[lxc-devel] [PATCH] lxcapi_restore shouldn't steal the calling process
Tycho Andersen
tycho.andersen at canonical.com
Thu Mar 26 14:52:15 UTC 2015
On Wed, Mar 25, 2015 at 11:05:23AM -0600, Tycho Andersen wrote:
> Previously, lxcapi_restore used the calling process as the lxc monitor process
> (and just never returned), requiring users to fork before calling it. This, of
> course, would cause problems for things like LXD, which can't fork.
>
> Now, restore() forks the monitor as a child of the process that calls it. Users
> who want to daemonize the restore process need to fork themselves.
> lxc-checkpoint has been updated to reflect this behavior change.
>
> Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> ---
> src/lxc/lxc_checkpoint.c | 48 +++++++++++++++------
> src/lxc/lxccontainer.c | 109 ++++++++++++++++++++++++++++++++++-------------
> 2 files changed, 114 insertions(+), 43 deletions(-)
>
> diff --git a/src/lxc/lxc_checkpoint.c b/src/lxc/lxc_checkpoint.c
> index cfa08fc..2e76c2e 100644
> --- a/src/lxc/lxc_checkpoint.c
> +++ b/src/lxc/lxc_checkpoint.c
> @@ -20,6 +20,8 @@
> #include <stdio.h>
> #include <errno.h>
> #include <unistd.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
>
> #include <lxc/lxccontainer.h>
>
> @@ -27,6 +29,7 @@
> #include "config.h"
> #include "lxc.h"
> #include "arguments.h"
> +#include "utils.h"
>
> static char *checkpoint_dir = NULL;
> static bool stop = false;
> @@ -139,36 +142,53 @@ bool checkpoint(struct lxc_container *c)
> return true;
> }
>
> -bool restore(struct lxc_container *c)
> +bool restore_finalize(struct lxc_container *c)
> {
> - pid_t pid = 0;
> - bool ret = true;
> + bool ret = c->restore(c, checkpoint_dir, verbose);
> + if (!ret) {
> + fprintf(stderr, "Restoring %s failed.\n", my_args.name);
> + }
>
> + lxc_container_put(c);
> + return ret;
> +}
> +
> +bool restore(struct lxc_container *c)
> +{
> if (c->is_running(c)) {
> fprintf(stderr, "%s is running, not restoring.\n", my_args.name);
> lxc_container_put(c);
> return false;
> }
>
> - if (my_args.daemonize)
> + if (my_args.daemonize) {
> + pid_t pid;
> +
> pid = fork();
> + if (pid < 0) {
> + perror("fork");
> + return false;
> + }
>
> - if (pid == 0) {
> - if (my_args.daemonize) {
> + if (pid == 0) {
> close(0);
> close(1);
> - }
>
> - ret = c->restore(c, checkpoint_dir, verbose);
> -
> - if (!ret) {
> - fprintf(stderr, "Restoring %s failed.\n", my_args.name);
> + exit(!restore_finalize(c));
> + } else {
> + return wait_for_pid(pid) == 0;
> }
> - }
> + } else {
> + int status;
>
> - lxc_container_put(c);
> + if (!restore_finalize(c))
> + return false;
>
> - return ret;
> + if (waitpid(-1, &status, 0) < 0)
> + return false;
> +
> + return WIFEXITED(status) && WEXITSTATUS(status) == 0;
> + }
> }
>
> int main(int argc, char *argv[])
> diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> index 4422f4a..ecea7bf 100644
> --- a/src/lxc/lxccontainer.c
> +++ b/src/lxc/lxccontainer.c
> @@ -3853,28 +3853,20 @@ out_unlock:
> return !has_error;
> }
>
> -static bool lxcapi_restore(struct lxc_container *c, char *directory, bool verbose)
> +// do_restore never returns, the calling process is used as the
> +// monitor process. do_restore calls exit() if it fails.
