sysfs vs configfs



\kernel\Documentation\filesystems\configfs\configfs.txt

[What is configfs?]

configfs is a ram-based filesystem that provides the converse of
sysfs's functionality.  Where sysfs is a filesystem-based view of
kernel objects, configfs is a filesystem-based manager of kernel
objects, or config_items.

With sysfs, an object is created in kernel (for example, when a device
is discovered) and it is registered with sysfs.  Its attributes then
appear in sysfs, allowing userspace to read the attributes via
readdir(3)/read(2).  It may allow some attributes to be modified via
write(2).  The important point is that the object is created and
destroyed in kernel, the kernel controls the lifecycle of the sysfs
representation, and sysfs is merely a window on all this.

A configfs config_item is created via an explicit userspace operation:
mkdir(2).  It is destroyed via rmdir(2).  The attributes appear at
mkdir(2) time, and can be read or modified via read(2) and write(2).
As with sysfs, readdir(3) queries the list of items and/or attributes.
symlink(2) can be used to group items together.  Unlike sysfs, the
lifetime of the representation is completely driven by userspace.  The
kernel modules backing the items must respond to this.

Both sysfs and configfs can and should exist together on the same
system.  One is not a replacement for the other.