On Thu, May 31 2007, Christoph Hellwig wrote:
> On Thu, May 31, 2007 at 12:33:16PM +0200, Jens Axboe wrote:
> > - nfds: The ->rq_sendfile_ok optimization is gone for now. I can't
> > determine the value of it, but I'm assuming it's there for a reason.
> > Any chance this can be converted to splice, or use something else than
> > ->sendfile()? CC'ed Neil.
>
> sendfile useage in nfsd avoids a data copy and allows to use checksum
> offloading. it's quite important for nfs server workloads.
OK, I hope Neil can provide some input on how to convert it. Of course
I'm just fishing for Neil to actually do that work :-)
> > Apart from that, it was mostly straight forward. Almost everybody uses
> > generic_file_sendfile(), which makes the conversion easy. I changed loop
> > to use do_generic_file_read() instead of sendfile, it works for me...
>
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index 5526ead..92bac14 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -435,16 +435,24 @@ do_lo_receive(struct loop_device *lo,
> > {
> > struct lo_read_data cookie;
> > struct file *file;
> > - int retval;
> > + read_descriptor_t desc;
> > +
> > + desc.written = 0;
> > + desc.count = bvec->bv_len;
> > + desc.arg.data = &cookie;
> > + desc.error = 0;
> >
> > cookie.lo = lo;
> > cookie.page = bvec->bv_page;
> > cookie.offset = bvec->bv_offset;
> > cookie.bsize = bsize;
> > file = lo->lo_backing_file;
> > - retval = file->f_op->sendfile(file, &pos, bvec->bv_len,
> > - lo_read_actor, &cookie);
> > - return (retval < 0)? retval: 0;
> > +
> > + do_generic_file_read(file, &pos, &desc, lo_read_actor);
>
> This change is wrong. loop or any existing user of ->sendfile absolutely
> needs to go through a file operations vector so that file-system specific
> actions such as locking are performed. This is required at least for the
> clustered filesystems and XFS. The right way to implement this is
> via do_splice_direct or something similar.
>
> do_generic_file_read is only a library function for filesystem use
> and should never be called directly.
I'll convert it to do_splice_direct(), thanks.
--
Jens Axboe
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