Re: truncate(2) sometimes updates ctime and sometimes ctime and mtime!

[Linus Torvalds <torvalds@osdl.org>]

On Fri, 30 Sep 2005, Anton Altaparmakov wrote:
> 
> There is an inconsistency in the way truncate works which was introduced
> (relatively) recently.
> 
> fs/open.c::sys_truncate
>   -> do_sys_truncate
>     -> do_truncate does:
> 
>         newattrs.ia_size = length;
>         newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME;
> 
>         down(&dentry->d_inode->i_sem);
>         err = notify_change(dentry, &newattrs);
>         up(&dentry->d_inode->i_sem);
> 
> This changes the ctime only.

Hmm.. That looks wrong, partly because I don't think it should even set 
ATTR_CTIME _either_. However, I don't see any recent changes to that code, 
so it must have been logn for a long time. That line in do_truncate() has 
been like that since at _least_ 2002.

So what changed to make you notice?

The _code_ actually expects the low-level filesystem to just do it when it 
does the actual truncate itself. That's certainly what ext3 does, for 
example.

A comment or two to that effect might be useful, though.

In other words: some attributes are "implicit". For example, mtime is 
supposed to be set automatically by the filesystem whenever it sees a 
write. The VFS layer will _not_ do a "inode state notify" event for that. 

The same is true of truncation.

But I agree that it's inconsistent. Anybody have any deep opinions?

		Linus
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