imitation block device in linux

butchie3980 has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: imitation block device in linux by zentara (Cardinal) on Mar 18, 2011 at 14:44 UTC
I may be a bit rusty on my kernel design, but I believe kernel code becomes involved when you use block devices. You may need to write a device driver for the kernel and learn about major and minor devices. Read "man makedev". IIRC there is a mini-tutorial somewhere out there in the cyber fields, for writing your own linux kernel driver. I'm not really a human, but I play one on earth. Old Perl Programmer Haiku ................... flash japh	[reply]
Re^2: imitation block device in linux by chrestomanci (Priest) on Mar 18, 2011 at 15:37 UTC
If the OP wants to take that road then the O'Reilly book Linux Device Drivers is available. The text is under a liberal open source licence, so you can read it online for free. Another approach would be to create a FUSE filing system, and create an artificial block device or mountable file-system image inside. Having said that, I doubt that the OP really needs to write a block device.	[reply]
Re^3: imitation block device in linux by butchie3980 (Acolyte) on Mar 19, 2011 at 08:32 UTC
Yeah, I'm trying to imitate a block device, one that can be accessed by programs like dd, or even mounted with the mount command. My intention is to intercept read/write/seek operations and manage the data as it goes back and forth (logging, encryption, etc). I was hoping to stay with perl, but it looks like I might have to spend some learning curve on C?	[reply]
Re^4: imitation block device in linux by zentara (Cardinal) on Mar 21, 2011 at 14:51 UTC
Re: imitation block device in linux by chrestomanci (Priest) on Mar 18, 2011 at 12:56 UTC
Are you sure you want a block device? (Like a hard disc), Perhaps you actually need a fifo or a character device. (Like a serial port or a unix named pipe.) I think you need to tell us a bit more about what you are attempting to do. Named pipes are easy to create, just call mkfifo <filename> in your unix shell, or call mkfifo() from the POSIX module. With a named pipe you can setup your script to write into the pipe while other processes read, or vice versa. Pipe are uni-directional, but you can easily create a pair. FUSE is for setting up filing systems. (With files, directories, access controls etc). There are perl modules that will help you setup a FUSE filesystem, and let you create virtual files that give access to information when they are read.	[reply]
Re: imitation block device in linux by salva (Canon) on Mar 18, 2011 at 21:27 UTC
NBD	[reply]
Re^2: imitation block device in linux by butchie3980 (Acolyte) on Mar 19, 2011 at 08:34 UTC
NBD looks very interesting. How would I use perl to make an NBD server that clients can mount?	[reply]
Re^3: imitation block device in linux by salva (Canon) on Mar 19, 2011 at 09:04 UTC
Basically, you write a network server implementing the NBD protocol and then use `nbd-client` to connect and link it to some nbd device. There is little documentation about the NBD protocol, you will have to read the C source code for the nbd-server program. It is a very simple protocol. After some simple handshaking, there are only two kind of messages you have to support: `read` and `write`. Another option would be to write a custom `nbd-client` able to fork and run the server through an anonymous socket (think `socketpair`).	[reply] [d/l] [select]