NAME

listmount - get a list of mount ID's

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <linux/mount.h>  /* Definition of struct mnt_id_req constants */
#include <unistd.h>

int syscall(SYS_listmount, struct mnt_id_req *req,
            uint64_t *mnt_ids, size_t nr_mnt_ids,
            unsigned long flags);

#include <linux/mount.h>

struct mnt_id_req {
    __u32  size;    /* sizeof(struct mnt_id_req) */
    __u64  mnt_id;  /* The parent mnt_id being searched */
    __u64  param;   /* The next mnt_id we want to find */
};

Note: glibc provides no wrapper for listmount(), necessitating the use of syscall(2).

DESCRIPTION

To access the mounts in your namespace, you must have CAP_SYS_ADMIN in the user namespace.

This function returns a list of mount IDs under the req.mnt_id. This is meant to be used in conjuction with statmount(2) in order to provide a way to iterate and discover mounted file systems.

The mnt_id_req structure

req.size is used by the kernel to determine which struct mnt_id_req is being passed in, it should always be set to sizeof(struct mnt_id_req).

req.mnt_id is the parent mnt_id that we will list from, which can either be LSMT_ROOT which means the root mount of the current mount namespace, or a mount ID obtained from either statx(2) using STATX_MNT_ID_UNIQUE or from listmount(2).

req.param is used to tell the kernel what mount ID to start the list from. This is useful if multiple calls to listmount(2) are required. This can be set to the last mount ID returned in order to resume from a previous spot in the list.

RETURN VALUE

On success, the number of entries filled into mnt_ids is returned; 0 if there are no more mounts left. On error, -1 is returned, and errno is set to indicate the error.

ERRORS

EPERM: Permission is denied for accessing this mount.
EFAULT: req or mnt_ids points to a location outside the process's accessible address space.
EINVAL: Invalid flag specified in flags.
EINVAL: req is of insufficient size to be utilized.
E2BIG: req is too large, the limit is the architectures page size.
ENOENT: The specified req.mnt_id doesn't exist.
ENOMEM: Out of memory (i.e., kernel memory).

STANDARDS

Linux.