[lxc-devel] [PATCH v3 7/7] added the unmount-namespace hook
Wolfgang Bumiller
w.bumiller at proxmox.com
Tue Oct 6 08:01:07 UTC 2015
Signed-off-by: Wolfgang Bumiller <w.bumiller at proxmox.com>
---
hooks/Makefile.am | 6 ++
hooks/unmount-namespace.c | 213 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 219 insertions(+)
create mode 100644 hooks/unmount-namespace.c
diff --git a/hooks/Makefile.am b/hooks/Makefile.am
index be55601..ef82083 100644
--- a/hooks/Makefile.am
+++ b/hooks/Makefile.am
@@ -6,4 +6,10 @@ hooks_SCRIPTS = \
ubuntu-cloud-prep \
squid-deb-proxy-client
+hooks_PROGRAMS = \
+ unmount-namespace
+
+unmount_namespace_SOURCES = \
+ unmount-namespace.c
+
EXTRA_DIST=$(hooks_SCRIPTS)
diff --git a/hooks/unmount-namespace.c b/hooks/unmount-namespace.c
new file mode 100644
index 0000000..488c9cc
--- /dev/null
+++ b/hooks/unmount-namespace.c
@@ -0,0 +1,213 @@
+/*
+ * Copyright © 2015 Wolfgang Bumiller <w.bumiller at proxmox.com>.
+ * Copyright © 2015 Proxmox Server Solutions GmbH
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * --
+ *
+ * This stop-hook unmounts everything in the container's namespace, and thereby
+ * waits for all calls commands to finish. This is useful when one needs to be
+ * sure that network filesystems are finished unmounting in the namespace
+ * before continuing with other tasks. Without this hook the cleanup of mounts
+ * is done by the kernel in the background after all the references to the
+ * namespaces are gone.
+ */
+
+#define _GNU_SOURCE /* setns */
+#include <stdio.h> /* fdopen, getmntent, endmntent */
+#include <stdlib.h> /* malloc, qsort */
+#include <unistd.h> /* close */
+#include <string.h> /* strcmp, strncmp, strdup, strerror */
+#include <sched.h> /* setns */
+#include <sys/mount.h> /* umount2 */
+#include <sys/types.h> /* openat, open */
+#include <sys/stat.h> /* openat, open */
+#include <fcntl.h> /* openat, open */
+#include <mntent.h> /* getmntent, endmntent */
+#include <errno.h> /* errno */
+
+struct mount {
+ char *src; /* currently not used */
+ char *dst;
+ char *fs; /* currently not used */
+};
+
+static void mount_free(struct mount *mnt) {
+ free(mnt->src);
+ free(mnt->dst);
+ free(mnt->fs);
+}
+
+static int mount_cmp_dst(const void *a_, const void *b_) {
+ struct mount *a = (struct mount*)a_;
+ struct mount *b = (struct mount*)b_;
+ return strcmp(b->dst, a->dst); /* swapped order */
+}
+
+/* Unmounting /dev/pts fails, and so /dev also fails, but /dev is not what
+ * we're interested in. (There might also still be /dev/cgroup mounts).
+ */
+static int mount_should_error(const struct mount *mnt) {
+ const char *dst = mnt->dst;
+ return !(strncmp(dst, "/dev", 4) == 0 && (dst[4] == 0 || dst[4] == '/'));
+}
+
+/* Read mounts from 'self/mounts' relative to a directory filedescriptor.
+ * Before entering the container we open a handle to /proc on the host as we
+ * need to access /proc/self/mounts and the container's /proc doesn't contain
+ * our /self. We then use openat(2) to avoid having to mount a temporary /proc.
