9p/net: Fix zero-copy path in the 9p virtio transport

The zero-copy optimization when reading or writing large chunks of data
is quite useful.  However, the 9p messages created through the zero-copy
write path have an incorrect message size: it should be the size of the
header + size of the data being written but instead it's just the size
of the header.

This only works if the server ignores the size field of the message and
otherwise breaks the framing of the protocol. Fix this by re-writing the
message size field with the correct value.

Tested by running `dd if=/dev/zero of=out bs=4k count=1` inside a
virtio-9p mount.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Chirantan Ekbote <[email protected]>
Reviewed-by: Greg Kurz <[email protected]>
Tested-by: Greg Kurz <[email protected]>
Cc: Dylan Reid <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: [email protected]
Signed-off-by: Dominique Martinet <[email protected]>

0 files changed, 0 insertions, 0 deletions