freebsd-dev/lib/libc/gen/getvfsent.3

.\" $FreeBSD$
.\"	Written by Garrett A. Wollman, September 1994.
.\"	This manual page is in the public domain.
.\"
.Dd September 24, 1994
.Dt GETVFSENT 3
.Os
.Sh NAME
.Nm getvfsent ,
.Nm setvfsent ,
.Nm endvfsent ,
.Nm vfsisloadable ,
.Nm vfsload
.Nd manage virtual filesystem modules
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/mount.h>
.Ft struct ovfsconf *
.Fn getvfsent "void"
.Ft void
.Fn setvfsent "int cachelist"
.Ft void
.Fn endvfsent "void"
.Ft int
.Fn vfsisloadable "const char *name"
.Ft int
.Fn vfsload "const char *name"
.Sh DESCRIPTION
The
.Fn getvfsent
function provides convenient access to a list of installed virtual
filesystem modules managed by the kernel.  It steps through the
list of filesystems one at a time.  A null pointer is returned when
no more data is available.  The fields in a
.Dq Li struct ovfsconf
are as follows:
.Pp
.Bl -tag -compact -width vfc_refcount
.It vfc_name
the name of the filesystem
.It vfc_index
the filesystem type number assigned by the kernel and used in calls to
.Xr mount 2
.It vfc_refcount
the number of references to this filesystem
(usually the number of mounts, but one greater for filesystems which
cannot be unloaded or which are statically linked into the kernel)
.It vfc_flags
flag bits, of which none are currently defined
.El
.Pp
The
.Fn setvfsent
and
.Fn endvfsent
functions are used to control caching of the filesystem list, which is
obtained in toto from the kernel via
.Xr sysctl 3 .
If the
.Fa cachelist
parameter to
.Fn setvfsent
is non-zero, the list will be retrieved only once, upon the first call
to one of the retrieval functions, until
.Fn endvfsent
is called to clear the cache.  In general,
.Fn setvfsent 1
should be called by programs using the
.Fn getvfsent
function, and
.Fn setvfsent 0
(which is also the default state)
should be called by programs using the
.Fn vfsload
function.
.Pp
The
.Fn vfsisloadable
function returns a non-zero value if a later call to
.Fn vfsload name
is likely to succeed.  We say 
.Dq likely
because
.Fn vfsisloadable
does not check any of the conditions necessary for
.Fn vfsload
to succeed.
.Pp
The
.Fn vfsload
function attempts to load a kernel module implementing filesystem
.Fa name .
It returns zero if the filesystem module was successfully located and
loaded, or non-zero otherwise.  It should only be called in the
following circumstances:
.Bl -enum
.It
.Fn getvfsbyname
has been called and returned a non-zero value.
.It
.Fn vfsisloadable
has been called and returned a non-zero value.
.El
.Pp
Here is an example, taken from the source to
.Xr mount_cd9660 8 :
.Bd -literal -offset indent

struct vfsconf *vfc;
int error;

/* setup code here */

error = getvfsbyname("cd9660", &vfc);
if (error && vfsisloadable("cd9660")) {
	if (vfsload("cd9660"))
		err(EX_OSERR, "vfsload(cd9660)");
	endvfsent();	/* flush cache */
	error = getvfsbyname("cd9660", &vfc);
}
if (error)
	errx(1, "cd9660 filesystem is not available");

if (mount(vfc.vfc_name, dir, mntflags, &args) < 0)
	err(1, NULL);

.Ed
.Sh RETURN VALUES
The
.Fn getvfsent
routine returns a pointer to a static data structure when
it succeeds, and returns a null pointer when it fails.  On failure,
.Va errno
may be set to one of the values documented for
.Xr sysctl 3
or
.Xr malloc 3 ,
if a failure of that function was the cause; otherwise
.Va errno
will be unmodified.
.Pp
The
.Fn vfsload
function returns a non-zero value on failure, or zero on success.  If
.Fn vfsload
fails,
.Va errno
may be set to one of the values documented for
.Xr kldload 2 .
.Sh SEE ALSO
.Xr kldload 2 ,
.Xr mount 2 ,
.Xr mount 8
.Sh AUTHORS
The loadable filesystem support was written by
.An Garrett A. Wollman ,
based on generic loadable kernel module support by
.An Terry Lambert .
.Sh HISTORY
The
.Fn getvfsent
family of functions first appeared in
.Fx 2.0 .