2008-04-30 17:10:46 +04:00
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.\" $NetBSD: vfs_hooks.9,v 1.4 2008/04/30 13:10:59 martin Exp $
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Apply the NFS exports list rototill patch:
- Remove all NFS related stuff from file system specific code.
- Drop the vfs_checkexp hook and generalize it in the new nfs_check_export
function, thus removing redundancy from all file systems.
- Move all NFS export-related stuff from kern/vfs_subr.c to the new
file sys/nfs/nfs_export.c. The former was becoming large and its code
is always compiled, regardless of the build options. Using the latter,
the code is only compiled in when NFSSERVER is enabled. While doing this,
also make some functions in nfs_subs.c conditional to NFSSERVER.
- Add a new command in nfssvc(2), called NFSSVC_SETEXPORTSLIST, that takes a
path and a set of export entries. At the moment it can only clear the
exports list or append entries, one by one, but it is done in a way that
allows setting the whole set of entries atomically in the future (see the
comment in mountd_set_exports_list or in doc/TODO).
- Change mountd(8) to use the nfssvc(2) system call instead of mount(2) so
that it becomes file system agnostic. In fact, all this whole thing was
done to remove a 'XXX' block from this utility!
- Change the mount*, newfs and fsck* userland utilities to not deal with NFS
exports initialization; done internally by the kernel when initializing
the NFS support for each file system.
- Implement an interface for VFS (called VFS hooks) so that several kernel
subsystems can run arbitrary code upon receipt of specific VFS events.
At the moment, this only provides support for unmount and is used to
destroy NFS exports lists from the file systems being unmounted, though it
has room for extension.
Thanks go to yamt@, chs@, thorpej@, wrstuden@ and others for their comments
and advice in the development of this patch.
2005-09-23 16:10:31 +04:00
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.\"
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.\" Copyright (c) 2005 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Julio M. Merino Vidal.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd September 23, 2005
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.Dt VFS_HOOKS 9
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.Os
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.Sh NAME
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.Nm vfs_hooks ,
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.Nm vfs_hooks_unmount
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.Nd VFS hooks interface
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/mount.h
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.Ft void
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.Fn vfs_hooks_unmount "struct mount *mp"
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.Sh DESCRIPTION
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The VFS hooks interface provides a way for different kernel subsystems to
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attach custom functions to specific VFS operations.
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This enforces code separation by keeping the VFS's core sources uncluttered
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and makes all subsystem functionality reside in a single place.
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As an example, this interface is used by the NFS server code to automatically
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handle the exports list for each mount point.
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.Pp
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Hooks are described by a
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.Ft struct vfs_hooks
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object, as seen below:
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.Bd -literal
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struct vfs_hooks {
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int (*vh_unmount)(struct mount *);
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};
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.Ed
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.Pp
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For simplicity, each field is named after the VFS operation it refers to.
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The purpose of each member function, alongside some important notes, is
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shown below:
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.Bl -tag -width compat
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.It Fn vh_unmount "mp"
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This hook is executed during the unmount process of a file system.
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.El
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.Pp
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For more information about the purpose of each operation, see
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.Xr vfsops 9 .
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Note that any of these fields may be a null pointer.
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.Pp
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After the definition of a
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.Ft struct vfs_hooks
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object, the kernel has to add it to the
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2005-09-24 00:29:08 +04:00
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.Va vfs_hooks
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Apply the NFS exports list rototill patch:
- Remove all NFS related stuff from file system specific code.
- Drop the vfs_checkexp hook and generalize it in the new nfs_check_export
function, thus removing redundancy from all file systems.
- Move all NFS export-related stuff from kern/vfs_subr.c to the new
file sys/nfs/nfs_export.c. The former was becoming large and its code
is always compiled, regardless of the build options. Using the latter,
the code is only compiled in when NFSSERVER is enabled. While doing this,
also make some functions in nfs_subs.c conditional to NFSSERVER.
