Re: [Xen-devel] [PATCH v6 0/3] libxenvchan: interdomain communications library

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On Fri, Sep 30, 2011 at 10:40:11AM -0400, Daniel De Graaf wrote:
> >>
> >> 2011/9/23 Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> >>
> >>> Changes since v5:
> >>>  - Unify gntdev osdep interface
> >>>  - Eliminate notify_result and revert mapping if notify ioctl fails
> >>>  - Rename functions and structures to libxenvchan
> >>>  - Use application-specified xenstore path for ring/event data
> >>>  - Enforce maximum ring size of 2^20 bytes on client
> >>>  - Change to LGPL 2.1
> >>>
> >>> [PATCH 1/3] libxc: add xc_gnttab_map_grant_ref_notify
> >>> [PATCH 2/3] libxc: add xc_gntshr_* functions
> >>> [PATCH 3/3] libvchan: interdomain communications library
> >>>
<snip>
> This library depends on gntdev for the client and gntalloc for the server;
> these were merged in 2.6.39. The client can be used with 2.6.32.x kernels
> however it is not possible to detect when a peer crashes or exits without
> calling libxenvchan_close() on that kernel.

I'm trying this with your most recent dom0 patches all included, and
xen-unstable. In order to get decent performance, I tried the vchan-node
examples with a cranked up buffer size, which fails immediately on 64-bit
VMs.  This below patch fixes the xc_gntshr_share_pages call (which sets
notify_offset to -1 and without this bounds check will send a big offset
to the unmap notify ioctl).

With this, communication does work with the big buffers, but it never
frees them, and so I can get an ENOSPACE error by calling vchan-node a few
times. What's the intended cleanup path for the grants in normal use of
the vchan library? Something's holding onto them, but I don't have a
serial console on my current laptop in order to drop into Xen's serial and
find out more.

diff -r 614e9f371209 tools/libxc/xc_linux_osdep.c
--- a/tools/libxc/xc_linux_osdep.c      Thu Nov 24 18:53:09 2011 +0000
+++ b/tools/libxc/xc_linux_osdep.c      Thu Nov 24 20:00:21 2011 +0000
@@ -709,7 +709,7 @@
 
     notify.index = gref_info->index;
     notify.action = 0;
-    if (notify_offset >= 0) {
+    if (notify_offset >= 0 && notify_offset < XC_PAGE_SIZE * count) {
         notify.index += notify_offset;
         notify.action |= UNMAP_NOTIFY_CLEAR_BYTE;
     }


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