[PATCH v2 1/3] sysfs: Invoke iomem_get_mapping() from the sysfs open callback

["Krzysztof Wilczyński" <kw@linux.com>]

Defer invocation of the iomem_get_mapping() to the sysfs open callback
so that it can be executed as needed when the binary sysfs object has
been accessed.

To do that, convert the "mapping" member of the struct bin_attribute
from a pointer to the struct address_space into a function pointer with
a signature that requires the same return type, and then updates the
sysfs_kf_bin_open() to invoke provided function should the function
pointer be valid.

Thus, this change removes the need for the fs_initcalls to complete
before any other sub-system that uses the iomem_get_mapping() would be
able to invoke it safely without leading to a failure and an Oops
related to an invalid iomem_get_mapping() access.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
---
 fs/sysfs/file.c       | 2 +-
 include/linux/sysfs.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 9aefa7779b29..a3ee4c32a264 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -175,7 +175,7 @@ static int sysfs_kf_bin_open(struct kernfs_open_file *of)
 	struct bin_attribute *battr = of->kn->priv;
 
 	if (battr->mapping)
-		of->file->f_mapping = battr->mapping;
+		of->file->f_mapping = battr->mapping();
 
 	return 0;
 }
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index d76a1ddf83a3..fbb7c7df545c 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -170,7 +170,7 @@ struct bin_attribute {
 	struct attribute	attr;
 	size_t			size;
 	void			*private;
-	struct address_space	*mapping;
+	struct address_space *(*mapping)(void);
 	ssize_t (*read)(struct file *, struct kobject *, struct bin_attribute *,
 			char *, loff_t, size_t);
 	ssize_t (*write)(struct file *, struct kobject *, struct bin_attribute *,
-- 
2.32.0