167 lines
3.8 KiB
Groff
167 lines
3.8 KiB
Groff
.\" $FreeBSD$
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.\" Written by Garrett A. Wollman, September 1994.
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.\" This manual page is in the public domain.
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.\"
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.Dd September 24, 1994
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.Dt GETVFSENT 3
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.Os
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.Sh NAME
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.Nm getvfsent ,
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.Nm setvfsent ,
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.Nm endvfsent ,
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.Nm vfsisloadable ,
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.Nm vfsload
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.Nd manage virtual filesystem modules
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <sys/param.h>
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.Fd #include <sys/mount.h>
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.Ft struct ovfsconf *
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.Fn getvfsent "void"
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.Ft void
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.Fn setvfsent "int cachelist"
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.Ft void
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.Fn endvfsent "void"
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.Ft int
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.Fn vfsisloadable "const char *name"
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.Ft int
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.Fn vfsload "const char *name"
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.Sh DESCRIPTION
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The
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.Fn getvfsent
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function provides convenient access to a list of installed virtual
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filesystem modules managed by the kernel. It steps through the
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list of filesystems one at a time. A null pointer is returned when
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no more data is available. The fields in a
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.Dq Li struct ovfsconf
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are as follows:
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.Pp
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.Bl -tag -compact -width vfc_refcount
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.It vfc_name
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the name of the filesystem
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.It vfc_index
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the filesystem type number assigned by the kernel and used in calls to
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.Xr mount 2
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.It vfc_refcount
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the number of references to this filesystem
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(usually the number of mounts, but one greater for filesystems which
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cannot be unloaded or which are statically linked into the kernel)
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.It vfc_flags
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flag bits, of which none are currently defined
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.El
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.Pp
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The
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.Fn setvfsent
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and
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.Fn endvfsent
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functions are used to control caching of the filesystem list, which is
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obtained in toto from the kernel via
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.Xr sysctl 3 .
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If the
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.Fa cachelist
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parameter to
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.Fn setvfsent
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is non-zero, the list will be retrieved only once, upon the first call
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to one of the retrieval functions, until
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.Fn endvfsent
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is called to clear the cache. In general,
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.Fn setvfsent 1
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should be called by programs using the
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.Fn getvfsent
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function, and
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.Fn setvfsent 0
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(which is also the default state)
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should be called by programs using the
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.Fn vfsload
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function.
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.Pp
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The
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.Fn vfsisloadable
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function returns a non-zero value if a later call to
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.Fn vfsload name
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is likely to succeed. We say
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.Dq likely
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because
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.Fn vfsisloadable
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does not check any of the conditions necessary for
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.Fn vfsload
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to succeed.
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.Pp
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The
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.Fn vfsload
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function attempts to load a kernel module implementing filesystem
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.Fa name .
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It returns zero if the filesystem module was successfully located and
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loaded, or non-zero otherwise. It should only be called in the
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following circumstances:
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.Bl -enum
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.It
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.Fn getvfsbyname
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has been called and returned a non-zero value.
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.It
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.Fn vfsisloadable
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has been called and returned a non-zero value.
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.El
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.Pp
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Here is an example, taken from the source to
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.Xr mount_cd9660 8 :
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.Bd -literal -offset indent
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struct vfsconf *vfc;
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int error;
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/* setup code here */
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error = getvfsbyname("cd9660", &vfc);
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if (error && vfsisloadable("cd9660")) {
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if (vfsload("cd9660"))
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err(EX_OSERR, "vfsload(cd9660)");
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endvfsent(); /* flush cache */
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error = getvfsbyname("cd9660", &vfc);
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}
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if (error)
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errx(1, "cd9660 filesystem is not available");
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if (mount(vfc.vfc_name, dir, mntflags, &args) < 0)
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err(1, NULL);
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.Ed
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.Sh RETURN VALUES
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The
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.Fn getvfsent
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routine returns a pointer to a static data structure when
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it succeeds, and returns a null pointer when it fails. On failure,
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.Va errno
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may be set to one of the values documented for
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.Xr sysctl 3
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or
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.Xr malloc 3 ,
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if a failure of that function was the cause; otherwise
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.Va errno
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will be unmodified.
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.Pp
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The
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.Fn vfsload
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function returns a non-zero value on failure, or zero on success. If
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.Fn vfsload
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fails,
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.Va errno
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may be set to one of the values documented for
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.Xr kldload 2 .
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.Sh SEE ALSO
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.Xr kldload 2 ,
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.Xr mount 2 ,
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.Xr mount 8
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.Sh AUTHORS
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.An -nosplit
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The loadable filesystem support was written by
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.An Garrett A. Wollman ,
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based on generic loadable kernel module support by
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.An Terry Lambert .
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.Sh HISTORY
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The
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.Fn getvfsent
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family of functions first appeared in
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.Fx 2.0 .
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