freebsd-dev/share/man/man9/kernel_mount.9

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.Dd November 20, 2021
.Dt KERNEL_MOUNT 9
.Os
.Sh NAME
.Nm free_mntarg ,
.Nm kernel_mount ,
.Nm mount_arg ,
.Nm mount_argb ,
.Nm mount_argf ,
.Nm mount_argsu
.Nd "functions provided as part of the kernel mount interface"
.Sh SYNOPSIS
.Ft void
.Fn free_mntarg "struct mntarg *ma"
.Ft int
.Fn kernel_mount "struct mntarg *ma" "int flags"
.Ft "struct mntarg *"
.Fo mount_arg
.Fa "struct mntarg *ma" "const char *name" "const void *val" "int len"
.Fc
.Ft "struct mntarg *"
.Fn mount_argb "struct mntarg *ma" "int flag" "const char *name"
.Ft "struct mntarg *"
.Fn mount_argf "struct mntarg *ma" "const char *name" "const char *fmt" ...
.Ft "struct mntarg *"
.Fo mount_argsu
.Fa "struct mntarg *ma" "const char *name" "const void *val" "int len"
.Fc
.Sh DESCRIPTION
The
.Fn 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
.Xr mount 8
utility.
When an error occurs, the process will stop.
This will not cause a
.Xr panic 9 .
.Pp
The header of the structure is stored in
.Pa 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.
.Pp
The
.Fn free_mntarg
function is used to free or clear the
.Vt mntarg
structure.
.Pp
The
.Fn kernel_mount
function pulls information from the structure to perform
the mount request on a given file system.
Additionally, the
.Fn kernel_mount
function always calls the
.Fn free_mntarg
function.
If
.Fa ma
contains any error code generated during the construction,
that code will be called and the file system mount will
not be attempted.
.Pp
The
.Fn 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,
.Xr strlen 3
is used.
This argument will be referenced until either
.Fn free_mntarg
or
.Fn kernel_mount
is called.
.Pp
The
.Fn mount_argb
function is used to add boolean arguments to
the structure.
The
.Fa flag
is the boolean value and
.Fa name
must start with
.Qq Li no ,
otherwise a panic will occur.
.Pp
The
.Fn mount_argf
function adds
.Xr printf 9
style arguments to the current structure.
.Pp
The
.Fn mount_argsu
function will add arguments to the structure from a
userland string.
.Sh EXAMPLES
An example of the
.Fn *_cmount
function:
.Bd -literal
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);
}
.Ed
.Sh SEE ALSO
.Xr VFS 9 ,
.Xr VFS_MOUNT 9
.Sh HISTORY
The
.Fn kernel_mount
family of functions and this manual page first
appeared in
.Fx 6.0 .
.Sh AUTHORS
.An -nosplit
The
.Fn kernel_mount
family of functions and API was developed by
.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .
This manual page was written by
.An Tom Rhodes Aq Mt trhodes@FreeBSD.org .