Mapping of Filename to allocated blocks

[Luis de Bethencourt]

On 28/04/16 04:32, arshad hussain wrote:
> On Thu, Apr 28, 2016 at 7:28 AM, Manoj Rao <linux at manojrajarao.com> wrote:
>> Hi All,
>>
>> I'm looking for a way to get a filename associated with a given physical
>> block (ideally what I'd like is a mapping of filename <=> all the allocated
>> blocks for this file).
> 
> If you have not done already, this could be a good starting point.
> Look at FIBMAP IOCTL.
> 
> Here is one usage of FIEMAP, demonstrated via hdparam.
> # hdparm --fibmap <your file name>
> 
>>
>> Is there a recommended way to do this already in kernel? if not, then where
>> should I start looking to add changes?
> 
> Not sure about what would be the Recommended method. But this could be done
> in user-space vs doing it in kernel space. For example, consider cases like
> single file restore - there will be a requirement to figure out the
> logical - physical block allocation for a file which could be achieved
> through...
> Read superblock
> Read dentry - Home into the required inode (file)
> Read inode - to figure out the location of block.
> 
> Note: This is not generic - and would require changes as layout is different
> for filesystems.
> 
> Thanks
> Arshad
> 

If you are going to create anything based on VFS (Virtual File Switch), I
recommend reading this article from LWN.

https://lwn.net/Articles/57369/

Even create a small memory-bound file system to get comfortable with the API.

If you want a version that works with current mainline, check out:
https://github.com/luisbg/toy_kernel_modules/blob/master/toyfs/toyfs.c

Sorry it doesn't have comments yet, I will be adding those very soon.

Happy hacking,
Luis