GETVFSENT(3) BSD Library Functions Manual GETVFSENT(3)NAME
getvfsent, setvfsent, endvfsent, vfsisloadable, vfsload — manage virtual
filesystem modules
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/param.h>
#include <sys/mount.h>
struct ovfsconf *
getvfsent(void);
void
setvfsent(int cachelist);
void
endvfsent(void);
int
vfsisloadable(const char *name);
int
vfsload(const char *name);
DESCRIPTION
The 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 “struct
ovfsconf” are as follows:
vfc_name the name of the filesystem
vfc_index the filesystem type number assigned by the kernel and used
in calls to mount(2)
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)
vfc_flags flag bits
The flags are defined as follows:
VFCF_STATIC statically compiled into kernel
VFCF_NETWORK may get data over the network
VFCF_READONLY writes are not implemented
VFCF_SYNTHETIC data does not represent real files
VFCF_LOOPBACK aliases some other mounted FS
VFCF_UNICODE stores file names as Unicode
The setvfsent() and endvfsent() functions are used to control caching of
the filesystem list, which is obtained in toto from the kernel via
sysctl(3). If the cachelist parameter to setvfsent() is non-zero, the
list will be retrieved only once, upon the first call to one of the
retrieval functions, until endvfsent() is called to clear the cache. In
general, setvfsent(1) should be called by programs using the getvfsent()
function, and setvfsent(0) (which is also the default state) should be
called by programs using the vfsload() function.
The vfsisloadable() function returns a non-zero value if a later call to
vfsload(name) is likely to succeed. We say “likely” because
vfsisloadable() does not check any of the conditions necessary for
vfsload() to succeed.
The vfsload() function attempts to load a kernel module implementing
filesystem name. It returns zero if the filesystem module was success‐
fully located and loaded, or non-zero otherwise. It should only be
called in the following circumstances:
1. getvfsbyname() has been called and returned a non-zero value.
2. vfsisloadable() has been called and returned a non-zero value.
Here is an example, taken from the source to mount_cd9660(8):
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);
RETURN VALUES
The getvfsent() routine returns a pointer to a static data structure when
it succeeds, and returns a null pointer when it fails. On failure, errno
may be set to one of the values documented for sysctl(3) or malloc(3), if
a failure of that function was the cause; otherwise errno will be unmodi‐
fied.
The vfsload() function returns a non-zero value on failure, or zero on
success. If vfsload() fails, errno may be set to one of the values docu‐
mented for kldload(2).
SEE ALSOkldload(2), mount(2), mount(8)HISTORY
The getvfsent() family of functions first appeared in FreeBSD 2.0.
AUTHORS
The loadable filesystem support was written by Garrett A. Wollman, based
on generic loadable kernel module support by Terry Lambert.
BSD September 24, 1994 BSD