+ */
+static int read_mounts(int procfd, struct mount **mp, size_t *countp) {
+ int fd;
+ struct mntent *ent;
+ FILE *mf;
+ size_t capacity = 32;
+ size_t count = 0;
+ struct mount *mounts = (struct mount*)malloc(capacity * sizeof(*mounts));
+
+ if (!mounts) {
+ errno = ENOMEM;
+ return 0;
+ }
+
+ *mp = NULL;
+ *countp = 0;
+
+ fd = openat(procfd, "self/mounts", O_RDONLY);
+ if (fd < 0)
+ return 0;
+
+ mf = fdopen(fd, "r");
+ if (!mf) {
+ int error = errno;
+ close(fd);
+ errno = error;
+ return 0;
+ }
+ while ((ent = getmntent(mf))) {
+ struct mount *new;
+ if (count == capacity) {
+ capacity *= 2;
+ new = (struct mount*)realloc(mounts, capacity * sizeof(*mounts));
+ if (!new)
+ goto out_alloc_entry;
+ mounts = new;
+ }
+ new = &mounts[count++];
+ new->src = strdup(ent->mnt_fsname);
+ new->dst = strdup(ent->mnt_dir);
+ new->fs = strdup(ent->mnt_type);
+ if (!new->src || !new->dst || !new->fs)
+ goto out_alloc_entry;
+ }
+ endmntent(mf);
+
+ *mp = mounts;
+ *countp = count;
+
+ return 1;
+
+out_alloc_entry:
+ endmntent(mf);
+ while (count--) {
+ free(mounts[count].src);
+ free(mounts[count].dst);
+ free(mounts[count].fs);
+ }
+ free(mounts);
+ errno = ENOMEM;
+ return 0;
+}
+
+int main(int argc, char **argv) {
+ int i, procfd, ctmntfd;
+ struct mount *mounts;
+ size_t zi, count = 0;
+ const char *mntns = NULL;
+
+ if (argc < 4 || strcmp(argv[2], "lxc") != 0) {
+ fprintf(stderr, "%s: usage error, expected LXC hook arguments\n", argv[0]);
+ return 2;
+ }
+
+ if (strcmp(argv[3], "stop") != 0)
+ return 0;
+
+ for (i = 4; i != argc; ++i) {
+ if (!strncmp(argv[i], "mnt:", 4)) {
+ mntns = argv[i] + 4;
+ break;
+ }
+ }
+
+ if (!mntns) {
+ fprintf(stderr, "%s: no mount namespace provided\n", argv[0]);
+ return 3;
+ }
+
+ /* Open a handle to /proc on the host as we need to access /proc/self/mounts
+ * and the container's /proc doesn't contain our /self. See read_mounts().
+ */
+ procfd = open("/proc", O_RDONLY | O_DIRECTORY | O_PATH);
+ if (procfd < 0) {
+ fprintf(stderr, "%s: failed to open /proc: %s\n", argv[0], strerror(errno));
+ return 4;
+ }
+
+ /* Open the mount namespace and enter it. */
+ ctmntfd = open(mntns, O_RDONLY);
+ if (ctmntfd < 0) {
+ fprintf(stderr, "%s: failed to open mount namespace: %s\n",
+ argv[0], strerror(errno));
+ close(procfd);
+ return 5;
+ }
+
+ if (setns(ctmntfd, CLONE_NEWNS) != 0) {
+ fprintf(stderr, "%s: failed to attach to namespace: %s\n",
+ argv[0], strerror(errno));
+ close(ctmntfd);
+ close(procfd);
+ return 6;
+ }
+ close(ctmntfd);
+
+ /* Now read [[procfd]]/self/mounts */
+ if (!read_mounts(procfd, &mounts, &count)) {
+ fprintf(stderr, "%s: failed to read mountpoints: %s\n",
+ argv[0], strerror(errno));
+ close(procfd);
+ return 7;
+ }
+ close(procfd);
+
+ /* Just sort to get a sane unmount-order... */
+ qsort(mounts, count, sizeof(*mounts), &mount_cmp_dst);
+
+ for (zi = 0; zi != count; ++zi) {
+ /* fprintf(stderr, "Unmount: %s\n", mounts[zi].dst); */
+ if (umount2(mounts[zi].dst, 0) != 0) {
+ int error = errno;
+ if (mount_should_error(&mounts[zi])) {
+ fprintf(stderr, "%s: failed to unmount %s: %s\n",
+ argv[0], mounts[zi].dst, strerror(error));
+ }
+ }
+ mount_free(&mounts[zi]);
+ }
+ free(mounts);
+
+ return 0;
+}
--
2.1.4
More information about the lxc-devel
mailing list