coccinelle: device_attr_show: Remove useless expression STR

Commit ff82e84e80fc ("coccinelle: device_attr_show: simplify patch case")
simplifies the patch case, as a result, STR is no longer needed.

This also helps to fix below coccicheck warning:
> warning: rp: metavariable STR not used in the - or context code

CC: Julia Lawall <Julia.Lawall@inria.fr>
CC: Nicolas Palix <nicolas.palix@imag.fr>
CC: cocci@inria.fr
Fixes: ff82e84e80fc ("coccinelle: device_attr_show: simplify patch case")
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

coccinelle: device_attr_show: simplify patch case

Replacing the final expression argument by ... allows the format
string to have multiple arguments.

It also has the advantage of allowing the change to be recognized as
a change in a single statement, thus avoiding adding unneeded braces.

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

coccinelle: device_attr_show: Adapt to the latest Documentation/filesystems/sysfs.rst

Adapt description, warning message and MODE=patch according to the latest
Documentation/filesystems/sysfs.rst:
> show() should only use sysfs_emit() or sysfs_emit_at() when formatting
> the value to be returned to user space.

After this patch:
When MODE=report,
$ make coccicheck COCCI=scripts/coccinelle/api/device_attr_show.cocci M=drivers/hid/hid-picolcd_core.c MODE=report
<...snip...>
drivers/hid/hid-picolcd_core.c:304:8-16: WARNING: please use sysfs_emit or sysfs_emit_at
drivers/hid/hid-picolcd_core.c:259:9-17: WARNING: please use sysfs_emit or sysfs_emit_at

When MODE=patch,
$ make coccicheck COCCI=scripts/coccinelle/api/device_attr_show.cocci M=drivers/hid/hid-picolcd_core.c MODE=patch
<...snip...>
diff -u -p a/drivers/hid/hid-picolcd_core.c b/drivers/hid/hid-picolcd_core.c
--- a/drivers/hid/hid-picolcd_core.c
+++ b/drivers/hid/hid-picolcd_core.c
@@ -255,10 +255,12 @@ static ssize_t picolcd_operation_mode_sh
{
struct picolcd_data *data = dev_get_drvdata(dev);

- if (data->status & PICOLCD_BOOTLOADER)
- return snprintf(buf, PAGE_SIZE, "[bootloader] lcd\n");
- else
- return snprintf(buf, PAGE_SIZE, "bootloader [lcd]\n");
+ if (data->status & PICOLCD_BOOTLOADER) {
+ return sysfs_emit(buf, "[bootloader] lcd\n");
+ }
+ else {
+ return sysfs_emit(buf, "bootloader [lcd]\n");
+ }
}

static ssize_t picolcd_operation_mode_store(struct device *dev,
@@ -301,7 +303,7 @@ static ssize_t picolcd_operation_mode_de
{
struct picolcd_data *data = dev_get_drvdata(dev);

- return snprintf(buf, PAGE_SIZE, "hello world\n");
+ return sysfs_emit(buf, "hello world\n");
}

static ssize_t picolcd_operation_mode_delay_store(struct device *dev,

CC: Julia Lawall <Julia.Lawall@inria.fr>
CC: Nicolas Palix <nicolas.palix@imag.fr>
CC: cocci@inria.fr
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>

scripts: device_attr_show.cocci: update location of sysfs doc

sysfs.txt was converted and renamed to sysfs.rst.

Update device_attr_show.cocci script accordingly.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/048ed24b09aefa0051d76396d6250e35e6ba035c.1599660067.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

coccinelle: api: add device_attr_show script

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>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>