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samples: add a mountinfo program to demonstrate statmount()/listmount()
Add a new "mountinfo" sample userland program that demonstrates how to use statmount() and listmount() to get at the same info that /proc/pid/mountinfo provides. The output of the program tries to mimic the mountinfo procfile contents. With the -p flag, it can be pointed at an arbitrary pid to print out info about its mount namespace. With the -r flag it will attempt to walk all of the namespaces under the pid's mount namespace and dump out mount info from all of them. Signed-off-by: Jeff Layton <jlayton@kernel.org> Link: https://lore.kernel.org/r/20241115-statmount-v2-1-cd29aeff9cbb@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Jeff Layton
Christian Brauner
parent
a48bdf80ce
commit
0c8f746452
1
samples/vfs/.gitignore
vendored
1
samples/vfs/.gitignore
vendored
@ -1,3 +1,4 @@
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# SPDX-License-Identifier: GPL-2.0-only
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/test-fsmount
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/test-statx
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/mountinfo
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@ -1,4 +1,4 @@
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# SPDX-License-Identifier: GPL-2.0-only
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userprogs-always-y += test-fsmount test-statx
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userprogs-always-y += test-fsmount test-statx mountinfo
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userccflags += -I usr/include
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271
samples/vfs/mountinfo.c
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271
samples/vfs/mountinfo.c
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// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Use pidfds, nsfds, listmount() and statmount() mimic the
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* contents of /proc/self/mountinfo.
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <stdint.h>
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#include <sys/ioctl.h>
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#include <sys/syscall.h>
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#include <linux/pidfd.h>
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#include <linux/mount.h>
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#include <linux/nsfs.h>
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#include <unistd.h>
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#include <alloca.h>
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#include <getopt.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <errno.h>
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/* max mounts per listmount call */
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#define MAXMOUNTS 1024
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/* size of struct statmount (including trailing string buffer) */
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#define STATMOUNT_BUFSIZE 4096
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static bool ext_format;
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/*
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* There are no bindings in glibc for listmount() and statmount() (yet),
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* make our own here.
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*/
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static int statmount(uint64_t mnt_id, uint64_t mnt_ns_id, uint64_t mask,
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struct statmount *buf, size_t bufsize,
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unsigned int flags)
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{
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struct mnt_id_req req = {
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.size = MNT_ID_REQ_SIZE_VER0,
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.mnt_id = mnt_id,
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.param = mask,
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};
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if (mnt_ns_id) {
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req.size = MNT_ID_REQ_SIZE_VER1;
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req.mnt_ns_id = mnt_ns_id;
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}
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return syscall(__NR_statmount, &req, buf, bufsize, flags);
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}
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static ssize_t listmount(uint64_t mnt_id, uint64_t mnt_ns_id,
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uint64_t last_mnt_id, uint64_t list[], size_t num,
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unsigned int flags)
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{
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struct mnt_id_req req = {
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.size = MNT_ID_REQ_SIZE_VER0,
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.mnt_id = mnt_id,
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.param = last_mnt_id,
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};
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if (mnt_ns_id) {
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req.size = MNT_ID_REQ_SIZE_VER1;
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req.mnt_ns_id = mnt_ns_id;
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}
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return syscall(__NR_listmount, &req, list, num, flags);
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}
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static void show_mnt_attrs(uint64_t flags)
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{
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printf("%s", flags & MOUNT_ATTR_RDONLY ? "ro" : "rw");
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if (flags & MOUNT_ATTR_NOSUID)
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printf(",nosuid");
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if (flags & MOUNT_ATTR_NODEV)
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printf(",nodev");
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if (flags & MOUNT_ATTR_NOEXEC)
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printf(",noexec");
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switch (flags & MOUNT_ATTR__ATIME) {
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case MOUNT_ATTR_RELATIME:
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printf(",relatime");
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break;
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case MOUNT_ATTR_NOATIME:
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printf(",noatime");
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break;
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case MOUNT_ATTR_STRICTATIME:
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/* print nothing */
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break;
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}
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if (flags & MOUNT_ATTR_NOSYMFOLLOW)
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printf(",nosymfollow");
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if (flags & MOUNT_ATTR_IDMAP)
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printf(",idmapped");
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}
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static void show_propagation(struct statmount *sm)
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{
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if (sm->mnt_propagation & MS_SHARED)
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printf(" shared:%llu", sm->mnt_peer_group);
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if (sm->mnt_propagation & MS_SLAVE) {
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printf(" master:%llu", sm->mnt_master);
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if (sm->mnt_master)
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printf(" propagate_from:%llu", sm->propagate_from);
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}
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if (sm->mnt_propagation & MS_UNBINDABLE)
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printf(" unbindable");
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}
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static void show_sb_flags(uint64_t flags)
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{
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printf("%s", flags & MS_RDONLY ? "ro" : "rw");
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if (flags & MS_SYNCHRONOUS)
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printf(",sync");
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if (flags & MS_DIRSYNC)
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printf(",dirsync");
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if (flags & MS_MANDLOCK)
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printf(",mand");
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if (flags & MS_LAZYTIME)
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printf(",lazytime");
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}
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static int dump_mountinfo(uint64_t mnt_id, uint64_t mnt_ns_id)
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{
