Re: purpose of "." entry in a diretory

[Greg Freemyer <greg.freemyer@xxxxxxxxx>]

On Apr 8, 2005 4:43 PM, Jason Zheng <xin.zheng@xxxxxxxxxxxx> wrote:
> Manu Jose wrote:
> 
> >Hi Jason,
> >               "." represents the current working directory and ".."
> >represents the parent directory of the current working directory . It
> >is useful in various contexts. For example if u r currently in the
> >directory /mnt/foo and want to copy the content of /mnt/foo1 to
> >/mnt/foo just isuue the command " cp -R /mnt/foo1/* . "  .So it is
> >always good to represent the working directory with a short symbol and
> >it is not at all a waste....
> >
> >Manu
> >
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> >
> >
> >
> Let me rephrase my question a little bit: BESIDES the obvious usage of
> "." entry, in terms of the filesystem, what is the purpose of "." entry?
> 
> The obvious answer is that you can refer to the current directory using
> "./", however, in order to look up the "." entry, the kernel must have a
> knowledge of the current directory in the first place, doesn't it? The
> kernel needs the directory table for the current directory to look up
> which inode the "." entry refers to. Doesn't that seem a little
> redundant, since the kernel already knows what the current directory is?
> If the kernel is already caching the current directory table, it might
> as well just cache the current directory's inode.
> 
> Coming back to my original question, does the kernel really need that
> "." entry? or is it purely for the user convenience?
> 
> cheers,
> 
> jz
> 
Jason,

I thought about your question when you first asked it, and again now. 
In a generic sense I can't think of a reason that the '.' entry is
mandatory.  As you say there seem to be ways to track the same info
without have that specific directory entry.

OTOH, I would assume the VFS (virtual file system) component of the
Linux Kernel assumes that it is there.

Greg
--
Greg Freemyer

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