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examples: add an example for external kernels
Add an example for loading an external kernel, initramfs and custom kernel command line. Signed-off-by: Sergio Lopez <slp@redhat.com>
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‎examples/Makefile

+8-2
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@ ROOTFS_DIR = rootfs_$(ROOTFS_DISTRO)
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.PHONY: clean rootfs
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EXAMPLES := chroot_vm
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EXAMPLES := chroot_vm external_kernel
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ifeq ($(SEV),1)
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EXAMPLES := launch-tee
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endif
@@ -36,6 +36,12 @@ ifeq ($(OS),Darwin)
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codesign --entitlements chroot_vm.entitlements --force -s - $@
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endif
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external_kernel: external_kernel.c
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gcc -o $@ $< $(CFLAGS) $(LDFLAGS_$(ARCH)_$(OS))
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ifeq ($(OS),Darwin)
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codesign --entitlements chroot_vm.entitlements --force -s - $@
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endif
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# Build the rootfs to be used with chroot_vm.
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rootfs:
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mkdir -p $(ROOTFS_DIR)
@@ -44,4 +50,4 @@ rootfs:
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podman rm libkrun_chroot_vm
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clean:
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rm -rf chroot_vm $(ROOTFS_DIR) launch-tee boot_efi
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rm -rf chroot_vm $(ROOTFS_DIR) launch-tee boot_efi external_kernel

