Re: [PATCH v4 01/22] fs: Add generic_atomic_write_valid_size()

[John Garry]

On 12/06/2024 22:10, Darrick J. Wong wrote:
> On Fri, Jun 07, 2024 at 02:38:58PM +0000, John Garry wrote:
> > Add a generic helper for FSes to validate that an atomic write is
> > appropriately sized (along with the other checks).
> >
> > Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
> > ---
> >   include/linux/fs.h | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 069cbab62700..e13d34f8c24e 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -3645,4 +3645,16 @@ bool generic_atomic_write_valid(loff_t pos, struct iov_iter *iter)
> >   	return true;
> >   }
> >   
> > +static inline
> > +bool generic_atomic_write_valid_size(loff_t pos, struct iov_iter *iter,
> > +				unsigned int unit_min, unsigned int unit_max)
> > +{
> > +	size_t len = iov_iter_count(iter);
> > +
> > +	if (len < unit_min || len > unit_max)
> > +		return false;
> > +
> > +	return generic_atomic_write_valid(pos, iter);
> > +}
>
> Now that I look back at "fs: Initial atomic write support" I wonder why
> not pass the iocb and the iov_iter instead of pos and the iov_iter?

The original user of generic_atomic_write_valid() 
[blkdev_dio_unaligned() or blkdev_dio_invalid() with the rename] used 
these same args, so I just went with that.

> And can these be collapsed into a single generic_atomic_write_checks()
> function?

bdev file operations would then need to use 
generic_atomic_write_valid_size(), and there is no unit_min and unit_max 
size there, apart from bdev awu min and max. And if I checked them, we 
would be duplicating checks (of awu min and max) in the block layer.

Cheers,
John