On Fri, Dec 04, 2015 at 10:49:24AM -0500, Anna Schumaker wrote:
> On 12/04/2015 10:45 AM, J. Bruce Fields wrote:
> > On Thu, Dec 03, 2015 at 03:55:35PM -0500, Anna Schumaker wrote:
> >> @@ -498,6 +499,22 @@ __be32 nfsd4_set_nfs4_label(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >> }
> >> #endif
> >>
> >> +ssize_t nfsd_copy_range(struct file *src, u64 src_pos,
> >> + struct file *dst, u64 dst_pos,
> >> + u64 count)
> >> +{
> >> + ssize_t bytes;
> >> + u64 limit = 0x10000000;
> >
> > Why that value? Could I get a comment here?
>
> Whoops! I had a comment there at one point, but I must have deleted it :(. That value is to cap copies to 256MB.
Could you include some justification for the choice of that particular
value?
> >> + if (count > limit)
> >> + count = limit;
> >> +
> >> + bytes = vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
> >
> > Sorry, I lost track of the copy discussions: does this only work on
> > filesystems with special support, or does it fall back on doing the copy
> > by hand? Which filesystems (of the exportable filesystems) support
> > this?
>
> The system call falls back on doing the copy by hand if there is no filesystem acceleration.
Is this practical? It means a huge range in possible latency of the
single COPY call depending on filesystem.
I guess I can live with it and we can see if people run into problems in
practice. But let's make sure this is documented.
--b.
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