Re: ssize_t: was: Re: [PATCH] of: Add printf '%pOFm' for generating modalias

[Rob Herring <robh@kernel.org>]

On Wed, Dec 18, 2024 at 5:35 AM Petr Mladek <pmladek@suse.com> wrote:
>
> On Tue 2024-12-17 12:37:09, Rob Herring (Arm) wrote:
> > The callers for of_modalias() generally need the module alias as part of
> > some larger string. That results in some error prone manipulation of the
> > buffer prepend/append the module alias string. In fact,
> > of_device_uevent_modalias() has several issues. First, it's off by one
> > too few characters in utilization of the full buffer. Second, the error
> > paths leave OF_MODALIAS with a truncated value when in the end nothing
> > should be added to the buffer. It is also fragile because it needs
> > internal details of struct kobj_uevent_env. add_uevent_var() really
> > wants to write the env variable and value in one shot which would need
> > either a temporary buffer for value or a format specifier.
> >
> > Fix these issues by adding a new printf format specifier, "%pOFm". With
> > the format specifier in place, simplify all the callers of
> > of_modalias(). of_modalias() can also be simplified with vsprintf()
> > being the only caller as it avoids the error conditions.
> >
> > --- a/drivers/of/module.c
> > +++ b/drivers/of/module.c
> > @@ -8,21 +8,14 @@
> >  #include <linux/slab.h>
> >  #include <linux/string.h>
> >
> > -ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
> > +/* Do not use directly, use %pOFm format specifier instead */
> > +size_t of_modalias(const struct device_node *np, char *str, size_t len)
>
> We should keep ssize_t.

My intent was to align of_modalias() with snprintf()...

> "end - buf" passed from device_node_string() in vprintf.c might be
> negative. The "buf" pointer is used to count the number of characters
> which might be written when the buffer is big enough.

Isn't Rasmus' suggestion sufficient?:

buf += of_modalias(dn, buf, buf < end ? end - buf : 0)

Rob