[bpf-next,V1] enable virtFS(9p virtio) for sharing directory on VM to optimize debugging

Commit Message

Lin Yikai Aug. 29, 2024, 12:25 p.m. UTC

[Problem]
Sometimes, we have only x86_64 server for compiling BPF with target ARCH of arm64.
Therefore, the only way to debug bpf is using cross-compile and qemu.

Unfortunately, debugging online on VM is very inconvenient, when test_progs fails.
Such as:
1. We are unable to directly replace old test object
and still need to quit VM and restart, which consumes valuable time.
2. We also want to share other tools or binaries online for execution on the VM,
which is not supported by VM.

[Optimization]
I noitce that CONFIG_9P_FS is enabled in "config.vm",
so virtFS (9p virtio) is available on VM.

To achieve it, I add a new init file on qemu,
which only exists when '-v' option is appended.
  root@(none):/# cat /etc/rcS.d/S20-testDebug
  #!/bin/sh
  set -x
  rm -rf /mnt/shared
  mkdir -p /mnt/shared
  /bin/mount -t 9p -o trans=virtio,version=9p2000.L host0 /mnt/shared

[Usage]
Append the option '-v' to enable it.
For instance:
  LDLIBS=-static ./vmtest.sh -v -s -- ./test_progs -t d_path

This will share the directory
between VM's "/mnt/shared" with host's *${OUTPUT_DIR}/${MOUNT_DIR}/shared*.

On host:
  $ mv ./test_progs ~/workplace/bpf/arm64/.bpf_selftests/mnt/shared/
On VM(you can directly move it into /root/bpf):
  root@(none):/# ls /mnt/shared/
 test_progs


Signed-off-by: Lin Yikai <[e-mail]>
---
 tools/testing/selftests/bpf/vmtest.sh | 75 ++++++++++++++++++++++++++-
 1 file changed, 73 insertions(+), 2 deletions(-)

Patch

diff --git a/tools/testing/selftests/bpf/vmtest.sh b/tools/testing/selftests/bpf/vmtest.sh
index c7461ed496ab..82afadde50da 100755
--- a/tools/testing/selftests/bpf/vmtest.sh
+++ b/tools/testing/selftests/bpf/vmtest.sh
@@ -70,10 +70,15 @@  LOG_FILE_BASE="$(date +"bpf_selftests.%Y-%m-%d_%H-%M-%S")"
 LOG_FILE="${LOG_FILE_BASE}.log"
 EXIT_STATUS_FILE="${LOG_FILE_BASE}.exit_status"
 
+DEBUG_CMD_INIT=""
+DEBUG_FILE_INIT="S20-testDebug"
+QEMU_FLAG_VIRTFS=""
+
+
 usage()
 {
 	cat <<EOF
-Usage: $0 [-i] [-s] [-d <output_dir>] -- [<command>]
+Usage: $0 [-i] [-s] [-v] [-d <output_dir>] -- [<command>]
 
 <command> is the command you would normally run when you are in
 tools/testing/selftests/bpf. e.g:
@@ -101,6 +106,8 @@  Options:
 	-s)		Instead of powering off the VM, start an interactive
 			shell. If <command> is specified, the shell runs after
 			the command finishes executing
+	-v)		enable virtFS (9p virtio) for sharing directory
+			of "/mnt/shared" on the VM
 EOF
 }
 
@@ -275,6 +282,7 @@  EOF
 		-serial mon:stdio \
 		"${QEMU_FLAGS[@]}" \
 		-enable-kvm \
+		${QEMU_FLAG_VIRTFS} \
 		-m 4G \
 		-drive file="${rootfs_img}",format=raw,index=1,media=disk,if=virtio,cache=none \
 		-kernel "${kernel_bzimage}" \
@@ -354,6 +362,60 @@  catch()
 	exit ${exit_code}
 }
 
+update_debug_init()
+{
+	#You can do something else just for debuging on qemu.
+	#The init script will be reset every time before vm running on host,
+	#and be executed on qemu before test_progs.
+	local init_script_dir="${OUTPUT_DIR}/${MOUNT_DIR}/etc/rcS.d"
+	local init_script_file="${init_script_dir}/${DEBUG_FILE_INIT}"
+
+	mount_image
+	if [[ "${DEBUG_CMD_INIT}" == "" ]]; then
+		sudo rm -rf ${init_script_file}
+		unmount_image
+		return
+	fi
+
+	if [[ ! -d "${init_script_dir}" ]]; then
+		cat <<EOF
+Could not find ${init_script_dir} in the mounted image.
+This likely indicates a bad or not default rootfs image,
+You need to change debug init manually
+according to the actual situation of the rootfs image.
+EOF
+		unmount_image
+		exit 1
+	fi
+
+	sudo bash -c "cat > ${init_script_file}" <<EOF
+#!/bin/sh
+set -x
+${DEBUG_CMD_INIT}
+EOF
+	sudo chmod 755 "${init_script_file}"
+	unmount_image
+}
+
+#Establish shared dir access by 9p virtfs
+#between "/mnt/shared" on qemu with *${OUTPUT_DIR}/${MOUNT_DIR}/shared* on local host.
+debug_by_virtfs_shared()
+{
+	local qemu_shared_dir="/mnt/shared"
+	local host_shared_dir="${OUTPUT_DIR}/${MOUNT_DIR}/shared"
+
+	#append virtfs shared flag for qemu
+	local flag="-virtfs local,mount_tag=host0,security_model=passthrough,id=host0,path=${host_shared_dir}"
+	mkdir -p "${host_shared_dir}"
+	QEMU_FLAG_VIRTFS="${QEMU_FLAG_VIRTFS} ${flag}"
+
+	#append mount cmd into init
+	DEBUG_CMD_INIT="${DEBUG_CMD_INIT}\
+rm -rf ${qemu_shared_dir}
+mkdir -p ${qemu_shared_dir}
+/bin/mount -t 9p -o trans=virtio,version=9p2000.L host0 ${qemu_shared_dir}"
+}
+
 main()
 {
 	local script_dir="$(cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
@@ -365,8 +427,9 @@  main()
 	local update_image="no"
 	local exit_command="poweroff -f"
 	local debug_shell="no"
+	local enable_virtfs_shared="no"
 
-	while getopts ':hskid:j:' opt; do
+	while getopts ':vhskid:j:' opt; do
 		case ${opt} in
 		i)
 			update_image="yes"
@@ -382,6 +445,9 @@  main()
 			debug_shell="yes"
 			exit_command="bash"
 			;;
+		v)
+			enable_virtfs_shared="yes"
+			;;
 		h)
 			usage
 			exit 0
@@ -449,6 +515,11 @@  main()
 		create_vm_image
 	fi
 
+	if [[ "${enable_virtfs_shared}" == "yes" ]]; then
+		debug_by_virtfs_shared
+	fi
+	update_debug_init
+
 	update_selftests "${kernel_checkout}" "${make_command}"
 	update_init_script "${command}" "${exit_command}"
 	run_vm "${kernel_bzimage}"