Hi Christoph.
On Mon, Sep 10, 2018 at 09:50:39AM +0200, Christoph Hellwig wrote:
> On Thu, Sep 06, 2018 at 10:31:05AM +0200, Carlos Maiolino wrote:
> >
> > Sorry, I'm not 100% sure I followed your point here, do you mind to detail it a
> > bit?
> > Passing fiemap_fill_next_extent() as a pointer to what? ->fiemap() interface?
>
> Yes.
>
> > Sounds interesting, but doing this looks like I'll need to do what I was trying
> > to avoid from the beginning, which is the creating of a second struct
> > fiemap_extent_info, to be used in-lernel only, so, the last field doesn't need
> > to be tagged as __user. I'm ok with that though, I was just trying a way to
> > avoid adding unneeded data structures if possible, but looks like it ended up
> > not being a good approach :P
>
> fieinfo is mostly used as an opaqueue cookie, so I think it should
> be possible to just pass a void pointer to fiemap and only let the 'filler'
> callback (that is fiemap_fill_next_extent or whatever a kernel caller
> passed) interpret it.
>
> The only thing breaking this right now seems to be fi_flags, so maybe
> we just need to pass that explicitly as another argument to ->fiemap.
>
> Something like:
>
> typedef int (fiemap_fill_cb)(struct inode *inode, void *data, u64 logical,
> u64 phys, u64 len, u32 flags);
>
> struct file_operations {
> ...
> int (*fiemap)(struct inode *, unsigned int, fiemap_fill_cb,
> void *, u64 start, u64 len);
> ...
> };
I've been playing around with this idea, and one thing that I've been having
problems with (at least that I'm not liking the end result), is the fact some
filesystems keep juggling with the *fiemap_extent_info passed to them. Like
ext4, for example, where it takes the pointer and passes it to its internal
functions or to generic_block_fiemap if that's the case.
I was wondering if, maybe, creating a new structure to embed the cookie, the
flags, and the fill callback wouldn't be better, I've been thinking it might be
easier to refactor the code needed to handle this new structure with all needed
data into it, instead of handling the callback, flags and the cookie by their
own. Maybe even create some helpers to handle the data into it.
What you think?
--
Carlos
