Re: [PATCH] ramfs: pretend dirent sizes

[Jörn Engel <joern@wohnheim.fh-wedel.de>]

On Wed, 20 July 2005 20:48:17 +0200, Jan Blunck wrote:
> 
> I don't want to tell where these are in general, I need an easy way to 
> seek to the m'th directory + offset position without reading every 
> single dirent. With i_sizes != 0 it is straight forward to use "the sum 
> of the m directory's i_sizes + offset" as the f_pos to seek to. For this 
> purpose it is not necessary to have a "honest" i_size as long as the 
> i_size is bigger than the offset of the last dirent in the directory.

So you use file->offset of the pseudo-directory representing the whole
union stack for two values:
1. level within the union stack we're currently at and
2. offset within the real directory at said level.

And you need a sane value for i_size at every level (but perhaps the
last) to break the converged file->offset apart into (level, offset)
again.  Right?

> >>Reopening the same directory may result in a formerly proper offset
> >>isn't anymore.
> 
> Which is a user problem again. Might be that you are opening a different 
> directory with the same name ... or even a regular file!

Yep.  Two consecutive open() on the "same file" are racy, so anything
could have happened in between.  That's a well-known proplem in
userspace.

Jörn

-- 
Linux is more the core point of a concept that surrounds "open source"
which, in turn, is based on a false concept. This concept is that
people actually want to look at source code.
-- Rob Enderle
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