Re: + switch-ntfs-to-touch_atime.patch added to -mm tree

[Christoph Hellwig <hch@lst.de>]

[ccing -fsdevel now because this is something of interest to the public]

On Mon, Nov 07, 2005 at 09:51:08PM +0000, Anton Altaparmakov wrote:
> What callers are those?  I am curious...  The SUS/Posix standard requires 
> it as I said in previous post (except for the no size change case but 
> as I also said in previous post the VFS does that wrong in same way as 
> ntfs and I just copied vfs)...

Besides the various ->setattr instaces which are supposed to set ctime if
ATTR_SIZE|ATTR_CTIME are set (which it is for sys_truncate or
sys_ftruncate but possibly not nfsd requests) generic_file_buffered_write()
calls vmtruncate and thus ->truncate without asking for ctime updates.

The point here is to repeat that the nth time is that you are doing
things in ->truncate that you shouldn't do there.  Just move your
updates of the base inode to ->setattr, and update ->i_ctime directly
like all the other filesystems do instead of using inode_update_time
which contains an optimization that's only usefull for a codepath like
write where the ctime/mtime update happens very frequently.

Your use of the function is wrong no matter whether it takes a struct
file or struct inode.

> > so just update them directly for those callers.
> 
> That is difficult to do as VFS ->truncate() does not allow an error to be 
> returned.  And the setting must only happen on success for {f,}truncate().
> 
> Thus vmtruncate() always returns success even when ->truncate() failed, so 
> VFS _cannot_ be compliant with standard unless it is changed so that 
> ->truncate() can return error and vmtruncate() passes that upward to 
> ->setattr().  Otherwise you have to do the cmtime updates from 
> ->truncate() on success and not do them on failure.

so please submit a patch to allow an error return from ->truncate.