Documentation/filesystems/autofs-mount-control.rst

Source file repositories/reference/linux-study-clean/Documentation/filesystems/autofs-mount-control.rst

File Facts

System
Linux kernel
Corpus path
Documentation/filesystems/autofs-mount-control.rst
Extension
.rst
Size
18544 bytes
Lines
411
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

struct autofs_dev_ioctl {
	    __u32 ver_major;
	    __u32 ver_minor;
	    __u32 size;             /* total size of data passed in
				    * including this struct */
	    __s32 ioctlfd;          /* automount command fd */

	    /* Command parameters */
	    union {
		    struct args_protover		protover;
		    struct args_protosubver		protosubver;
		    struct args_openmount		openmount;
		    struct args_ready		ready;
		    struct args_fail		fail;
		    struct args_setpipefd		setpipefd;
		    struct args_timeout		timeout;
		    struct args_requester		requester;
		    struct args_expire		expire;
		    struct args_askumount		askumount;
		    struct args_ismountpoint	ismountpoint;
	    };

	    char path[];
    };

The ioctlfd field is a mount point file descriptor of an autofs mount
point. It is returned by the open call and is used by all calls except
the check for whether a given path is a mount point, where it may
optionally be used to check a specific mount corresponding to a given
mount point file descriptor, and when requesting the uid and gid of the
last successful mount on a directory within the autofs file system.

The union is used to communicate parameters and results of calls made
as described below.

The path field is used to pass a path where it is needed and the size field
is used account for the increased structure length when translating the
structure sent from user space.

This structure can be initialized before setting specific fields by using
the void function call init_autofs_dev_ioctl(``struct autofs_dev_ioctl *``).

All of the ioctls perform a copy of this structure from user space to
kernel space and return -EINVAL if the size parameter is smaller than
the structure size itself, -ENOMEM if the kernel memory allocation fails
or -EFAULT if the copy itself fails. Other checks include a version check
of the compiled in user space version against the module version and a
mismatch results in a -EINVAL return. If the size field is greater than
the structure size then a path is assumed to be present and is checked to
ensure it begins with a "/" and is NULL terminated, otherwise -EINVAL is
returned. Following these checks, for all ioctl commands except
AUTOFS_DEV_IOCTL_VERSION_CMD, AUTOFS_DEV_IOCTL_OPENMOUNT_CMD and
AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD the ioctlfd is validated and if it is
not a valid descriptor or doesn't correspond to an autofs mount point
an error of -EBADF, -ENOTTY or -EINVAL (not an autofs descriptor) is
returned.


The ioctls
==========

An example of an implementation which uses this interface can be seen
in autofs version 5.0.4 and later in file lib/dev-ioctl-lib.c of the
distribution tar available for download from kernel.org in directory
/pub/linux/daemons/autofs/v5.

The device node ioctl operations implemented by this interface are:


AUTOFS_DEV_IOCTL_VERSION

Annotation

Implementation Notes