DragonFly On-Line Manual Pages

GETVFSENT(3)          DragonFly 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
     successfully 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
     unmodified.

     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
     documented for kldload(2).

SEE ALSO
     kldload(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.

DragonFly 4.3                 September 24, 1994                 DragonFly 4.3