linux-kernel - Re: [PATCH v4 10/11] lib/vsprintf: Add %pfw conversion specifier for printing fwnode names

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Message-ID: <20190903130607.cf2qv3s3evobbd5g@pathway.suse.cz>
Date:   Tue, 3 Sep 2019 15:06:07 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        devicetree@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 10/11] lib/vsprintf: Add %pfw conversion specifier for
 printing fwnode names

On Mon 2019-09-02 11:32:39, Sakari Ailus wrote:
> Add support for %pfw conversion specifier (with "f" and "P" modifiers) to
> support printing full path of the node, including its name ("f") and only
> the node's name ("P") in the printk family of functions. The two flags
> have equivalent functionality to existing %pOF with the same two modifiers
> ("f" and "P") on OF based systems. The ability to do the same on ACPI
> based systems is added by this patch.
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index 922a29eb70e6c..abba210f67567 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -418,6 +418,30 @@ Examples::
>  
>  Passed by reference.
>  
> +Fwnode handles
> +--------------
> +
> +::
> +
> +	%pfw[fP]
> +
> +For printing information on fwnode handles. The default is to print the full
> +node name, including the path. The modifiers are functionally equivalent to
> +%pOF above.
> +
> +	- f - full name of the node, including the path
> +	- P - the name of the node including an address (if there is one)
> +
> +Examples (ACPI):

s/:/::/ for the .rst formar.

> +
> +	%pfwf	\_SB.PCI0.CIO2.port@...ndpoint@0	- Full node name
> +	%pfwP	endpoint@0				- Node name
> +
> +Examples (OF):

Same here.

> +
> +	%pfwf	/ocp@...00000/i2c@...72000/camera@...port/endpoint - Full name
> +	%pfwP	endpoint				- Node name
> +
>  Time and date (struct rtc_time)
>  -------------------------------
>  
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 4ad9332d54ba6..b9b4c835db063 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1981,6 +1981,36 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
>  	return widen_string(buf, buf - buf_start, end, spec);
>  }
>  
> +static noinline_for_stack
> +char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
> +		    struct printf_spec spec, const char *fmt)
> +{
> +	struct printf_spec str_spec = spec;
> +	char *buf_start = buf;
> +
> +	str_spec.field_width = -1;
> +
> +	if (*fmt != 'w')
> +		return error_string(buf, end, "(%pfw?)", spec);

This means that only "%pfw" will dereference the pointer by
fwnode_full_name_string() or fwnode_get_name(). All the other
eventual misuses of the obsolete %pf format will result in this
error message.

OK, it is hard to imagine using "%pf" to get symbol name and always add
'w' suffix. Therefore it looks that reusing the obsolete %pf format
modifier is pretty safe after all.


> +	if (check_pointer(&buf, end, fwnode, spec))
> +		return buf;
> +
> +	fmt++;
> +
> +	switch (*fmt) {
> +	case 'f':	/* full_name */
> +	default:

Using default: in the middle of switch might cause a lot of confusion.
Please, make it the last label.


> +		buf = fwnode_full_name_string(fwnode, buf, end);
> +		break;
> +	case 'P':	/* name */
> +		buf = string(buf, end, fwnode_get_name(fwnode), str_spec);
> +		break;
> +	}
> +
> +	return widen_string(buf, buf - buf_start, end, spec);
> +}
> +
>  /*
>   * Show a '%p' thing.  A kernel extension is that the '%p' is followed
>   * by an extra set of alphanumeric characters that are extended format
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index a60c241112cd4..8df50911ff4e9 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -5995,7 +5995,8 @@ sub process {
>  				while ($fmt =~ /(\%[\*\d\.]*p(\w))/g) {
>  					$specifier = $1;
>  					$extension = $2;
> -					if ($extension !~ /[SsBKRraEhMmIiUDdgVCbGNOxt]/) {
> +					if ($extension !~ /[SsBKRraEhMmIiUDdgVCbGNOxtf]/ ||
> +					    $extension =~ /^f[^w]/) {

This does not work. $extension seems to have only one character.

Best Regards,
Petr