[PATCH] sysfs: Add stub sysfs_bin_attr_simple_read() for !CONFIG_SYSFS

[Jason Gunthorpe]

At least dmi_scan.c fails to compile:

../drivers/firmware/dmi_scan.c:764:8: error: use of undeclared identifier 'sysfs_bin_attr_simple_read'
  764 | static BIN_ATTR_SIMPLE_ADMIN_RO(smbios_entry_point);
      |        ^
../include/linux/sysfs.h:383:41: note: expanded from macro 'BIN_ATTR_SIMPLE_ADMIN_RO'
  383 | struct bin_attribute bin_attr_##_name = __BIN_ATTR_SIMPLE_RO(_name, 0400)
      |                                         ^
../include/linux/sysfs.h:376:10: note: expanded from macro '__BIN_ATTR_SIMPLE_RO'
  376 |         .read   = sysfs_bin_attr_simple_read,                           \
      |                   ^
../drivers/firmware/dmi_scan.c:765:8: error: use of undeclared identifier 'sysfs_bin_attr_simple_read'
  765 | static BIN_ATTR_SIMPLE_ADMIN_RO(DMI);
      |        ^
../include/linux/sysfs.h:383:41: note: expanded from macro 'BIN_ATTR_SIMPLE_ADMIN_RO'
  383 | struct bin_attribute bin_attr_##_name = __BIN_ATTR_SIMPLE_RO(_name, 0400)
      |                                         ^
../include/linux/sysfs.h:376:10: note: expanded from macro '__BIN_ATTR_SIMPLE_RO'
  376 |         .read   = sysfs_bin_attr_simple_read,                           \
      |                   ^

Since the only declaration for sysfs_bin_attr_simple_read() is inside the
"#ifdef CONFIG_SYSFS". Add a stub to the #else section too.

Fixes: d48c03198a92 ("sysfs: Add sysfs_bin_attr_simple_read() helper")
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
 include/linux/sysfs.h | 9 +++++++++
 1 file changed, 9 insertions(+)

I don't see a patch for this yet, but I did find a 0-day robot complaint:

https://lore.kernel.org/all/202404200345.eGdn5uxW-lkp@xxxxxxxxx/

diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index a7d725fbf73937..e672a927d650a3 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -750,6 +750,15 @@ static inline int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
 {
 	return 0;
 }
+
+static inline ssize_t sysfs_bin_attr_simple_read(struct file *file,
+						 struct kobject *kobj,
+						 struct bin_attribute *attr,
+						 char *buf, loff_t off,
+						 size_t count)
+{
+	return -EINVAL;
+}
 #endif /* CONFIG_SYSFS */
 
 static inline int __must_check sysfs_create_file(struct kobject *kobj,

base-commit: c58a77fe0ba1b708759338ad8bd3828b75a26035
-- 
2.45.2