Actual usage of files in ubifs

[Richard Weinberger]

Ricard,

Am Dienstag, 12. September 2017, 11:15:25 CEST schrieb Ricard Wanderlof:
> On Mon, 11 Sep 2017, Richard Weinberger wrote:
> > Am Montag, 11. September 2017, 17:44:09 CEST schrieb Artem Bityutskiy:
> > > > Good point. I was solely thinking along the lines of how much space
> > > > the
> > > > actual file occupied, not considering metadata. That would be a good
> > > > starting point. I'm guessing that for moderate file sizes the
> > > > metadata
> > > > would be relatively small compared to the file itself?
> > > 
> > > I would think a "slow" version of this would not be that hard to
> > > implement - walk the index and sum up node sizes. Subtract header sizes
> > > if you do not want metadata.
> > > 
> > > I am not sure what would be the API? Do other FSes implement something
> > > like this?
> > 
> > I think a "show MTD usage by inode" should be implementable via debugfs.
> > Maybe, after a discussion on linux-fsdevel a per-file ioctl().
> > 
> > But first I'd like to know more about the use-case and where to draw the
> > border. e.g. If a file as xattrs, do you also account them? UBIFS
> > modules xattrs via inodes. So, they have a rather huge space overhead.
> 
> In our specific situation the use case is basically that given a specific
> set files (in the root file system), how much flash is actually needed,
> also considering that different types of files have different compression
> ratios depending on the content. I.e. a large text file might not hurt as
> much as a large binary since the former compresses better.
> 
> So primarily it is the total amount needed for the whole file system, but
> it quickly comes down how much individual files consume. In our case it's
> not necessary to do the operation on a running file system, but in the
> more general case that might be more useful.
> 
> I would think that this is something that is known somewhere inside
> mkfs.ubifs, or is the information too convoluted to be easily extractable?

Adding this to mkfs.ubifs shouldn't be a big deal.
And I agree your use case makes sense.

Do you want to send me a patch? :)

Thanks,
//richard

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