[Gnu-arch-users] Re: extended attributes

[Aaron Bentley]

Tom Lord wrote:

>    > From: Aaron Bentley <address@hidden>
>
>    > Perhaps a fully transactional filesystem was never what was needed. 
>    > Maybe all that's needed is a variant of rename(2) that only changes the
>    > number of links, atime and mtime.
>
> Huh?  Can you explain in more detail what you are thinking of because
> I don't get it from that description.   
>  
For atomic file updates, rename(2) does too much.  It modifies or 
creates a directory entry to have default ownership, permissions and 
time values.

> mtime?   really?  What?!?

I mean "file modification time" from struct stat's st_mtime.

A variant of rename could be called move_contents().  It would simply do 
less.  Not change ownership, permissions or file creation time.  But it 
could change #of links, would change inode, modification time and access 
time.  An update done with open() and write()  would not change inode or 
links, but I think this is as close as you can get to atomic updates 
without adding locks or another layer of indirection.

>    > Well, yes.  But some things that could be quickly implemented were not
>    > because the need wasn't apparent.
>
> Sure.  Informally, it feels like the original idea was "every file is
> a sequence of bytes; directories being files that can only be written
> to via dir-modifying system calls" and then it's all downhill from
> there.  (You know, extended attributes ain't nothing -- you can
> probably still find people with principled objections to symlinks.)
>  
Ah, diversity.  I guess I'm a primitive for using vim.  I've used edlin 
too, but not ed.

Aaron