On Tue, 2024-12-10 at 21:58 +0100, Christian Brauner wrote:
> Add a sample program illustrating how to list all mounts in all mount
> namespaces.
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
> ---
> samples/vfs/.gitignore | 1 +
> samples/vfs/Makefile | 2 +-
> samples/vfs/test-list-all-mounts.c | 235 +++++++++++++++++++++++++++++++++++++
> 3 files changed, 237 insertions(+), 1 deletion(-)
>
> diff --git a/samples/vfs/.gitignore b/samples/vfs/.gitignore
> index 79212d91285bca72b0ff85f28aaccd2e803ac092..8694dd17b318768b975ece5c7cd450c2cca67318 100644
> --- a/samples/vfs/.gitignore
> +++ b/samples/vfs/.gitignore
> @@ -1,3 +1,4 @@
> # SPDX-License-Identifier: GPL-2.0-only
> /test-fsmount
> +/test-list-all-mounts
> /test-statx
> diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
> index 6377a678134acf0d682151d751d2f5042dbf5e0a..301be72a52a0e376c7ebe235cc2058992919cc78 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 test-list-all-mounts
>
>
There will be a minor merge conflict above vs. the new mountinfo
program sitting in your tree.
>
> userccflags += -I usr/include
> diff --git a/samples/vfs/test-list-all-mounts.c b/samples/vfs/test-list-all-mounts.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..f372d5aea4717fd1ab3d4b3f9af79316cd5dd3d3
> --- /dev/null
> +++ b/samples/vfs/test-list-all-mounts.c
> @@ -0,0 +1,235 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +// Copyright (c) 2024 Christian Brauner <brauner@xxxxxxxxxx>
> +
> +#define _GNU_SOURCE
> +#include <errno.h>
> +#include <limits.h>
> +#include <linux/types.h>
> +#include <stdio.h>
> +#include <sys/ioctl.h>
> +#include <sys/syscall.h>
> +
> +#include "../../tools/testing/selftests/pidfd/pidfd.h"
> +
> +#define die_errno(format, ...) \
> + do { \
> + fprintf(stderr, "%m | %s: %d: %s: " format "\n", __FILE__, \
> + __LINE__, __func__, ##__VA_ARGS__); \
> + exit(EXIT_FAILURE); \
> + } while (0)
> +
> +/* Get the id for a mount namespace */
> +#define NS_GET_MNTNS_ID _IO(0xb7, 0x5)
> +/* Get next mount namespace. */
> +
> +struct mnt_ns_info {
> + __u32 size;
> + __u32 nr_mounts;
> + __u64 mnt_ns_id;
> +};
> +
> +#define MNT_NS_INFO_SIZE_VER0 16 /* size of first published struct */
> +
> +/* Get information about namespace. */
> +#define NS_MNT_GET_INFO _IOR(0xb7, 10, struct mnt_ns_info)
> +/* Get next namespace. */
> +#define NS_MNT_GET_NEXT _IOR(0xb7, 11, struct mnt_ns_info)
> +/* Get previous namespace. */
> +#define NS_MNT_GET_PREV _IOR(0xb7, 12, struct mnt_ns_info)
> +
> +#define PIDFD_GET_MNT_NAMESPACE _IO(0xFF, 3)
> +
> +#ifndef __NR_listmount
> +#define __NR_listmount 458
> +#endif
> +
> +#ifndef __NR_statmount
> +#define __NR_statmount 457
> +#endif
> +
> +/* @mask bits for statmount(2) */
> +#define STATMOUNT_SB_BASIC 0x00000001U /* Want/got sb_... */
> +#define STATMOUNT_MNT_BASIC 0x00000002U /* Want/got mnt_... */
> +#define STATMOUNT_PROPAGATE_FROM 0x00000004U /* Want/got propagate_from */
> +#define STATMOUNT_MNT_ROOT 0x00000008U /* Want/got mnt_root */
> +#define STATMOUNT_MNT_POINT 0x00000010U /* Want/got mnt_point */
> +#define STATMOUNT_FS_TYPE 0x00000020U /* Want/got fs_type */
> +#define STATMOUNT_MNT_NS_ID 0x00000040U /* Want/got mnt_ns_id */
> +#define STATMOUNT_MNT_OPTS 0x00000080U /* Want/got mnt_opts */
> +
> +#define STATX_MNT_ID_UNIQUE 0x00004000U /* Want/got extended stx_mount_id */
> +
> +struct statmount {
> + __u32 size;
> + __u32 mnt_opts;
> + __u64 mask;
> + __u32 sb_dev_major;
> + __u32 sb_dev_minor;
> + __u64 sb_magic;
> + __u32 sb_flags;
> + __u32 fs_type;
> + __u64 mnt_id;
> + __u64 mnt_parent_id;
> + __u32 mnt_id_old;
> + __u32 mnt_parent_id_old;
> + __u64 mnt_attr;
> + __u64 mnt_propagation;
> + __u64 mnt_peer_group;
> + __u64 mnt_master;
> + __u64 propagate_from;
> + __u32 mnt_root;
> + __u32 mnt_point;
> + __u64 mnt_ns_id;
> + __u64 __spare2[49];
> + char str[];
> +};
> +
> +struct mnt_id_req {
> + __u32 size;
> + __u32 spare;
