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samples: add test-list-all-mounts
Add a sample program illustrating how to list all mounts in all mount namespaces. Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-10-6e3cdaf9b280@kernel.org Reviewed-by: Jeff Layton <[email protected]> Signed-off-by: Christian Brauner <[email protected]>
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‎samples/vfs/.gitignore

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# SPDX-License-Identifier: GPL-2.0-only
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/test-fsmount
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/test-list-all-mounts
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/test-statx
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/mountinfo

‎samples/vfs/Makefile

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# SPDX-License-Identifier: GPL-2.0-only
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userprogs-always-y += test-fsmount test-statx mountinfo
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userprogs-always-y += test-fsmount test-statx mountinfo test-list-all-mounts
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userccflags += -I usr/include

‎samples/vfs/test-list-all-mounts.c

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// SPDX-License-Identifier: GPL-2.0-or-later
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// Copyright (c) 2024 Christian Brauner <[email protected]>
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#define _GNU_SOURCE
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#include <errno.h>
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#include <limits.h>
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#include <linux/types.h>
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#include <stdio.h>
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#include <sys/ioctl.h>
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#include <sys/syscall.h>
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#include "../../tools/testing/selftests/pidfd/pidfd.h"
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#define die_errno(format, ...) \
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do { \
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fprintf(stderr, "%m | %s: %d: %s: " format "\n", __FILE__, \
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__LINE__, __func__, ##__VA_ARGS__); \
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exit(EXIT_FAILURE); \
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} while (0)
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/* Get the id for a mount namespace */
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#define NS_GET_MNTNS_ID _IO(0xb7, 0x5)
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/* Get next mount namespace. */
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struct mnt_ns_info {
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__u32 size;
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__u32 nr_mounts;
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__u64 mnt_ns_id;
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};
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#define MNT_NS_INFO_SIZE_VER0 16 /* size of first published struct */
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/* Get information about namespace. */
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#define NS_MNT_GET_INFO _IOR(0xb7, 10, struct mnt_ns_info)
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/* Get next namespace. */
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#define NS_MNT_GET_NEXT _IOR(0xb7, 11, struct mnt_ns_info)
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/* Get previous namespace. */
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#define NS_MNT_GET_PREV _IOR(0xb7, 12, struct mnt_ns_info)
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#define PIDFD_GET_MNT_NAMESPACE _IO(0xFF, 3)
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#ifndef __NR_listmount
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#define __NR_listmount 458
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#endif
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#ifndef __NR_statmount
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#define __NR_statmount 457
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#endif
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/* @mask bits for statmount(2) */
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#define STATMOUNT_SB_BASIC 0x00000001U /* Want/got sb_... */
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#define STATMOUNT_MNT_BASIC 0x00000002U /* Want/got mnt_... */
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#define STATMOUNT_PROPAGATE_FROM 0x00000004U /* Want/got propagate_from */
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#define STATMOUNT_MNT_ROOT 0x00000008U /* Want/got mnt_root */
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#define STATMOUNT_MNT_POINT 0x00000010U /* Want/got mnt_point */
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#define STATMOUNT_FS_TYPE 0x00000020U /* Want/got fs_type */
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#define STATMOUNT_MNT_NS_ID 0x00000040U /* Want/got mnt_ns_id */
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#define STATMOUNT_MNT_OPTS 0x00000080U /* Want/got mnt_opts */
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#define STATX_MNT_ID_UNIQUE 0x00004000U /* Want/got extended stx_mount_id */
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struct statmount {
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__u32 size;
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__u32 mnt_opts;
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__u64 mask;
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__u32 sb_dev_major;
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__u32 sb_dev_minor;
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__u64 sb_magic;
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__u32 sb_flags;
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__u32 fs_type;
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__u64 mnt_id;
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__u64 mnt_parent_id;
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__u32 mnt_id_old;
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__u32 mnt_parent_id_old;
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__u64 mnt_attr;
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__u64 mnt_propagation;
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__u64 mnt_peer_group;
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__u64 mnt_master;
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__u64 propagate_from;
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__u32 mnt_root;
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__u32 mnt_point;
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__u64 mnt_ns_id;
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__u64 __spare2[49];
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char str[];
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};
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struct mnt_id_req {
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__u32 size;
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__u32 spare;
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__u64 mnt_id;
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__u64 param;
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__u64 mnt_ns_id;
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};
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#define MNT_ID_REQ_SIZE_VER1 32 /* sizeof second published struct */
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#define LSMT_ROOT 0xffffffffffffffff /* root mount */
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static int __statmount(__u64 mnt_id, __u64 mnt_ns_id, __u64 mask,
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struct statmount *stmnt, 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_VER1,
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.mnt_id = mnt_id,
