On Tue, Nov 12, 2024 at 04:21:23PM -0500, Jeff Layton wrote:
> 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@xxxxxxxxxx>
> ---
> We had some recent queries internally asking how to use the new
> statmount() and listmount() interfaces. I was doing some other work in
> this area, so I whipped up this tool. My hope is that this will
> represent something of a "rosetta stone" for how to translate between
> mountinfo and statmount(), and an example for other people looking to
> use the new interfaces.
>
> It may also be possible to use this as the basis for a statmount()
> testcase. We can call this program, and compare its output to the
> mountinfo file.
> ---
Yes, that's great. Thanks for doing that!
> samples/vfs/.gitignore | 1 +
> samples/vfs/Makefile | 2 +-
> samples/vfs/mountinfo.c | 271 ++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 273 insertions(+), 1 deletion(-)
>
> diff --git a/samples/vfs/.gitignore b/samples/vfs/.gitignore
> index 79212d91285bca72b0ff85f28aaccd2e803ac092..33a03cffe072fe2466c9df30ad47e9c58b0eea7c 100644
> --- a/samples/vfs/.gitignore
> +++ b/samples/vfs/.gitignore
> @@ -1,3 +1,4 @@
> # SPDX-License-Identifier: GPL-2.0-only
> /test-fsmount
> /test-statx
> +/mountinfo
> diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
> index 6377a678134acf0d682151d751d2f5042dbf5e0a..fb9bb33fdc751556e806aa897f0dbd48f7e3a4d8 100644
> --- a/samples/vfs/Makefile
> +++ b/samples/vfs/Makefile
> @@ -1,4 +1,4 @@
> # SPDX-License-Identifier: GPL-2.0-only
> -userprogs-always-y += test-fsmount test-statx
> +userprogs-always-y += test-fsmount test-statx mountinfo
>
> userccflags += -I usr/include
> diff --git a/samples/vfs/mountinfo.c b/samples/vfs/mountinfo.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..7f430835dd7fb1a3d87d98cad00c619dbb5c6f70
> --- /dev/null
> +++ b/samples/vfs/mountinfo.c
> @@ -0,0 +1,271 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +/*
> + * Use pidfds, nsfds, listmount() and statmount() mimic the
> + * contents of /proc/self/mountinfo.
> + */
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <sys/ioctl.h>
> +#include <sys/syscall.h>
> +#include <linux/pidfd.h>
> +#include <linux/mount.h>
> +#include <linux/nsfs.h>
> +#include <unistd.h>
> +#include <alloca.h>
> +#include <getopt.h>
> +#include <stdlib.h>
> +#include <stdbool.h>
> +#include <errno.h>
> +
> +/* max mounts per listmount call */
> +#define MAXMOUNTS 1024
> +
> +/* size of struct statmount (including trailing string buffer) */
> +#define STATMOUNT_BUFSIZE 4096
> +
> +static bool ext_format;
> +
> +/*
> + * There are no bindings in glibc for listmount() and statmount() (yet),
> + * make our own here.
