on that partial-copy behavior to
> plain seq_buf_puts() can silently drop content that used to survive
> truncated. seq_buf_puts_trunc() keeps the leading bytes of the string
> that fit.
>
> ...
>
> include/linux/seq_buf.h | 60 +++++++++++++++++++++++++++++++++++++++++
> lib/seq_buf.c | 35 ++++++++++++++++++++++++
> 2 files changed, 95 insertions(+)
This seems a lot of code for enabling some strlcat removals. How many
is "some"? If "3" then perhaps do something different at those
callsites?
Sashiko had a couple of comments:
https://sashiko.dev/#/patchset/[email protected]
Should these new functions be added to lib/tests/seq_buf_kunit.c?
