Getting a block from a block device?

[manishrma@gmail.com (mani)]

if you wanna open a block device specificallyy
you can look into fs/block_dev.c

struct block_device *open_bdev_exclusive(const char *path, fmode_t mode,
void *holder)

Also i think if you are interested in reading the first sector
then you can probably check the block/genhd.c file
get the disk (i.e struct genhd) then the partition (struct hdpart)
you will be able to get the first sector.

Thanks

On Tue, Nov 8, 2011 at 5:29 PM, rohan puri <rohan.puri15@gmail.com> wrote:

>
>
> On Tue, Nov 8, 2011 at 5:26 PM, Dan Luedtke <maildanrl@googlemail.com>wrote:
>
>> Hallo,
>>
>> On Tue, Nov 8, 2011 at 12:27 PM, Stephen Gream <poisonthemon@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,
>>
>> Dan
>> --
>> Dan Luedtke
>> http://www.danrl.de
>>
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>>
> Dan,
>
> You need to look at other block-based file systems in the kernel sources
> in fs dir for examples and understand how they do it.
>
> Regards,
> Rohan Puri
>
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