On 27/10/15 17:10, Wei Liu wrote: > When oxenstored wrote to the ring, it wrote a chunk of contiguous data. > Originally when it tried to write across ring boundary, it returned a > short-write when there is still room. That led to stalling mini-os's > xenstore thread at times. > > Fix this by calling write function for a second time when the first > write completes partially. > > Signed-off-by: Samuel Thibault <samuel.thiba...@ens-lyon.org> > Signed-off-by: Wei Liu <wei.l...@citrix.com> > --- > Cc: David Scott <d...@recoil.org> > Cc: Ian Campbell <ian.campb...@citrix.com> > Cc: Ian Jackson <ian.jack...@eu.citrix.com> > > Ian, backport candidate for as far as you can manage. > --- > tools/ocaml/libs/xb/xb.ml | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/tools/ocaml/libs/xb/xb.ml b/tools/ocaml/libs/xb/xb.ml > index 50944b5..0730d13 100644 > --- a/tools/ocaml/libs/xb/xb.ml > +++ b/tools/ocaml/libs/xb/xb.ml > @@ -91,10 +91,12 @@ let write_fd back con s len = > Unix.write back.fd s 0 len > > let write_mmap back con s len = > - let ws = Xs_ring.write back.mmap s len in > - if ws > 0 then > + let ws = ref (Xs_ring.write back.mmap s len) in > + if !ws < len then > + ws := !ws + Xs_ring.write back.mmap (String.sub s !ws (len - > !ws)) (len - !ws);
This is surely a TOCTOU, as the second attempted write could return short as well. The correct behaviour would be for Xs_ring.write to return the actual number of bytes it put into the ring, even if this is shorter than len. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
