Re: [PATCH] coccinelle: api: add device_attr_show script

Re: [PATCH] coccinelle: api: add device_attr_show script

[Markus Elfring]

> +// Confidence: High

Would you like to add any suggestion for a possible patch message?


…
> +virtual report
> +virtual org
> +virtual context
> +virtual patch

+virtual report, org, context, patch

Is such a SmPL code variant more succinct?


…
> +ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	<...
> +*	return snprintf@p(...);
> +	...>
> +}

I suggest to reconsider the selection of the SmPL nest construct.
https://github.com/coccinelle/coccinelle/blob/e06b9156dfa02a28cf3cbf0913a10513f3d163ab/docs/manual/cocci_syntax.tex#L783

Can the construct “<+... … ...+>” become relevant here?


Would you like to consider any further software design consequences
around the safe application of the asterisk functionality in rules
for the semantic patch language?

Regards,
Markus

Re: [PATCH] coccinelle: api: add device_attr_show script

[Julia Lawall]

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On Mon, 15 Jun 2020, Markus Elfring wrote:

> > +// Confidence: High
>
> Would you like to add any suggestion for a possible patch message?
>
>
> …
> > +virtual report
> > +virtual org
> > +virtual context
> > +virtual patch
>
> +virtual report, org, context, patch
>
> Is such a SmPL code variant more succinct?

This doens't matter.

>
>
> …
> > +ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
> > +{
> > +	<...
> > +*	return snprintf@p(...);
> > +	...>
> > +}
>
> I suggest to reconsider the selection of the SmPL nest construct.
> https://github.com/coccinelle/coccinelle/blob/e06b9156dfa02a28cf3cbf0913a10513f3d163ab/docs/manual/cocci_syntax.tex#L783
>
> Can the construct “<+... … ...+>” become relevant here?

<... ...> is fine if the only thing that will be used afterwards is what
is inside the <... ...>

julia

>
>
> Would you like to consider any further software design consequences
> around the safe application of the asterisk functionality in rules
> for the semantic patch language?
>
> Regards,
> Markus
>

Re: coccinelle: api: add device_attr_show script

[Markus Elfring]

>> +virtual report, org, context, patch
>>
>> Is such a SmPL code variant more succinct?
>
> This doens't matter.

Can less duplicate code be a bit nicer?


>>> +ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
>>> +{
>>> +	<...
>>> +*	return snprintf@p(...);
>>> +	...>
>>> +}
>>
>> I suggest to reconsider the selection of the SmPL nest construct.
>> https://github.com/coccinelle/coccinelle/blob/e06b9156dfa02a28cf3cbf0913a10513f3d163ab/docs/manual/cocci_syntax.tex#L783
>>
>> Can the construct “<+... … ...+>” become relevant here?
>
> <... ...> is fine if the only thing that will be used afterwards is what
> is inside the <... ...>

I propose once more to distinguish better if the shown return statement
may be really treated as optional for such a source code search approach
(or not).

Regards,
Markus

Re: [PATCH] coccinelle: api: add device_attr_show script

[Markus Elfring]

> The semantic patch looks fine.

Are there any implementation details waiting on a final clarification
also for this code review?

Regards,
Markus

[PATCH] coccinelle: api: add device_attr_show script

[Denis Efremov]

According to the documentation[1] show() methods of device attributes
should return the number of bytes printed into the buffer. This is
the return value of scnprintf(). show() must not use snprintf()
when formatting the value to be returned to user space. snprintf()
returns the length the resulting string would be, assuming it all
fit into the destination array[2]. scnprintf() return the length of
the string actually created in buf. If one can guarantee that an
overflow will never happen sprintf() can be used otherwise scnprintf().

[1] Documentation/filesystems/sysfs.txt
[2] "snprintf() confusion" https://lwn.net/Articles/69419/

Signed-off-by: Denis Efremov <efremov@linux.com>
---
 scripts/coccinelle/api/device_attr_show.cocci | 55 +++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 scripts/coccinelle/api/device_attr_show.cocci

diff --git a/scripts/coccinelle/api/device_attr_show.cocci b/scripts/coccinelle/api/device_attr_show.cocci
new file mode 100644
index 000000000000..d8ec4bb8ac41
--- /dev/null
+++ b/scripts/coccinelle/api/device_attr_show.cocci
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0-only
+///
+/// From Documentation/filesystems/sysfs.txt:
+///  show() must not use snprintf() when formatting the value to be
+///  returned to user space. If you can guarantee that an overflow
+///  will never happen you can use sprintf() otherwise you must use
+///  scnprintf().
+///
+// Confidence: High
+// Copyright: (C) 2020 Denis Efremov ISPRAS
+// Options: --no-includes --include-headers
+//
+
+virtual report
+virtual org
+virtual context
+virtual patch
+
+@r depends on !patch@
+identifier show, dev, attr, buf;
+position p;
+@@
+
+ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	<...
+*	return snprintf@p(...);
+	...>
+}
+
+@rp depends on patch@
+identifier show, dev, attr, buf;
+@@
+
+ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	<...
+	return
+-		snprintf
++		scnprintf
+			(...);
+	...>
+}
+
+@script: python depends on report@
+p << r.p;
+@@
+
+coccilib.report.print_report(p[0], "WARNING: use scnprintf or sprintf")
+
+@script: python depends on org@
+p << r.p;
+@@
+
+coccilib.org.print_todo(p[0], "WARNING: use scnprintf or sprintf")
-- 
2.26.2