Re: [PATCH 06/26] elevate write count open()'d files

[Christoph Hellwig <hch@infradead.org>]

On Fri, Jun 22, 2007 at 01:03:10PM -0700, Dave Hansen wrote:
> 
> This is the first really tricky patch in the series.  It
> elevates the writer count on a mount each time a
> non-special file is opened for write.
> 
> This is not completely apparent in the patch because the
> two if() conditions in may_open() above the
> mnt_want_write() call are, combined, equivalent to
> special_file().
> 
> There is also an elevated count around the vfs_create()
> call in open_namei().  The count needs to be kept elevated
> all the way into the may_open() call.  Otherwise, when the
> write is dropped, a ro->rw transisition could occur.  This
> would lead to having rw access on the newly created file,
> while the vfsmount is ro.  That is bad.

Looks good.

> 
> Some filesystems forego the use of normal vfs calls to create
> struct files.  Make sure that these users elevate the mnt writer
> count because they will get __fput(), and we need to make
> sure they're balanced.

With this you mean ipc/mqueue.c?  You should probably mention
that single bastard child of a wannabe-filesystem explicitly :)