Re: [fuse-devel] [PATCH 4/6] fs/fuse: support compiling out splice

[Greg KH]

On Mon, Nov 24, 2014 at 08:05:10AM -0800, Josh Triplett wrote:
> On Mon, Nov 24, 2014 at 10:49:31AM +0100, Pieter Smith wrote:
> > On Sun, Nov 23, 2014 at 03:23:02PM -0800, Josh Triplett wrote:
> > > On Sun, Nov 23, 2014 at 11:29:08PM +0100, Richard Weinberger wrote:
> > > > On Sun, Nov 23, 2014 at 3:20 PM, Pieter Smith <pieter@xxxxxxxxxx> wrote:
> > > > > To implement splice support, fs/fuse makes use of nosteal_pipe_buf_ops. This
> > > > > struct is exported by fs/splice. The goal of the larger patch set is to
> > > > > completely compile out fs/splice, so uses of the exported struct need to be
> > > > > compiled out along with fs/splice.
> > > > >
> > > > > This patch therefore compiles out splice support in fs/fuse when
> > > > > CONFIG_SYSCALL_SPLICE is undefined.
> > > > >
> > > > > Signed-off-by: Pieter Smith <pieter@xxxxxxxxxx>
> > > > > ---
> > > > >  fs/fuse/dev.c      | 4 ++--
> > > > >  include/linux/fs.h | 6 ++++++
> > > > >  2 files changed, 8 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> > > > > index ca88731..f8f92a4 100644
> > > > > --- a/fs/fuse/dev.c
> > > > > +++ b/fs/fuse/dev.c
> > > > > @@ -1291,7 +1291,7 @@ static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
> > > > >         return fuse_dev_do_read(fc, file, &cs, iov_length(iov, nr_segs));
> > > > >  }
> > > > >
> > > > > -static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
> > > > > +static ssize_t __maybe_unused fuse_dev_splice_read(struct file *in, loff_t *ppos,
> > > > >                                     struct pipe_inode_info *pipe,
> > > > >                                     size_t len, unsigned int flags)
> > > > >  {
> > > > > @@ -2144,7 +2144,7 @@ const struct file_operations fuse_dev_operations = {
> > > > >         .llseek         = no_llseek,
> > > > >         .read           = do_sync_read,
> > > > >         .aio_read       = fuse_dev_read,
> > > > > -       .splice_read    = fuse_dev_splice_read,
> > > > > +       .splice_read    = __splice_p(fuse_dev_splice_read),
> > > > >         .write          = do_sync_write,
> > > > >         .aio_write      = fuse_dev_write,
> > > > >         .splice_write   = fuse_dev_splice_write,
> > > > > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > > > > index a957d43..04c0975 100644
> > > > > --- a/include/linux/fs.h
> > > > > +++ b/include/linux/fs.h
> > > > > @@ -2443,6 +2443,12 @@ extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end,
> > > > >                         int datasync);
> > > > >  extern void block_sync_page(struct page *page);
> > > > >
> > > > > +#ifdef CONFIG_SYSCALL_SPLICE
> > > > > +#define __splice_p(x) x
> > > > > +#else
> > > > > +#define __splice_p(x) NULL
> > > > > +#endif
> > > > > +
> > > > 
> > > > This needs to go into a different patch.
> > > > One logical change per patch please. :-)
> > > 
> > > Easy enough to merge this one into the patch introducing
> > > CONFIG_SYSCALL_SPLICE, then.
> > > 
> > > - Josh Triplett
> > 
> > The patch introducing CONFIG_SYSCALL_SPLICE (PATCH 3) only compiles out the
> > syscalls. PATCH 6 on the other hand, compiles out fs/splice.c. This patch
> > allows fs/fuse to be compiled when fs/splice.c is compiled out. If I am to
> > squash it, it would be logical to include it in PATCH 6, not 3.
> 
> The suggestion wasn't to move the fs/fuse/dev.c bits; those should
> definitely stay in this patch.  The suggestion was just to move the bit
> of the patch defining __splice_p from this patch to patch 3.  (Note that
> you need to define it before you use it, so it can't go in patch 6.)

I would, again, argue that stuff like __splice_p() not be implemented at
all please.  It will only cause a huge proliferation of stuff like this
that will not make any sense, and only cause a trivial, if any, amount
of code savings.

I thought you were going to not do this type of thing until you got the
gcc optimizer working for function callbacks.

Again, don't do this please.

thanks,

greg k-h
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