statmount - get a mount status

#include <linux/mount.h> /* Definition of STATMOUNT_* constants */
#include <unistd.h>
int syscall(SYS_statmount, struct mnt_id_req *req,
 struct statmount *smbuf, size_t bufsize,
 unsigned long flags);
#include <linux/mount.h>

struct mnt_id_req {
 __u32 size; /* sizeof(struct mnt_id_req) */
 __u64 mnt_id; /* The mnt_id being queried */
 __u64 param; /* An ORed combination of the STATMOUNT_ constants */
};
struct statmount {
 __u32 size;
 __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;
 char str[];
};

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

To access a mount's status, the caller must have CAP_SYS_ADMIN in the user namespace.

This function returns information about a mount, storing it in the buffer pointed to by smbuf. The returned buffer is a struct statmount which is of size bufsize with the fields filled in as described below. flags must be 0.

(Note that reserved space and padding is omitted.)

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 can be obtained from either statx(2) using STATX_MNT_ID_UNIQUE or from listmount(2) and is used as the identifier to query the status of the desired mount point.

req.param is used to tell the kernel which fields the caller is interested in. It is an ORed combination of the following constants

In general, the kernel does not reject values in req.param other than the above. (For an exception, see EINVAL in errors.) Instead, it simply informs the caller which values are supported by this kernel and filesystem via the statmount.mask field. Therefore, do not simply set req.param to UINT_MAX (all bits set), as one or more bits may, in the future, be used to specify an extension to the buffer.

The returned information

The status information for the target mount is returned in the statmount structure pointed to by smbuf.

The fields in the statmount structure are:

smbuf.size

The size of the returned smbuf structure, including any of the strings fields that were filled.

smbuf.mask

The ORed combination of STATMOUNT_* flags indicating which fields were filled in and thus valid. The kernel may return fields that weren't requested, and may fail to return fields that were requested, depending on what the backing file system and kernel supports. In either case, req.param will not be equal to mask.

smbuf.sb_dev_major
smbuf.sb_dev_minor

The device that is mounted at this mount point.

smbuf.sb_magic

The file system specific super block magic.

smbuf.sb_flags

The flags that are set on the super block, an ORed combination of SB_RDONLY, SB_SYNCHRONOUS, SB_DIRSYNC, SB_LAZYTIME.

smbuf.fs_type

The offset to the location in the smbuf.str buffer that contains the string representation of the mounted file system. It is a null-terminated string.

smbuf.mnt_id

The unique mount ID of the mount.

smbuf.mnt_parent_id

The unique mount ID of the parent mount point of this mount. If this is the root mount point then smbuf.mnt_id == smbuf.parent_mount_id.

smbuf.mnt_id_old

This corresponds to the mount ID that is exported by /proc/pid/mountinfo.

smbuf.mnt_parent_id_old

This corresponds to the parent mount ID that is exported by /proc/pid/mountinfo.

smbuf.mnt_attr

The MOUNT_ATTR_* flags set on this mount point.

smbuf.mnt_propagation

The mount propagation flags, which can be one of MS_SHARED, MS_SLAVE, MS_PRIVATE, MS_UNBINDABLE.

smbuf.mnt_peer_group

The ID of the shared peer group.

smbuf.mnt_master

The mount point receives its propagation from this mount ID.

smbuf.propagate_from

The ID from the namespace we propagated from.

smbuf.mnt_root

The offset to the location in the smbuf.str buffer that contains the string representation of the mount relative to the root of the file system. It is a null-terminated string.

smbuf.mnt_point

The offset to the location in the smbuf.str buffer that contains the string representation of the mount relative to the current root (ie if you are in a chroot). It is a null-terminated string.

On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error.

listmount(2), statx(2)