linux-kernel - Re: [PATCH 001/001] CHAR DRIVERS: a simple device to give daemons a /sys-like interface

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Date:	Sat, 03 Aug 2013 11:12:02 -0700
From:	Bob Smith <bsmith@...uxtoys.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 001/001] CHAR DRIVERS: a simple device to give daemons
 a /sys-like interface

Greg
    Thanks for your reply.  I'll reply to your comments in reverse order.


Greg Kroah-Hartman wrote:
> And how does this have anything to do with /sys?  I can't see any sysfs
> interaction in the code, or am I missing it?

Yes, you are right.  I'll change the subject and brief descriptions to
something like:
"Proxy, a simple bidirectional character device that almost transparently
proxies opens, reads, writes, and closes from one side of the device to
the other side."

I'll take "/sys" from all descriptions of the device, but I might leave it
in the Documentation/proxy.txt file since a major use case of proxy is to
give user space drivers and daemons the same kind of interface the kernel
enjoys with /sys and /proc.  The similarity is very deliberate on my part
for commands like
	echo 1 > /proc/sys/net/ipv4/ip_forward		# procfs
	echo 75 > /dev/motors/left/speed		# proxy dev




Greg Kroah-Hartman wrote:
 > Why not just use the cuse interface instead?  How does this differ from
 > that /dev node interaction?

I am a big fan of FUSE and CUSE but they do not support what I need.  CUSE
is OK if _ALL_ interaction is through its interface.  What is lacking is
an ability to open, say, a USB serial port and add its file descriptor to
CUSE's FD_SET.  This is a pretty deep problem since a CUSE takes away main()
from the application developer.  A CUSE application looks kind of like this:
	main(argc, argv)
	{
		(check and process command line)
		cuse_lowlevel_main(argc, argv, ...)
	}

Another difference is that no language bindings are needed.  There is no
equivalent of libfuse.so.  Since proxy is just a character device and there
are no language bindings, someone could, in the unlikely case it ever made
sense, write a user space device driver in node.js.


thanks
Bob Smith





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