KERNEL_MOUNT(9)

NAME
free_mntarg, kernel_mount, kernel_vmount, mount_arg, mount_argb, mount_argf, mount_argsu - functions provided as part of the kernel mount interface

SYNOPSIS
void
free_mntarg(struct mntarg *ma);
int
kernel_mount(struct mntarg *ma, int flags);
int
kernel_vmount(int flags, ...);
struct mntarg *
mount_arg(struct mntarg *ma, const char *name, const void *val, int len);
struct mntarg *
mount_argb(struct mntarg *ma, int flag, const char *name);
struct mntarg *
mount_argf(struct mntarg *ma, const char *name, const char *fmt, ...);
struct mntarg *
mount_argsu(struct mntarg *ma, const char *name, const void *val, int len);

DESCRIPTION
The kernel_mount() family of functions are provided as an API for building a list of mount arguments which will be used to mount file systems from inside the kernel. By accumulating a list of arguments, the API takes shape and provides the information necessary for the kernel to control the mount(8) utility. When an error occurs, the process will stop. This will not cause a panic(9).

The header of the structure is stored in src/sys/kern/vfs_mount.c which permits automatic structure creation to ease the mount process. Memory allocation must always be freed when the entire process is complete, it is an error otherwise.

The free_mntarg() function is used to free or clear the mntarg structure.

The kernel_mount() function pulls information from the structure to perform the mount request on a given file system. Additionally, the kernel_mount() function always calls the free_mntarg() function. If ma contains any error code generated during the construction, that code will be called and the file system mount will not be attempted.

The kernel_vmount() is a function similar to printf(9) which is used to mount a file system.

The mount_arg() function takes a plain argument and crafts parts of the structure with regards to various mount options. If the length is a value less than 0, strlen(3) is used. This argument will be referenced until either free_mntarg() or kernel_mount() is called.

The mount_argb() function is used to add boolean arguments to the structure. The flag is the boolean value and name must start with "no", otherwise a panic will occur.

The mount_argf() function adds printf(9) style arguments to the current structure.

The mount_argsu() function will add arguments to the structure from a userland string.

EXAMPLES
An example of the *_cmount() function:

    static int
    msdosfs_cmount(struct mntarg *ma, void *data, int flags, struct thread *td)
    {
    	struct msdosfs_args args;
    	int error;
    	if (data == NULL)
    		return (EINVAL);
    	error = copyin(data, &args, sizeof args);
    	if (error)
    		return (error);
    	ma = mount_argsu(ma, "from", args.fspec, MAXPATHLEN);
    	ma = mount_arg(ma, "export", &args.export, sizeof args.export);
    	ma = mount_argf(ma, "uid", "%d", args.uid);
    	ma = mount_argf(ma, "gid", "%d", args.gid);
    	ma = mount_argf(ma, "mask", "%d", args.mask);
    	ma = mount_argf(ma, "dirmask", "%d", args.dirmask);
    	ma = mount_argb(ma, args.flags & MSDOSFSMNT_SHORTNAME, "noshortname");
    	ma = mount_argb(ma, args.flags & MSDOSFSMNT_LONGNAME, "nolongname");
    	ma = mount_argb(ma, !(args.flags & MSDOSFSMNT_NOWIN95), "nowin95");
    	ma = mount_argb(ma, args.flags & MSDOSFSMNT_KICONV, "nokiconv");
    	ma = mount_argsu(ma, "cs_win", args.cs_win, MAXCSLEN);
    	ma = mount_argsu(ma, "cs_dos", args.cs_dos, MAXCSLEN);
    	ma = mount_argsu(ma, "cs_local", args.cs_local, MAXCSLEN);
    	error = kernel_mount(ma, flags);
    	return (error);
    }

When working with kernel_vmount(), varargs must come in pairs, e.g., {name, value}.

    	error = kernel_vmount(
    	    MNT_RDONLY,
    	    "fstype", vfsname,
    	    "fspath", "/",
    	    "from", path,
    	    NULL);

SEE ALSO
VFS(9), VFS_MOUNT(9), vfs_mount(9)

HISTORY
The kernel_mount() family of functions and this manual page first appeared in FreeBSD 6.0.

AUTHORS
-nosplit The kernel_mount() family of functions and API was developed by Poul-Henning Kamp <phk@FreeBSD.org>. This manual page was written by Tom Rhodes <trhodes@FreeBSD.org>.