> +static void do_restore(struct lxc_container *c, int pipe, char *directory, bool verbose)
> {
> pid_t pid;
> - struct lxc_rootfs *rootfs;
> char pidfile[L_tmpnam];
> struct lxc_handler *handler;
> - bool has_error = true;
> -
> - if (!criu_ok(c))
> - return false;
> -
> - if (geteuid()) {
> - ERROR("Must be root to restore\n");
> - return false;
> - }
>
> if (!tmpnam(pidfile))
> - return false;
> + exit(1);
>
> handler = lxc_init(c->name, c->lxc_conf, c->config_path);
> if (!handler)
> - return false;
> + exit(1);
>
> if (!cgroup_init(handler)) {
> ERROR("failed initing cgroups");
> @@ -3897,9 +3889,10 @@ static bool lxcapi_restore(struct lxc_container *c, char *directory, bool verbos
>
> if (pid == 0) {
> struct criu_opts os;
> + struct lxc_rootfs *rootfs;
>
> if (unshare(CLONE_NEWNS))
> - exit(1);
> + goto out_fini_handler;
>
> /* CRIU needs the lxc root bind mounted so that it is the root of some
> * mount. */
> @@ -3907,15 +3900,14 @@ static bool lxcapi_restore(struct lxc_container *c, char *directory, bool verbos
>
> if (rootfs_is_blockdev(c->lxc_conf)) {
> if (do_rootfs_setup(c->lxc_conf, c->name, c->config_path) < 0)
> - exit(1);
> - }
> - else {
> + goto out_fini_handler;
> + } else {
> if (mkdir(rootfs->mount, 0755) < 0 && errno != EEXIST)
> - exit(1);
> + goto out_fini_handler;
>
> if (mount(rootfs->path, rootfs->mount, NULL, MS_BIND, NULL) < 0) {
> rmdir(rootfs->mount);
> - exit(1);
> + goto out_fini_handler;
> }
> }
>
> @@ -3930,22 +3922,28 @@ static bool lxcapi_restore(struct lxc_container *c, char *directory, bool verbos
> exec_criu(&os);
> umount(rootfs->mount);
> rmdir(rootfs->mount);
> - exit(1);
> + goto out_fini_handler;
> } else {
> int status;
> + char title[2048];
> + int ret;
>
> pid_t w = waitpid(pid, &status, 0);
> -
> if (w == -1) {
> perror("waitpid");
> goto out_fini_handler;
> }
>
> + if (sizeof(status) != write(pipe, &status, sizeof(status))) {
> + perror("write");
> + ERROR("failed to write all of status");
> + goto out_fini_handler;
> + }
> +
> if (WIFEXITED(status)) {
> if (WEXITSTATUS(status)) {
> goto out_fini_handler;
> - }
> - else {
> + } else {
> int ret;
> FILE *f = fopen(pidfile, "r");
> if (!f) {
> @@ -3969,17 +3967,70 @@ static bool lxcapi_restore(struct lxc_container *c, char *directory, bool verbos
> goto out_fini_handler;
> }
>
> - if (lxc_poll(c->name, handler)) {
> + /*
> + * See comment in lxcapi_start; we don't care if these
> + * fail because it's just a beauty thing. We just
> + * assign the return here to silence potential.
> + */
> + ret = snprintf(title, sizeof(title), "[lxc monitor] %s %s", c->config_path, c->name);
> + ret = setproctitle(title);
> +
> + ret = lxc_poll(c->name, handler);
> + if (ret)
> lxc_abort(c->name, handler);
> - goto out_fini_handler;
> - }
> + lxc_fini(c->name, handler);
> + exit(ret);
> }
>
> - has_error = false;
> -
> out_fini_handler:
> lxc_fini(c->name, handler);
> - return !has_error;
> + exit(1);
> +}
> +
> +static bool lxcapi_restore(struct lxc_container *c, char *directory, bool verbose)
> +{
> + pid_t pid;
> + int status;
> + int pipefd[2];
> +
> + if (!criu_ok(c))
> + return false;
> +
> + if (geteuid()) {
> + ERROR("Must be root to restore\n");
> + return false;
> + }
> +
> + if (pipe(pipefd)) {
d'oh, looks like I forgot to close the pipe everywhere. I'll resend
with that in a bit.
> + ERROR("failed to create pipe");
> + return false;
> + }
> +
> + pid = fork();
> + if (pid < 0)
> + return false;
> +
> + if (pid == 0) {
> + // this never returns
> + do_restore(c, pipefd[1], directory, verbose);
> + }
> +
> + if (sizeof(status) != read(pipefd[0], &status, sizeof(status))) {
> + ERROR("reading status from pipe failed");
> + goto err_wait;
> + }
> +
> + // If the criu process was killed or exited nonzero, wait() for the
> + // handler, since the restore process died. Otherwise, we don't need to
> + // wait, since the child becomes the monitor process.
> + if (!WIFEXITED(status) || WEXITSTATUS(status))
> + goto err_wait;
> + return true;
> +
> +err_wait:
> + if (wait_for_pid(pid))
> + ERROR("restore process died");
> + return false;
> }
>
> static int lxcapi_attach_run_waitl(struct lxc_container *c, lxc_attach_options_t *options, const char *program, const char *arg, ...)
> --
> 2.1.0
>
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