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.param = mask,
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.mnt_ns_id = mnt_ns_id,
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};
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return syscall(__NR_statmount, &req, stmnt, bufsize, flags);
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}
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static struct statmount *sys_statmount(__u64 mnt_id, __u64 mnt_ns_id,
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__u64 mask, unsigned int flags)
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{
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size_t bufsize = 1 << 15;
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struct statmount *stmnt = NULL, *tmp = NULL;
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int ret;
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for (;;) {
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tmp = realloc(stmnt, bufsize);
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if (!tmp)
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goto out;
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stmnt = tmp;
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ret = __statmount(mnt_id, mnt_ns_id, mask, stmnt, bufsize, flags);
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if (!ret)
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return stmnt;
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if (errno != EOVERFLOW)
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goto out;
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bufsize <<= 1;
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if (bufsize >= UINT_MAX / 2)
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goto out;
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}
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out:
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free(stmnt);
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return NULL;
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}
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static ssize_t sys_listmount(__u64 mnt_id, __u64 last_mnt_id, __u64 mnt_ns_id,
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__u64 list[], size_t num, 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_VER1,
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.mnt_id = mnt_id,
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.param = last_mnt_id,
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.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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int main(int argc, char *argv[])
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{
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#define LISTMNT_BUFFER 10
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__u64 list[LISTMNT_BUFFER], last_mnt_id = 0;
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int ret, pidfd, fd_mntns;
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struct mnt_ns_info info = {};
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pidfd = sys_pidfd_open(getpid(), 0);
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if (pidfd < 0)
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die_errno("pidfd_open failed");
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fd_mntns = ioctl(pidfd, PIDFD_GET_MNT_NAMESPACE, 0);
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if (fd_mntns < 0)
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die_errno("ioctl(PIDFD_GET_MNT_NAMESPACE) failed");
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ret = ioctl(fd_mntns, NS_MNT_GET_INFO, &info);
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if (ret < 0)
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die_errno("ioctl(NS_GET_MNTNS_ID) failed");
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printf("Listing %u mounts for mount namespace %llu\n",
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info.nr_mounts, info.mnt_ns_id);
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for (;;) {
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ssize_t nr_mounts;
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next:
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nr_mounts = sys_listmount(LSMT_ROOT, last_mnt_id,
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info.mnt_ns_id, list, LISTMNT_BUFFER,
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0);
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if (nr_mounts <= 0) {
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int fd_mntns_next;
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printf("Finished listing %u mounts for mount namespace %llu\n\n",
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info.nr_mounts, info.mnt_ns_id);
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fd_mntns_next = ioctl(fd_mntns, NS_MNT_GET_NEXT, &info);
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if (fd_mntns_next < 0) {
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if (errno == ENOENT) {
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printf("Finished listing all mount namespaces\n");
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exit(0);
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}
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die_errno("ioctl(NS_MNT_GET_NEXT) failed");
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}
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close(fd_mntns);
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fd_mntns = fd_mntns_next;
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last_mnt_id = 0;
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printf("Listing %u mounts for mount namespace %llu\n",
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info.nr_mounts, info.mnt_ns_id);
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goto next;
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}
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for (size_t cur = 0; cur < nr_mounts; cur++) {
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struct statmount *stmnt;
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last_mnt_id = list[cur];
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stmnt = sys_statmount(last_mnt_id, info.mnt_ns_id,
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STATMOUNT_SB_BASIC |
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STATMOUNT_MNT_BASIC |
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STATMOUNT_MNT_ROOT |
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STATMOUNT_MNT_POINT |
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STATMOUNT_MNT_NS_ID |
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STATMOUNT_MNT_OPTS |
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STATMOUNT_FS_TYPE, 0);
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if (!stmnt) {
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printf("Failed to statmount(%llu) in mount namespace(%llu)\n",
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last_mnt_id, info.mnt_ns_id);
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continue;
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}
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printf("mnt_id:\t\t%llu\nmnt_parent_id:\t%llu\nfs_type:\t%s\nmnt_root:\t%s\nmnt_point:\t%s\nmnt_opts:\t%s\n\n",
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stmnt->mnt_id,
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stmnt->mnt_parent_id,
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stmnt->str + stmnt->fs_type,
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stmnt->str + stmnt->mnt_root,
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stmnt->str + stmnt->mnt_point,
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stmnt->str + stmnt->mnt_opts);
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free(stmnt);
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}
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}
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exit(0);
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}

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