[PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[Joel Becker]

Folks,
	I humbly submit configfs.  With configfs, 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).  readdir(3)
queries the list of items and/or attributes.
	The lifetime of the filesystem representation is completely
driven by userspace.  The lifetime of the objects themselves are managed
by a kref, but at rmdir(2) time they disappear from the filesystem.
	configfs is not intended to replace sysfs or procfs, merely to
coexist with them.
	An interface in /proc where the API is: 

	# echo "create foo 1 3 0x00013" > /proc/mythingy

or an ioctl(2) interface where the API is:

	struct mythingy_create {
		char *name;
		int index;
		int count;
		unsigned long address;
	}

	do_create {
		mythingy_create = {"foo", 1, 3, 0x0013};
		return ioctl(fd, MYTHINGY_CREATE, &mythingy_create);
	}

becomes this in configfs:

	# cd /config/mythingy
	# mkdir foo
	# echo 1 > foo/index
	# echo 3 > foo/count
	# echo 0x00013 > foo/address

	Instead of a binary blob that's passed around or a cryptic
string that has to be formatted just so, configfs provides an interface
that's completely scriptable and navigable.
	Patch is against 2.6.12-rc1-bk3.

http://oss.oracle.com/~jlbec/files/configfs/2.6.12-rc1-bk3/configfs-2.6.12-rc1-bk3-1.patch

Joel

-- 

"Not everything that can be counted counts, and not everything
 that counts can be counted."
        - Albert Einstein 

Joel Becker
Senior Member of Technical Staff
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127

Re: [PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[Joel Becker]

On Sun, Apr 03, 2005 at 12:57:28PM -0700, Joel Becker wrote:
> 	I humbly submit configfs.  With configfs, a configfs
> ...
> 	Patch is against 2.6.12-rc1-bk3.

	Updated for bk5 and the new backing_dev capabilites mask:

http://oss.oracle.com/~jlbec/files/configfs/2.6.12-rc1-bk5/configfs-2.6.12-rc1-bk5-1.patch

Joel

-- 

"Against stupidity the Gods themselves contend in vain."
	- Freidrich von Schiller

Joel Becker
Senior Member of Technical Staff
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127

Re: [PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[Arjan van de Ven]

On Sun, 2005-04-03 at 12:57 -0700, Joel Becker wrote:
> Folks,
> 	I humbly submit configfs.  With configfs, 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).  readdir(3)
> queries the list of items and/or attributes.
> 	The lifetime of the filesystem representation is completely
> driven by userspace.  The lifetime of the objects themselves are managed
> by a kref, but at rmdir(2) time they disappear from the filesystem.

does that mean you rmdir a non-empty directory ??

Re: [PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[Matt Mackall]

On Sun, Apr 03, 2005 at 12:57:28PM -0700, Joel Becker wrote:
> Folks,
> 	I humbly submit configfs.  With configfs, 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).  readdir(3)
> queries the list of items and/or attributes.
> 	The lifetime of the filesystem representation is completely
> driven by userspace.  The lifetime of the objects themselves are managed
> by a kref, but at rmdir(2) time they disappear from the filesystem.
> 	configfs is not intended to replace sysfs or procfs, merely to
> coexist with them.
> 	An interface in /proc where the API is: 
> 
> 	# echo "create foo 1 3 0x00013" > /proc/mythingy
> 
> or an ioctl(2) interface where the API is:
> 
> 	struct mythingy_create {
> 		char *name;
> 		int index;
> 		int count;
> 		unsigned long address;
> 	}
> 
> 	do_create {
> 		mythingy_create = {"foo", 1, 3, 0x0013};
> 		return ioctl(fd, MYTHINGY_CREATE, &mythingy_create);
> 	}
> 
> becomes this in configfs:
> 
> 	# cd /config/mythingy
> 	# mkdir foo
> 	# echo 1 > foo/index
> 	# echo 3 > foo/count
> 	# echo 0x00013 > foo/address
> 
> 	Instead of a binary blob that's passed around or a cryptic
> string that has to be formatted just so, configfs provides an interface
> that's completely scriptable and navigable.

How does the kernel know when to actually create the object?

-- 
Mathematics is the supreme nostalgia of our time.

Re: [PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[Zach Brown]

Arjan van de Ven wrote:
> On Sun, 2005-04-03 at 12:57 -0700, Joel Becker wrote:
> 
>>Folks,
>>	I humbly submit configfs.  With configfs, 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).  readdir(3)
>>queries the list of items and/or attributes.
>>	The lifetime of the filesystem representation is completely
>>driven by userspace.  The lifetime of the objects themselves are managed
>>by a kref, but at rmdir(2) time they disappear from the filesystem.
> 
> 
> does that mean you rmdir a non-empty directory ??

Yeah, but only attributes and default groups are automatically torn
down.  You can't rmdir() an item that is the destination of links and
you can't rmdir() groups that still contain items.

- z

Re: [PATCH] configfs, a filesystem for userspace-driven kernel object configuration

[Zach Brown]

Matt Mackall wrote:
> On Sun, Apr 03, 2005 at 12:57:28PM -0700, Joel Becker wrote:
> 

>>	An interface in /proc where the API is: 

>>or an ioctl(2) interface where the API is:

>>
>>becomes this in configfs:
>>
>>	# cd /config/mythingy
>>	# mkdir foo
>>	# echo 1 > foo/index
>>	# echo 3 > foo/count
>>	# echo 0x00013 > foo/address
>>
>>	Instead of a binary blob that's passed around or a cryptic
>>string that has to be formatted just so, configfs provides an interface
>>that's completely scriptable and navigable.
> 
> How does the kernel know when to actually create the object?

"actually create", huh? :)

In the trivial case Joel describes, the item is almost certainly
allocated during "# mkdir foo" when the subsystem will get a
->make_item() call for the 'mythingy' group it registerd.  The various
attribute writes then find the item by following their
configfs_attribute argument to the item that its embedded in.

But I bet you're not really asking about creation.  I bet you're
wondering how the kernel will know when enough attributes have been
filled and that it's safe to use the object.  Misguided items could
assign magical ordering to the attribute filling such that once a final
attribute is set, and others have been set, the item goes live.  That's
what ocfs2 does now, sadly, but certainly not as a long-term solution.

The missing piece is the 'commit_item' group operation that is yet to be
implemented.  The intent is to have a directory of pending items that
can have their attributes filled before being rename()ed into a
directory of items that are in active use.  The commit_item() call that
hits at rename() would give the kernel the chance to refuse the item
because attributes haven't been filled in or conflict with existing
items, or whatever.

- z