virtio: Implement the 9P device

Implement a new virtio_9p device to be used for sharing directories with
the VM.

BUG=chromium:703939
TEST=mount inside a VM and run `bonnie++ -r 256`
Append the shared directory to the crosvm command line:
--shared-dir /path/to/dir:test_9p
Then mount in the guest:
mkdir /tmp/9p
mount -t 9p -o trans=virtio test_9p /tmp/9p -oversion=9p2000.L
Or for a 9p root:
run --shared-dir /mnt/vm_root:/dev/root -p 'root=/dev/root ro rootflags=ro,trans=virtio,version=9p2000.L,cache=loose rootfstype=9p' vmlinux.bin

CQ-DEPEND=CL:1065170

Change-Id: I41fc21306ab5fa318a271f172d7057b767b29f31
Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1065173
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Dylan Reid <dgreid@chromium.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/devices/src/virtio/mod.rs b/devices/src/virtio/mod.rs
index 8e8e4b6..91a2c23 100644
--- a/devices/src/virtio/mod.rs
+++ b/devices/src/virtio/mod.rs
@@ -12,6 +12,7 @@ mod rng;
 mod net;
 #[cfg(feature = "gpu")]
 mod gpu;
+mod p9;
 mod wl;
 
 pub mod vhost;
@@ -24,6 +25,7 @@ pub use self::rng::*;
 pub use self::net::*;
 #[cfg(feature = "gpu")]
 pub use self::gpu::*;
+pub use self::p9::*;
 pub use self::wl::*;
 
 const DEVICE_ACKNOWLEDGE: u32 = 0x01;
@@ -39,6 +41,7 @@ const TYPE_RNG: u32 = 4;
 const TYPE_BALLOON: u32 = 5;
 #[allow(dead_code)]
 const TYPE_GPU: u32 = 16;
+const TYPE_9P: u32 = 9;
 const TYPE_VSOCK: u32 = 19;
 const TYPE_WL: u32 = 30;