// SPDX-License-Identifier: GPL-2.0-or-later

/*
 * Use pidfds, nsfds, listmount() and statmount() mimic the
 * contents of /proc/self/mountinfo.
 */
#define _GNU_SOURCE
#define __SANE_USERSPACE_TYPES__
#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <alloca.h>
#include <getopt.h>
#include <stdlib.h>
#include <stdbool.h>
#include <errno.h>

#include "samples-vfs.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;

#ifndef __NR_pidfd_open
#define __NR_pidfd_open -1
#endif

/*
 * There are no bindings in glibc for listmount() and statmount() (yet),
 * make our own here.
 */
static int statmount(__u64 mnt_id, __u64 mnt_ns_id, __u64 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(__u64 mnt_id, __u64 mnt_ns_id, __u64 last_mnt_id,
                         __u64 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(__u64 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_NODIRATIME)
                printf(",nodiratime");
        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->propagate_from && sm->propagate_from != sm->mnt_master)
                        printf(" propagate_from:%llu", sm->propagate_from);
        }
        if (sm->mnt_propagation & MS_UNBINDABLE)
                printf(" unbindable");
}

static void show_sb_flags(__u64 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(__u64 mnt_id, __u64 mnt_ns_id)
{
        int ret;
        struct statmount *buf = alloca(STATMOUNT_BUFSIZE);
        const __u64 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%llx 0x%llx 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(__u64 mnt_ns_id)
{
        __u64 mntid[MAXMOUNTS];
        __u64 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];
        } 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(__NR_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;
}