Re: [9fans] long filenames in cwfs

[Skip Tavakkolian <skip.tavakkolian@gmail.com>]

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with 8K names, using base64, one could encode 6111 bytes of data in the
name. i just did a quick inventory[*] of my $home; 74% of my files have
less than 6112 bytes of data.

[*]
% fn pctfileslessthan6k () {
x=`{du -na $home|wc -l}
y=`{du -na $home|awk '$1 < 6112 {print $0}'|wc -l}
pct=`{echo '2k ' $y $x ' / 100 * p' | dc}
echo $pct
}
% pctfileslessthan6k
74.00
%


On Sun, Jun 23, 2013 at 7:08 AM, erik quanstrom <quanstro@quanstro.net>wrote:

> On Sun Jun 23 09:38:01 EDT 2013, arisawa@ar.aichi-u.ac.jp wrote:
> > Thank you cinap,
> >
> > I tried to copy all my  Dropbox data to cwfs.
> > the number of files that exceeded 144B name limit was only 3 in 40000
> files.
> > I will be happy if cwfs64x natively accepts longer name, but the
> requirement
> > is almost endless. for example, OSX support 1024B names.
> > I wonder if making NAMELEN larger is the only way  to handle the problem.
>
> without a different structure, it is the only way to handle the problem.
>
> a few things to keep in mind about file names.  file names when they
> appear in 9p messages can't be split between messages.  this applies
> to walk, create, stat or read (of parent directory).  i think this places
> the restriction that maxnamelen <= IOUNIT - 43 bytes.  the distribution
> limits IOUNIT through the mnt driver to 8192+24.  (9atom uses
> 6*8k+24)
>
> there are two basic ways to change the format to deal with this
> 1.  provide an escape to point to auxillary storage.  this is kind to
> existing storage.
> 2.  make the name (and thus the directory entry) variable length.
>
> on our fs (which has python and some other nasties), the average
> file length is 11.  making the blocks variable length could save 25%
> (62 directory entries per buffer).  but it might be annoying to have
> to migrate the whole fs.
>
> so since there are so few long names, why not waste a whole block
> on them?  if using the "standard" (ish) 8k raw block size (8180 for
> data), the expansion of the header could be nil (through creative
> encoding) and there would be 3 extra blocks taken for indirect names.
> for your case, the cost for 144-byte file names would be that DIRPERBUF
> goes from 47 to 31.  so most directories > 31 entries will take
> 1.5 x (in the big-O sense) their original space even if there are
> no long names.
>
> - erik
>
>

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