> + */
> +static int statmount(uint64_t mnt_id, uint64_t mnt_ns_id, uint64_t mask,
> + struct statmount *buf, size_t bufsize,
> + unsigned int flags)
> +{
> + struct mnt_id_req req = {
> + .size = MNT_ID_REQ_SIZE_VER0,
> + .mnt_id = mnt_id,
> + .param = mask,
> + };
> +
> + if (mnt_ns_id) {
> + req.size = MNT_ID_REQ_SIZE_VER1;
> + req.mnt_ns_id = mnt_ns_id;
> + }
> +
> + return syscall(__NR_statmount, &req, buf, bufsize, flags);
> +}
> +
> +static ssize_t listmount(uint64_t mnt_id, uint64_t mnt_ns_id,
> + uint64_t last_mnt_id, uint64_t list[], size_t num,
> + unsigned int flags)
> +{
> + struct mnt_id_req req = {
> + .size = MNT_ID_REQ_SIZE_VER0,
> + .mnt_id = mnt_id,
> + .param = last_mnt_id,
> + };
> +
> + if (mnt_ns_id) {
> + req.size = MNT_ID_REQ_SIZE_VER1;
> + req.mnt_ns_id = mnt_ns_id;
> + }
> +
> + return syscall(__NR_listmount, &req, list, num, flags);
> +}
> +
> +static void show_mnt_attrs(uint64_t flags)
> +{
> + printf("%s", flags & MOUNT_ATTR_RDONLY ? "ro" : "rw");
> +
> + if (flags & MOUNT_ATTR_NOSUID)
> + printf(",nosuid");
> + if (flags & MOUNT_ATTR_NODEV)
> + printf(",nodev");
> + if (flags & MOUNT_ATTR_NOEXEC)
> + printf(",noexec");
> +
> + switch (flags & MOUNT_ATTR__ATIME) {
> + case MOUNT_ATTR_RELATIME:
> + printf(",relatime");
> + break;
> + case MOUNT_ATTR_NOATIME:
> + printf(",noatime");
> + break;
> + case MOUNT_ATTR_STRICTATIME:
> + /* print nothing */
> + break;
> + }
> +
> + if (flags & MOUNT_ATTR_NOSYMFOLLOW)
> + printf(",nosymfollow");
> + if (flags & MOUNT_ATTR_IDMAP)
> + printf(",idmapped");
> +}
> +
> +static void show_propagation(struct statmount *sm)
> +{
> + if (sm->mnt_propagation & MS_SHARED)
> + printf(" shared:%llu", sm->mnt_peer_group);
> + if (sm->mnt_propagation & MS_SLAVE) {
> + printf(" master:%llu", sm->mnt_master);
> + if (sm->mnt_master)
> + printf(" propagate_from:%llu", sm->propagate_from);
> + }
> + if (sm->mnt_propagation & MS_UNBINDABLE)
> + printf(" unbindable");
> +}
> +
> +static void show_sb_flags(uint64_t flags)
> +{
> + printf("%s", flags & MS_RDONLY ? "ro" : "rw");
> + if (flags & MS_SYNCHRONOUS)
> + printf(",sync");
> + if (flags & MS_DIRSYNC)
> + printf(",dirsync");
> + if (flags & MS_MANDLOCK)
> + printf(",mand");
> + if (flags & MS_LAZYTIME)
> + printf(",lazytime");
> +}
> +
> +static int dump_mountinfo(uint64_t mnt_id, uint64_t mnt_ns_id)
> +{
> + int ret;
> + struct statmount *buf = alloca(STATMOUNT_BUFSIZE);
> + const uint64_t mask = STATMOUNT_SB_BASIC | STATMOUNT_MNT_BASIC |
> + STATMOUNT_PROPAGATE_FROM | STATMOUNT_FS_TYPE |
> + STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT |
> + STATMOUNT_MNT_OPTS | STATMOUNT_FS_SUBTYPE |
> + STATMOUNT_SB_SOURCE;
> +
> + ret = statmount(mnt_id, mnt_ns_id, mask, buf, STATMOUNT_BUFSIZE, 0);
> + if (ret < 0) {
> + perror("statmount");
> + return 1;
> + }
> +
> + if (ext_format)
> + printf("0x%lx 0x%lx 0x%llx ", mnt_ns_id, mnt_id, buf->mnt_parent_id);
> +
> + printf("%u %u %u:%u %s %s ", buf->mnt_id_old, buf->mnt_parent_id_old,
> + buf->sb_dev_major, buf->sb_dev_minor,
> + &buf->str[buf->mnt_root],
> + &buf->str[buf->mnt_point]);
> + show_mnt_attrs(buf->mnt_attr);
> + show_propagation(buf);
> +
> + printf(" - %s", &buf->str[buf->fs_type]);
> + if (buf->mask & STATMOUNT_FS_SUBTYPE)
> + printf(".%s", &buf->str[buf->fs_subtype]);
> + if (buf->mask & STATMOUNT_SB_SOURCE)
> + printf(" %s ", &buf->str[buf->sb_source]);
> + else
> + printf(" :none ");
> +
> + show_sb_flags(buf->sb_flags);
> + if (buf->mask & STATMOUNT_MNT_OPTS)
> + printf(",%s", &buf->str[buf->mnt_opts]);
> + printf("\n");
> + return 0;
> +}
> +
> +static int dump_mounts(uint64_t mnt_ns_id)
> +{
> + uint64_t mntid[MAXMOUNTS];
> + uint64_t last_mnt_id = 0;
> + ssize_t count;
> + int i;
> +
> + /*
> + * Get a list of all mntids in mnt_ns_id. If it returns MAXMOUNTS
> + * mounts, then go again until we get everything.