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int ret;
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struct statmount *buf = alloca(STATMOUNT_BUFSIZE);
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const uint64_t mask = STATMOUNT_SB_BASIC | STATMOUNT_MNT_BASIC |
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STATMOUNT_PROPAGATE_FROM | STATMOUNT_FS_TYPE |
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STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT |
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STATMOUNT_MNT_OPTS | STATMOUNT_FS_SUBTYPE |
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STATMOUNT_SB_SOURCE;
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ret = statmount(mnt_id, mnt_ns_id, mask, buf, STATMOUNT_BUFSIZE, 0);
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if (ret < 0) {
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perror("statmount");
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return 1;
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}
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if (ext_format)
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printf("0x%lx 0x%lx 0x%llx ", mnt_ns_id, mnt_id, buf->mnt_parent_id);
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printf("%u %u %u:%u %s %s ", buf->mnt_id_old, buf->mnt_parent_id_old,
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buf->sb_dev_major, buf->sb_dev_minor,
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&buf->str[buf->mnt_root],
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&buf->str[buf->mnt_point]);
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show_mnt_attrs(buf->mnt_attr);
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show_propagation(buf);
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printf(" - %s", &buf->str[buf->fs_type]);
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if (buf->mask & STATMOUNT_FS_SUBTYPE)
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printf(".%s", &buf->str[buf->fs_subtype]);
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if (buf->mask & STATMOUNT_SB_SOURCE)
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printf(" %s ", &buf->str[buf->sb_source]);
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else
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printf(" :none ");
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show_sb_flags(buf->sb_flags);
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if (buf->mask & STATMOUNT_MNT_OPTS)
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printf(",%s", &buf->str[buf->mnt_opts]);
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printf("\n");
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return 0;
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}
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static int dump_mounts(uint64_t mnt_ns_id)
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{
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uint64_t mntid[MAXMOUNTS];
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uint64_t last_mnt_id = 0;
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ssize_t count;
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int i;
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/*
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* Get a list of all mntids in mnt_ns_id. If it returns MAXMOUNTS
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* mounts, then go again until we get everything.
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*/
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do {
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count = listmount(LSMT_ROOT, mnt_ns_id, last_mnt_id, mntid, MAXMOUNTS, 0);
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if (count < 0 || count > MAXMOUNTS) {
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errno = count < 0 ? errno : count;
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perror("listmount");
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return 1;
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}
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/* Walk the returned mntids and print info about each */
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for (i = 0; i < count; ++i) {
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int ret = dump_mountinfo(mntid[i], mnt_ns_id);
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if (ret != 0)
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return ret;
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}
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/* Set up last_mnt_id to pick up where we left off */
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last_mnt_id = mntid[count - 1];
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} while (count == MAXMOUNTS);
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return 0;
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}
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static void usage(const char * const prog)
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{
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printf("Usage:\n");
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printf("%s [-e] [-p pid] [-r] [-h]\n", prog);
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printf(" -e: extended format\n");
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printf(" -h: print usage message\n");
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printf(" -p: get mount namespace from given pid\n");
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printf(" -r: recursively print all mounts in all child namespaces\n");
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}
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int main(int argc, char * const *argv)
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{
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struct mnt_ns_info mni = { .size = MNT_NS_INFO_SIZE_VER0 };
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int pidfd, mntns, ret, opt;
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pid_t pid = getpid();
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bool recursive = false;
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while ((opt = getopt(argc, argv, "ehp:r")) != -1) {
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switch (opt) {
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case 'e':
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ext_format = true;
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break;
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case 'h':
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usage(argv[0]);
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return 0;
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case 'p':
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pid = atoi(optarg);
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break;
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case 'r':
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recursive = true;
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break;
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}
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}
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/* Get a pidfd for pid */
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pidfd = syscall(SYS_pidfd_open, pid, 0);
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if (pidfd < 0) {
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perror("pidfd_open");
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return 1;
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}
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/* Get the mnt namespace for pidfd */
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mntns = ioctl(pidfd, PIDFD_GET_MNT_NAMESPACE, NULL);
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if (mntns < 0) {
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perror("PIDFD_GET_MNT_NAMESPACE");
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return 1;
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}
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close(pidfd);
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/* get info about mntns. In particular, the mnt_ns_id */
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ret = ioctl(mntns, NS_MNT_GET_INFO, &mni);
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if (ret < 0) {
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perror("NS_MNT_GET_INFO");
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return 1;
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}
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do {
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int ret;
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ret = dump_mounts(mni.mnt_ns_id);
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if (ret)
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return ret;
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if (!recursive)
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break;
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/* get the next mntns (and overwrite the old mount ns info) */
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ret = ioctl(mntns, NS_MNT_GET_NEXT, &mni);
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close(mntns);
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mntns = ret;
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} while (mntns >= 0);
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return 0;
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}
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