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 <[email protected]>
CC: Nicolas Palix <[email protected]>
CC: [email protected]
Signed-off-by: Li Zhijian <[email protected]>

Author: zhijianli88

scripts/coccinelle/api/device_attr_show.cocci

@@ -1,10 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0-only
 ///
 /// From Documentation/filesystems/sysfs.rst:
-///  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().
+///  show() should only use sysfs_emit() or sysfs_emit_at() when formatting
+///  the value to be returned to user space.
 ///
 // Confidence: High
 // Copyright: (C) 2020 Denis Efremov ISPRAS
@@ -30,26 +28,32 @@ ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
 
 @rp depends on patch@
 identifier show, dev, attr, buf;
+expression BUF, SZ, FORMAT, STR;
 @@
 
 ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	<...
+(
 	return
--		snprintf
-+		scnprintf
-			(...);
+-		snprintf(BUF, SZ, FORMAT, STR);
++		sysfs_emit(BUF, FORMAT, STR);
+|
+	return
+-		snprintf(BUF, SZ, STR);
++		sysfs_emit(BUF, STR);
+)
 	...>
 }
 
 @script: python depends on report@
 p << r.p;
 @@
 
-coccilib.report.print_report(p[0], "WARNING: use scnprintf or sprintf")
+coccilib.report.print_report(p[0], "WARNING: please use sysfs_emit or sysfs_emit_at")
 
 @script: python depends on org@
 p << r.p;
 @@
 
-coccilib.org.print_todo(p[0], "WARNING: use scnprintf or sprintf")
+coccilib.org.print_todo(p[0], "WARNING: please use sysfs_emit or sysfs_emit_at")