Getting a block from a block device?

[Stephen Gream]

http://web.archive.org/web/20100711055535/http://cs.anu.edu.au/students/comp3300/ass2.php
That's an old assignment from my uni. It should get you across the
basics of filesystem implementation if you work through it ;)

On Tue, Nov 8, 2011 at 11:12 PM, Alexandru Juncu <alex.juncu at rosedu.org> wrote:
> On Tue, Nov 8, 2011 at 1:56 PM, Dan Luedtke <maildanrl at googlemail.com> wrote:
>> Hallo,
>>
>> On Tue, Nov 8, 2011 at 12:27 PM, Stephen Gream <poisonthemon at gmail.com> wrote:
>>> Once you have the device registered (on /sys or /dev), register a read
>>> callback on the file and use copy_to_user to output the data
>>
>> I read that article you referred to, but I don't think it addresses my
>> problem, as I may have been more clear on what I want to achieve
>> before. Sorry for that!
>> I want to eventually implement a file system, and therefore I am
>> studying the kernel sources to get an idea about all that.
>>
>> Here is my general understanding on how thinks may work :)
>>
>> virtual file system (VFS) <-[1]-> my file system implementation
>> <-[2]-> a block device
>>
>> As I understood, all these subsystems are running in kernel mode.
>>
>> For [1] I read vfs.txt and learned about the VFS-API
>> For [2] I have no idea where I can find the API documentation, however
>> there were some hints on the book "Linux Driver Development" from
>> O'Reilly in chapter "block devices". Nothing really helpful, as they
>> were talking about registering new block devices. I want to use
>> already present devices where I expect my filesystem to be present on.
>> To check that, I have to read the first 512 bytes.
>>
>> The userspace implementation I was talking about previously is
>> something like a mkfs.myfilesystem, that's why i referred to fopen()
>> there.
>>
>> Thank you!
>>
>> Greetings,
>
>
> While in the kernel you would be able to read the blocks from a device
> without using a file path (you don't need to open a file and read from
> it). You will need to interact with the IO System.
>
> I would redirect you to learn about struct gendisk and struct bio.
>