‎examples/external_kernel.c

+321
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,321 @@
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/*
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* This is an example implementing chroot-like functionality with libkrun.
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*
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* It executes the requested command (relative to NEWROOT) inside a fresh
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* Virtual Machine created and managed by libkrun.
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*/
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/socket.h>
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#include <sys/un.h>
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#include <unistd.h>
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#include <libkrun.h>
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#include <getopt.h>
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#include <stdbool.h>
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#include <assert.h>
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#include <pthread.h>
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#define MAX_ARGS_LEN 4096
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#ifndef MAX_PATH
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#define MAX_PATH 4096
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#endif
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enum net_mode
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{
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NET_MODE_PASST = 0,
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NET_MODE_TSI,
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};
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#if defined(__x86_64__)
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#define KERNEL_FORMAT KRUN_KERNEL_FORMAT_ELF
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#else
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#define KERNEL_FORMAT KRUN_KERNEL_FORMAT_RAW
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#endif
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static void print_help(char *const name)
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{
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fprintf(stderr,
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"Usage: %s [OPTIONS] KERNEL\n"
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"OPTIONS: \n"
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" -b --boot-disk Path to a boot disk in raw format\n"
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" -c --kernel-cmdline Kernel command line\n"
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" -d --data-disk Path to a data disk in raw format\n"
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" -h --help Show help\n"
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" -i --initrd Path to initramfs\n"
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" --net=NET_MODE Set network mode\n"
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" --passt-socket=PATH Connect to passt socket at PATH"
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"\n"
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"NET_MODE can be either TSI (default) or PASST\n"
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"\n"
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#if defined(__x86_64__)
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"KERNEL: path to the kernel image in ELF format\n",
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#else
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"KERNEL: path to the kernel image in RAW format\n",
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#endif
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name);
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}
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static const struct option long_options[] = {
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{"boot-disk", required_argument, NULL, 'b'},
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{"kernel-cmdline", required_argument, NULL, 'c'},
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{"data-disk", required_argument, NULL, 'd'},
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{"initrd-path", required_argument, NULL, 'i'},
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{"help", no_argument, NULL, 'h'},
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{"passt-socket", required_argument, NULL, 'P'},
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{NULL, 0, NULL, 0}};
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struct cmdline
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{
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bool show_help;
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enum net_mode net_mode;
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char const *boot_disk;
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char const *data_disk;
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char const *passt_socket_path;
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char const *kernel_path;
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char const *kernel_cmdline;
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char const *initrd_path;
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};
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bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
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{
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assert(cmdline != NULL);
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// set the defaults
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*cmdline = (struct cmdline){
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.show_help = false,
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.net_mode = NET_MODE_TSI,
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.passt_socket_path = "/tmp/network.sock",
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.boot_disk = NULL,
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.data_disk = NULL,
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.kernel_path = NULL,
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.kernel_cmdline = NULL,
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.initrd_path = NULL,
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};
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int option_index = 0;
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int c;
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// the '+' in optstring is a GNU extension that disables permutating argv
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while ((c = getopt_long(argc, argv, "+hb:c:d:i:", long_options, &option_index)) != -1)
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{
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switch (c)
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{
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case 'b':
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cmdline->boot_disk = optarg;
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break;
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case 'c':
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cmdline->kernel_cmdline = optarg;
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break;
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case 'd':
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cmdline->data_disk = optarg;
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break;
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case 'h':
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cmdline->show_help = true;
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return true;
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case 'i':
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cmdline->initrd_path = optarg;
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break;
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case 'P':
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cmdline->passt_socket_path = optarg;
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break;
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case '?':
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return false;
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default:
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fprintf(stderr, "internal argument parsing error (returned character code 0x%x)\n", c);
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return false;
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}
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}
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if (optind <= argc - 1)
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{
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cmdline->kernel_path = argv[optind];
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return true;
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}
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if (optind == argc)
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{
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fprintf(stderr, "Missing KERNEL argument\n");
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}
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return false;
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}
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int connect_to_passt(char *socket_path)
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{
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struct sockaddr_un addr;
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int socket_fd = socket(AF_UNIX, SOCK_STREAM, 0);
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if (socket_fd < 0)
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{
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perror("Failed to create passt socket fd");
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return -1;
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}
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memset(&addr, 0, sizeof(addr));
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addr.sun_family = AF_UNIX;
157+
strncpy(addr.sun_path, socket_path, sizeof(addr.sun_path) - 1);
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if (connect(socket_fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0)
160+
{
161+
perror("Failed to bind passt socket");
162+
return -1;
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}
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165+
return socket_fd;
166+
}
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int start_passt()
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{
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int socket_fds[2];
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const int PARENT = 0;
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const int CHILD = 1;
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if (socketpair(AF_UNIX, SOCK_STREAM, 0, socket_fds) < 0)
175+
{
176+
perror("Failed to create passt socket fd");
177+
return -1;
178+
}
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180+
int pid = fork();
181+
if (pid < 0)
182+
{
183+
perror("fork");
184+
return -1;
185+
}
186+
187+
if (pid == 0)
188+
{ // child
189+
if (close(socket_fds[PARENT]) < 0)
190+
{
191+
perror("close PARENT");
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}
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194+
char fd_as_str[16];
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snprintf(fd_as_str, sizeof(fd_as_str), "%d", socket_fds[CHILD]);
196+
197+
printf("passing fd %s to passt", fd_as_str);
198+
199+
if (execlp("passt", "passt", "-f", "--fd", fd_as_str, NULL) < 0)
200+
{
201+
perror("execlp");
202+
return -1;
203+
}
204+
}
205+
else
206+
{ // parent
207+
if (close(socket_fds[CHILD]) < 0)
208+
{
209+
perror("close CHILD");
210+
}
211+
212+
return socket_fds[PARENT];
213+
}
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}
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int main(int argc, char *const argv[])
217+
{
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int ctx_id;
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int err;
220+
pthread_t thread;
221+
struct cmdline cmdline;
222+
223+
if (!parse_cmdline(argc, argv, &cmdline))
224+
{
225+
putchar('\n');
226+
print_help(argv[0]);
227+
return -1;
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}
229+
230+
if (cmdline.show_help)
231+
{
232+
print_help(argv[0]);
233+
return 0;
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}
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// Set the log level to "off".
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err = krun_set_log_level(0);
238+
if (err)
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{
240+
errno = -err;
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perror("Error configuring log level");
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return -1;
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}
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// Create the configuration context.
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ctx_id = krun_create_ctx();
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if (ctx_id < 0)
248+
{
249+
errno = -ctx_id;
250+
perror("Error creating configuration context");
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return -1;
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}
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// Configure the number of vCPUs (2) and the amount of RAM (1024 MiB).
255+
if (err = krun_set_vm_config(ctx_id, 2, 2048))
256+
{
257+
errno = -err;
258+
perror("Error configuring the number of vCPUs and/or the amount of RAM");
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return -1;
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}
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if (cmdline.boot_disk)
263+
{
264+
if (err = krun_add_disk(ctx_id, "boot", cmdline.boot_disk, 0))
265+
{
266+
errno = -err,
267+
perror("Error configuring boot disk");
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return -1;
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}
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}
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if (cmdline.data_disk)
272+
{
273+
if (err = krun_add_disk(ctx_id, "data", cmdline.data_disk, 0))
274+
{
275+
errno = -err,
276+
perror("Error configuring data disk");
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return -1;
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}
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}
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if (cmdline.net_mode == NET_MODE_PASST)
282+
{
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int passt_fd = cmdline.passt_socket_path ? connect_to_passt(cmdline.passt_socket_path) : start_passt();
284+
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if (passt_fd < 0)
286+
{
287+
return -1;
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}
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if (err = krun_set_passt_fd(ctx_id, passt_fd))
291+
{
292+
errno = -err;
293+
perror("Error configuring net mode");
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return -1;
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}
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}
297+
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fprintf(stderr, "kernel_path: %s\n", cmdline.kernel_path);
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fprintf(stderr, "kernel_cmdline: %s\n", cmdline.kernel_cmdline);
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fflush(stderr);
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if (err = krun_set_kernel(ctx_id, cmdline.kernel_path, KERNEL_FORMAT,
303+
cmdline.initrd_path, cmdline.kernel_cmdline))
304+
{
305+
errno = -err;
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perror("Error configuring kernel");
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return -1;
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}
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// Start and enter the microVM. Unless there is some error while creating the microVM
311+
// this function never returns.
312+
if (err = krun_start_enter(ctx_id))
313+
{
314+
errno = -err;
315+
perror("Error creating the microVM");
316+
return -1;
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}
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// Not reached.
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return 0;
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}

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