Re: [PATCH] prune_icache_sb

[Wendy Cheng]

Russell Cattelan wrote:
> Wendy Cheng wrote:
>
> > Linux kernel, particularly the VFS layer, is starting to show signs 
> > of inadequacy as the software components built upon it keep growing. 
> > I have doubts that it can keep up and handle this complexity with a 
> > development policy like you just described (filesystem is a dumb 
> > layer ?). Aren't these DIO_xxx_LOCKING flags inside 
> > __blockdev_direct_IO() a perfect example why trying to do too many 
> > things inside vfs layer for so many filesystems is a bad idea ? By 
> > the way, since we're on this subject, could we discuss a little bit 
> > about vfs rename call (or I can start another new discussion thread) ?
> >
> > Note that linux do_rename() starts with the usual lookup logic, 
> > followed by "lock_rename", then a final round of dentry lookup, and 
> > finally comes to filesystem's i_op->rename call. Since lock_rename() 
> > only calls for vfs layer locks that are local to this particular 
> > machine, for a cluster filesystem, there exists a huge window between 
> > the final lookup and filesystem's i_op->rename calls such that the 
> > file could get deleted from another node before fs can do anything 
> > about it. Is it possible that we could get a new function pointer 
> > (lock_rename) in inode_operations structure so a cluster filesystem 
> > can do proper locking ?
>
> It looks like the ocfs2 guys have the similar problem?
>
> http://ftp.kernel.org/pub/linux/kernel/people/mfasheh/ocfs2/ocfs2_git_patches/ocfs2-upstream-linus-20060924/0009-PATCH-Allow-file-systems-to-manually-d_move-inside-of-rename.txt 

Thanks for the pointer. Same as ocfs2, under current VFS code, both 
GFS1/2 also need FS_ODD_RENAME flag for the rename problem - got an ugly 
~200 line draft patch ready for GFS1 (and am looking into GFS2 at this 
moment). The issue here is, for GFS, if vfs lock_rename() can call us, 
this complication can be greatly reduced. Will start another thread to 
see whether the wish can be granted.

-- Wendy

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