Re: [PATCH 5/7] add llseek_nowait support for xfs

[Hao Xu <hao.xu@xxxxxxxxx>]

On 7/27/23 06:14, Dave Chinner wrote:
> On Wed, Jul 26, 2023 at 06:26:01PM +0800, Hao Xu wrote:
> > From: Hao Xu <howeyxu@xxxxxxxxxxx>
> >
> > Add llseek_nowait() operation for xfs, it acts just like llseek(). The
> > thing different is it delivers nowait parameter to iomap layer.
> >
> > Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
> > ---
> >   fs/xfs/xfs_file.c | 29 +++++++++++++++++++++++++++--
> >   1 file changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 73adc0aee2ff..cba82264221d 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -1257,10 +1257,11 @@ xfs_file_readdir(
> >   }
> >   
> >   STATIC loff_t
> > -xfs_file_llseek(
> > +__xfs_file_llseek(
> >   	struct file	*file,
> >   	loff_t		offset,
> > -	int		whence)
> > +	int		whence,
> > +	bool		nowait)
> >   {
> >   	struct inode		*inode = file->f_mapping->host;
> >   
> > @@ -1282,6 +1283,28 @@ xfs_file_llseek(
> >   	return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
> >   }
> >   
> > +STATIC loff_t
> > +xfs_file_llseek(
> > +	struct file	*file,
> > +	loff_t		offset,
> > +	int		whence)
> > +{
> > +	return __xfs_file_llseek(file, offset, whence, false);
> > +}
> > +
> > +STATIC loff_t
> > +xfs_file_llseek_nowait(
> > +	struct file	*file,
> > +	loff_t		offset,
> > +	int		whence,
> > +	bool		nowait)
> > +{
> > +	if (file->f_op == &xfs_file_operations)
> > +		return __xfs_file_llseek(file, offset, whence, nowait);
> > +	else
> > +		return generic_file_llseek(file, offset, whence);
> > +}
> > +
> >   #ifdef CONFIG_FS_DAX
> >   static inline vm_fault_t
> >   xfs_dax_fault(
> > @@ -1442,6 +1465,7 @@ xfs_file_mmap(
> >   
> >   const struct file_operations xfs_file_operations = {
> >   	.llseek		= xfs_file_llseek,
> > +	.llseek_nowait	= xfs_file_llseek_nowait,
> >   	.read_iter	= xfs_file_read_iter,
> >   	.write_iter	= xfs_file_write_iter,
> >   	.splice_read	= xfs_file_splice_read,
> > @@ -1467,6 +1491,7 @@ const struct file_operations xfs_dir_file_operations = {
> >   	.read		= generic_read_dir,
> >   	.iterate_shared	= xfs_file_readdir,
> >   	.llseek		= generic_file_llseek,
> > +	.llseek_nowait	= xfs_file_llseek_nowait,
> >   	.unlocked_ioctl	= xfs_file_ioctl,
> >   #ifdef CONFIG_COMPAT
> >   	.compat_ioctl	= xfs_file_compat_ioctl,
>
> This is pretty nasty. It would be far better just to change the
> .llseek method than to inflict this on every filesystem for the
> forseeable future.
>
> Not that I'm a fan of passing "nowait" booleans all through the file
> operations methods - that way lies madness. We use a control
> structure for the IO path operations (kiocb) to hold per-call
> context information, perhaps we need something similar for these
> other methods that people are wanting to hook up to io_uring (e.g.
> readdir) so taht we don't have to play whack-a-mole with every new
> io_uring method that people want and then end up with a different
> nowait solution for every method.
>
> -Dave.

whack-a-mole is exactly what I thought when I tried to find a place to
hold that...I'll think about it in next version, a generic structure for
io_uring is good I believe. I'll update this patchset after the getdents
stuff are merged.

Thanks,
Hao