Clarification regarding design of a device.

Hi,

I have say a crypto device and if I pass a data stream assuming echo "test"

opens the same device twice should and pass different streams should I differentiate those 2 streams and have encrypted buffers of these 2 streams as output? If yes how should I differentiate it? Or should I not differentiate and provide different devices say aes0,aes1 or should the userspace program worry about locking and sharing of resource?

Thanks.

Hi...

I am not keen regarding char/block device management, but I think you should separate those streams.

How? Well, same thing like you open a same file twice, right? You're given two different file descriptor. After all, the "open", "read" and "write" handler of device IMHO always assume that we wanna achieve such different stream, right?

regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

Although given two file descriptors when I write some content it will be on the same file right? Shouldn't the same file analogy apply?

I thought about using file descriptors to separate streams, but have to take care of ensuring completion of processing the buffer when closed. This I feel should be done if the descriptor gets reused.

Sounds silly but how do I get access to the file descriptor?

Also If I make the user create a session for an operation similar to this paper
http://www.usenix.org/event/usenix03/tech/full_papers/keromytis/keromytis_html/node8.html#SECTION00042000000000000000,
should I remove the read, write operations and do all operations using ioctl commands i.e. reading the user buffer etc?

Hi :)

to the best I know, kernel assign it for you and you access it from the give file structure. For example, look at open handler fs/proc/cpuinfo.c. You will see these:
static int cpuinfo_open(struct inode *inode, struct file *file)

Ok, I revise, perhaps not filedescriptor, but file structure itself.

There's a plus and minus of simply using ioctl for all read and write. IMHO, ioctls are needed if you need various "sub command" toward the device file, i.e if I took KVM for example: to setup new guest structure, to ask for memory and so on. So, if you don't really need to do such "extra" things, I believe it's better to still use read/write handler for read/write operation.

regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com