Thread: Block device I/O under linux, can someone point me in the right direction?

Hello everybody!

Well, I have been doing a lot of reading about the Linux kernel and am currently interested in writing some programs that perform low level block device IO. Specifically, I want to write a simple ISO burning program to burn an image made from mkisofs. The problem I am having is that I don't know where to turn next for reference material, mostly concerning actual implementation of device I/O with non character devices. For instance, where can I find good reference material for devices I am trying to program for? Do companies like Memorex have documentation available for their drives? I have read books that touch on block device I/O and most of them are far too vague to tell me what I want.

Basically what I am asking is for someone to possibly save me some time researching everything. For now I am reading through the source code to wodim (a cdrecord like program) but this is obviously not the ideal way to learn how block device IO is actually implemented. I have started reading some books, one of which is Linux Device Drivers, and this is a very good book but at the moment I am concentrating on a higher level. I want to use linux/cdrom.h to do this and I feel that I am just missing some reading that could really help me get going.

Thanks for reading this spur of the moment post, and I hope everyone understands what I mean when I say I am lacking reference material.

I think I may have skipped over that one since it is so commonly title. Anyway, I looks like a good resource, plus its a free online book!

Well, I think that book as well doesn't go where I want.

It briefly mentions open(),read(),write() and related calls and their uses. I need to know how to use those same functions, but to properly initialize a cd drive first and then write data to that drive. A lot of resources I find aren't helping me much. Reading through the wodim source code is telling me a lot, but there is also way more information their than I am actually after. So I am sifting through lots of un-wanted code.

Originally Posted by matsp

I had a quick look at http://lxr.linux.no/source/drivers/cdrom/cdrom.c

But it looks like writes are actually performed through the regular IDE/SCSI interface.

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Mats

Thats the information I am after. A good reference for reading/writing to devices under the IDE/SCSI interface. Like I said, I am learning everything here quite slow since I am doing so much looking in other code.

Yes. I see that. The problem I am having is this.

I know I need to open() the device, and then write my data, but doing this as if it were another normal file does not work. I need to use a combination of ioctl() calls as preparation and then write() my data. What I need to research is how to know that actual procedure for doing so with a given device?

For instance: With X brand CDRW drive you need to call A,B, and C iotctl() calls before a write.

Now I know how I will need to deal with sectors of bytes, however, my confusion lies in the specific interaction with the hardware.

UPDATE:

Well, I finally found what I was looking for. I wanted to write a program that burns a compact disc. I just got quite confused because I jumped head first into digging through source code and sort of got lost.

Anyway, I found the Linux SCSI driver, sg:

Linux SCSI Driver HOWTO

Hopefully this post helps someone else in the future.