> + __u64 mnt_id;
> + __u64 param;
> + __u64 mnt_ns_id;
> +};
> +
> +#define MNT_ID_REQ_SIZE_VER1 32 /* sizeof second published struct */
> +
> +#define LSMT_ROOT 0xffffffffffffffff /* root mount */
> +
> +static int __statmount(__u64 mnt_id, __u64 mnt_ns_id, __u64 mask,
> + struct statmount *stmnt, size_t bufsize,
> + unsigned int flags)
> +{
> + struct mnt_id_req req = {
> + .size = MNT_ID_REQ_SIZE_VER1,
> + .mnt_id = mnt_id,
> + .param = mask,
> + .mnt_ns_id = mnt_ns_id,
> + };
> +
> + return syscall(__NR_statmount, &req, stmnt, bufsize, flags);
> +}
> +
> +static struct statmount *sys_statmount(__u64 mnt_id, __u64 mnt_ns_id,
> + __u64 mask, unsigned int flags)
> +{
> + size_t bufsize = 1 << 15;
> + struct statmount *stmnt = NULL, *tmp = NULL;
> + int ret;
> +
> + for (;;) {
> + tmp = realloc(stmnt, bufsize);
> + if (!tmp)
> + goto out;
> +
> + stmnt = tmp;
> + ret = __statmount(mnt_id, mnt_ns_id, mask, stmnt, bufsize, flags);
> + if (!ret)
> + return stmnt;
> +
> + if (errno != EOVERFLOW)
> + goto out;
> +
> + bufsize <<= 1;
> + if (bufsize >= UINT_MAX / 2)
> + goto out;
> + }
> +
> +out:
> + free(stmnt);
> + return NULL;
> +}
> +
> +static ssize_t sys_listmount(__u64 mnt_id, __u64 last_mnt_id, __u64 mnt_ns_id,
> + __u64 list[], size_t num, unsigned int flags)
> +{
> + struct mnt_id_req req = {
> + .size = MNT_ID_REQ_SIZE_VER1,
> + .mnt_id = mnt_id,
> + .param = last_mnt_id,
> + .mnt_ns_id = mnt_ns_id,
> + };
> +
> + return syscall(__NR_listmount, &req, list, num, flags);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +#define LISTMNT_BUFFER 10
> + __u64 list[LISTMNT_BUFFER], last_mnt_id = 0;
> + int ret, pidfd, fd_mntns;
> + struct mnt_ns_info info = {};
> +
> + pidfd = sys_pidfd_open(getpid(), 0);
> + if (pidfd < 0)
> + die_errno("pidfd_open failed");
> +
> + fd_mntns = ioctl(pidfd, PIDFD_GET_MNT_NAMESPACE, 0);
> + if (fd_mntns < 0)
> + die_errno("ioctl(PIDFD_GET_MNT_NAMESPACE) failed");
> +
> + ret = ioctl(fd_mntns, NS_MNT_GET_INFO, &info);
> + if (ret < 0)
> + die_errno("ioctl(NS_GET_MNTNS_ID) failed");
> +
> + printf("Listing %u mounts for mount namespace %llu\n",
> + info.nr_mounts, info.mnt_ns_id);
> + for (;;) {
> + ssize_t nr_mounts;
> +next:
> + nr_mounts = sys_listmount(LSMT_ROOT, last_mnt_id,
> + info.mnt_ns_id, list, LISTMNT_BUFFER,
> + 0);
> + if (nr_mounts <= 0) {
> + int fd_mntns_next;
> +
> + printf("Finished listing %u mounts for mount namespace %llu\n\n",
> + info.nr_mounts, info.mnt_ns_id);
> + fd_mntns_next = ioctl(fd_mntns, NS_MNT_GET_NEXT, &info);
> + if (fd_mntns_next < 0) {
> + if (errno == ENOENT) {
> + printf("Finished listing all mount namespaces\n");
> + exit(0);
> + }
> + die_errno("ioctl(NS_MNT_GET_NEXT) failed");
> + }
> + close(fd_mntns);
> + fd_mntns = fd_mntns_next;
> + last_mnt_id = 0;
> + printf("Listing %u mounts for mount namespace %llu\n",
> + info.nr_mounts, info.mnt_ns_id);
> + goto next;
> + }
> +
> + for (size_t cur = 0; cur < nr_mounts; cur++) {
> + struct statmount *stmnt;
> +
> + last_mnt_id = list[cur];
> +
> + stmnt = sys_statmount(last_mnt_id, info.mnt_ns_id,
> + STATMOUNT_SB_BASIC |
> + STATMOUNT_MNT_BASIC |
> + STATMOUNT_MNT_ROOT |
> + STATMOUNT_MNT_POINT |
> + STATMOUNT_MNT_NS_ID |
> + STATMOUNT_MNT_OPTS |
> + STATMOUNT_FS_TYPE, 0);
> + if (!stmnt) {
> + printf("Failed to statmount(%llu) in mount namespace(%llu)\n",
> + last_mnt_id, info.mnt_ns_id);
> + continue;
> + }
> +
> + 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",
> + stmnt->mnt_id,
> + stmnt->mnt_parent_id,
> + stmnt->str + stmnt->fs_type,
> + stmnt->str + stmnt->mnt_root,
> + stmnt->str + stmnt->mnt_point,
> + stmnt->str + stmnt->mnt_opts);
> + free(stmnt);
> + }
> + }
> +
> + exit(0);
> +}
>
Note that this replicates a lot of the functionality of the "mountinfo"
program. You could also extend that program with a different output
format instead of adding a new one.
--
Jeff Layton <jlayton@xxxxxxxxxx>
