Re: [PATCH v2 1/3] Doc: deprecated.rst: add strlcat()

[Heiko Carstens <hca@linux.ibm.com>]

On Thu, May 14, 2026 at 09:31:46AM -0700, Kees Cook wrote:
> On Thu, May 14, 2026 at 06:26:53PM +0200, Manuel Ebner wrote:
> > add strlcat and alternatives
> > 
> > Signed-off-by: Manuel Ebner <manuelebner@mailbox.org>
> > ---
> >  Documentation/process/deprecated.rst | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> > index fed56864d036..06e802f4bbfd 100644
> > --- a/Documentation/process/deprecated.rst
> > +++ b/Documentation/process/deprecated.rst
> > @@ -153,6 +153,13 @@ used, and the destinations should be marked with the `__nonstring
> >  attribute to avoid future compiler warnings. For cases still needing
> >  NUL-padding, strtomem_pad() can be used.
> >  
> > +strlcat()
> > +---------
> > +strlcat() must re-scan the destination string from the beginning on each
> > +call (O(n^2) behavior). Alternatives are seq_buf_puts() and seq_buf_printf().
> > +snprintf(), scnprintf() and sysfs_emit() are possible aswell, but the adoption
> > +of the arguments needs to be taken care off.
> > +
> 
> How about just:
> 
> strlcat() must re-scan the destination string from the beginning on each
> call (O(n^2) behavior). Use the seq_buf API or similar instead.

seq_buf API for appending something to e.g. boot_command_line seems to be odd,
since boot_command_line is usually "just there" (depending on architecture and
boot loader).

So if I would remove strlcat() from appending something to boot_command_line I
would end up open-coding strlcat(), including the chance for the usual
off-by-one bugs. Looks like this would be true for nearly all architectures.

Is performance really the only reason to deprecate strlcat()? This seems to be
a bit questionable to me.