> + */
> + do {
> + count = listmount(LSMT_ROOT, mnt_ns_id, last_mnt_id, mntid, MAXMOUNTS, 0);
> + if (count < 0 || count > MAXMOUNTS) {
> + errno = count < 0 ? errno : count;
> + perror("listmount");
> + return 1;
> + }
> +
> + /* Walk the returned mntids and print info about each */
> + for (i = 0; i < count; ++i) {
> + int ret = dump_mountinfo(mntid[i], mnt_ns_id);
> +
> + if (ret != 0)
> + return ret;
> + }
> + /* Set up last_mnt_id to pick up where we left off */
> + last_mnt_id = mntid[count - 1] + 1;
> + } while (count == MAXMOUNTS);
> + return 0;
> +}
> +
> +static void usage(const char * const prog)
> +{
> + printf("Usage:\n");
> + printf("%s [-e] [-p pid] [-r] [-h]\n", prog);
> + printf(" -e: extended format\n");
> + printf(" -h: print usage message\n");
> + printf(" -p: get mount namespace from given pid\n");
> + printf(" -r: recursively print all mounts in all child namespaces\n");
> +}
> +
> +int main(int argc, char * const *argv)
> +{
> + struct mnt_ns_info mni = { .size = MNT_NS_INFO_SIZE_VER0 };
> + int pidfd, mntns, ret, opt;
> + pid_t pid = getpid();
> + bool recursive = false;
> +
> + while ((opt = getopt(argc, argv, "ehp:r")) != -1) {
> + switch (opt) {
> + case 'e':
> + ext_format = true;
> + break;
> + case 'h':
> + usage(argv[0]);
> + return 0;
> + case 'p':
> + pid = atoi(optarg);
> + break;
> + case 'r':
> + recursive = true;
> + break;
> + }
> + }
> +
> + /* Get a pidfd for pid */
> + pidfd = syscall(SYS_pidfd_open, pid, 0);
> + if (pidfd < 0) {
> + perror("pidfd_open");
> + return 1;
> + }
> +
> + /* Get the mnt namespace for pidfd */
> + mntns = ioctl(pidfd, PIDFD_GET_MNT_NAMESPACE, NULL);
> + if (mntns < 0) {
> + perror("PIDFD_GET_MNT_NAMESPACE");
> + return 1;
> + }
> + close(pidfd);
> +
> + /* get info about mntns. In particular, the mnt_ns_id */
> + ret = ioctl(mntns, NS_MNT_GET_INFO, &mni);
> + if (ret < 0) {
> + perror("NS_MNT_GET_INFO");
> + return 1;
> + }
> +
> + do {
> + int ret;
> +
> + ret = dump_mounts(mni.mnt_ns_id);
> + if (ret)
> + return ret;
> +
> + if (!recursive)
> + break;
> +
> + /* get the next mntns (and overwrite the old mount ns info) */
> + ret = ioctl(mntns, NS_MNT_GET_NEXT, &mni);
> + close(mntns);
> + mntns = ret;
> + } while (mntns >= 0);
> +
> + return 0;
> +}
>
> ---
> base-commit: 3def14eb3d2e9d452623af64e315605150292aa8
> change-id: 20241112-statmount-77808bc02302
>
> Best regards,
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