- Add a new command in nfssvc(2), called NFSSVC_SETEXPORTSLIST, that takes a
path and a set of export entries. At the moment it can only clear the
exports list or append entries, one by one, but it is done in a way that
allows setting the whole set of entries atomically in the future (see the
comment in mountd_set_exports_list or in doc/TODO).
- Change mountd(8) to use the nfssvc(2) system call instead of mount(2) so
that it becomes file system agnostic. In fact, all this whole thing was
done to remove a 'XXX' block from this utility!
- Change the mount*, newfs and fsck* userland utilities to not deal with NFS
exports initialization; done internally by the kernel when initializing
the NFS support for each file system.
- Implement an interface for VFS (called VFS hooks) so that several kernel
subsystems can run arbitrary code upon receipt of specific VFS events.
At the moment, this only provides support for unmount and is used to
destroy NFS exports lists from the file systems being unmounted, though it
has room for extension.
Thanks go to yamt@, chs@, thorpej@, wrstuden@ and others for their comments
and advice in the development of this patch.
2005-09-23 16:10:31 +04:00
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link set using the
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.Fn VFS_HOOKS_ATTACH "struct vfs_hooks *"
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macro.
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.Pp
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Please note that this interface is incomplete on purpose to keep it in its
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smallest possible size (i.e., do not provide a hook that is not used).
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If you feel the need to hook a routine to a VFS operation that is not yet
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supported by this interface, just add it to the files described in
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.Sx CODE REFERENCES .
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.Sh FUNCTIONS
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The following functions are provided to the VFS code to run the hooked
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functions:
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.Bl -tag -width compact
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.It Fn vfs_hooks_unmount "mp"
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Runs all hooks for the VFS unmount operation.
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Given that these operations shall not fail, it returns
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.Ft void .
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2006-01-17 01:05:21 +03:00
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.El
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Apply the NFS exports list rototill patch:
- Remove all NFS related stuff from file system specific code.
- Drop the vfs_checkexp hook and generalize it in the new nfs_check_export
function, thus removing redundancy from all file systems.
- Move all NFS export-related stuff from kern/vfs_subr.c to the new
file sys/nfs/nfs_export.c. The former was becoming large and its code
is always compiled, regardless of the build options. Using the latter,
the code is only compiled in when NFSSERVER is enabled. While doing this,
also make some functions in nfs_subs.c conditional to NFSSERVER.
- Add a new command in nfssvc(2), called NFSSVC_SETEXPORTSLIST, that takes a
path and a set of export entries. At the moment it can only clear the
exports list or append entries, one by one, but it is done in a way that
allows setting the whole set of entries atomically in the future (see the
comment in mountd_set_exports_list or in doc/TODO).
- Change mountd(8) to use the nfssvc(2) system call instead of mount(2) so
that it becomes file system agnostic. In fact, all this whole thing was
done to remove a 'XXX' block from this utility!
- Change the mount*, newfs and fsck* userland utilities to not deal with NFS
exports initialization; done internally by the kernel when initializing
the NFS support for each file system.
- Implement an interface for VFS (called VFS hooks) so that several kernel
subsystems can run arbitrary code upon receipt of specific VFS events.
At the moment, this only provides support for unmount and is used to
destroy NFS exports lists from the file systems being unmounted, though it
has room for extension.
Thanks go to yamt@, chs@, thorpej@, wrstuden@ and others for their comments
and advice in the development of this patch.
2005-09-23 16:10:31 +04:00
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.Sh CODE REFERENCES
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The VFS hooks interface is implemented within the files
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.Pa sys/kern/vfs_hooks.c
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and
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.Pa sys/sys/mount.h .
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.Sh SEE ALSO
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.Xr intro 9 ,
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.Xr vfs 9 ,
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.Xr vfsops 9
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.Sh HISTORY
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The VFS hooks interface appeared in
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.Nx 4.0 .
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