VFS_FILEID(8) System Administration tools VFS_FILEID(8)
NAME
vfs_fileid - Generates file_id structs with unique device id values
for cluster setups. It also adds ways to deliberately break lock
coherency for specific inodes
SYNOPSIS
vfs objects = fileid
DESCRIPTION
This VFS module is part of the
samba(7) suite.
Samba uses file_id structs to uniquely identify files for locking
purpose. By default the file_id contains the device and inode number
returned by the stat() system call. As the file_id is a unique
identifier of a file, it must be the same on all nodes in a cluster
setup. This module overloads the SMB_VFS_FILE_ID_CREATE() operation
and generates the device number based on the configured algorithm
(see the "fileid:algorithm" option).
When using the fsname or fsid algorithm a stat() and statfs() call is
required for all mounted file systems to generate the file_id. If
e.g. an NFS file system is unresponsive such a call might block and
the smbd process will become unresponsive. Use the "fileid:fstype
deny", "fileid:fstype allow", "fileid:mntdir deny", or "fileid:mntdir
allow" options to ignore potentially unresponsive file systems.
OPTIONS
fileid:algorithm = ALGORITHM
Available algorithms are fsname, fsid, next_module. The default
value is fsname. As well as the following legacy algorithms:
fsname_nodirs, fsname_norootdir, fsname_norootdir_ext and
hostname.
The fsname algorithm generates device id by hashing the kernel
device name.
The fsid algorithm generates the device id from the f_fsid
returned from the statfs() syscall.
The next_module algorithm lets the next vfs module in the module
chain generate the id. This is mainly used in combination with
the various 'nolock' features the fileid module provides.
The legacy hostname algorithm generates unique devid by hashing
the hostname and low level device id. It also implies
fileid:nolock_all_inodes=yes. This can be used to deliberately
break lock coherency in a cluster and with
fileid:nolock_max_slots also between local processes within a
node. NOTE: Do not use this without knowing what you are doing!
It breaks SMB semantics and it can lead to data corruption! This
implies fileid:nolock_all_inodes=yes.
The legacy fsname_nodirs algorithm is an alias for using the
fsname algorithm together with fileid:nolock_all_dirs=yes. NOTE:
Do not use this without knowing what you are doing! It breaks SMB
semantics! See fileid:nolock_paths for a more fine grained
approach.
The legacy fsname_norootdir algorithm is an alias for using the
fsname algorithm together with fileid:nolock_paths= ".". It means
this can be used to deliberately break lock coherency in a
cluster for the root directory of a share.
The legacy fsname_norootdir_ext algorithm is an alias for using
the fsname algorithm together with fileid:nolock_paths= "." and
fileid:nolock_max_slots = 18446744073709551615. It means this can
be used to deliberately break lock coherency completely for the
root directory of a share. Even local processes are no longer
lock coherent.
fileid:mapping = ALGORITHM
This option is the legacy version of the fileid:algorithm option,
which was used in earlier versions of fileid mapping feature in
custom Samba 3.0 versions.
fileid:fstype deny = LIST
List of file system types to be ignored for file_id generation.
fileid:fstype allow = LIST
List of file system types to be allowed for file_id generation.
If this option is set, file system types not listed here are
ignored.
fileid:mntdir deny = LIST
List of file system mount points to be ignored for file_id
generation.
fileid:mntdir allow = LIST
List of file system mount points to be allowed for file_id
generation. If this option is set, file system mount points not
listed here are ignored.
fileid:nolock_max_slots = NUMBER(1-18446744073709551615)
This option alters the behavior of the nolock algorithm in a ways
that it also breaks the lock coherency between individual
processes on the same host. The default is to have just 1
concurrent slot available per host. By incressing the number of
slots you can specify how many concurrent processes can work on a
given inode without contention, the number should typically be
larger than the a number of logical cpus, maybe 2 times of
num_cpus.
fileid:nolock_all_dirs = BOOL
This option triggers the use of the fileid nolock behavior for
all directory inodes, which can be used to deliberately break the
lock coherency for all directories. NOTE: Do not use this without
knowing what you are doing! It breaks SMB semantics! See
fileid:nolock_paths for a more fine grained approach.
fileid:nolock_all_inodes = BOOL
This option triggers the use of the fileid nolock algorithm for
all directoriy inode, which can be used to deliberately break the
lock coherency for all directories. NOTE: Do not use this without
knowing what you are doing! It breaks SMB semantics and it can
lead to data corruption! See fileid:nolock_paths for a more fine
grained approach.
fileid:nolock_paths = LIST
This option specifies a path list referring to files and/or
directories, which should use fileid nolock algorithm in order to
deliberately break the lock coherency for them. The specified
paths can be relative to the share root directory or absolute.
The names are case sensitive unix pathnames! Note all paths are
only evaluated at tree connect time, when the share is being
connected, from there on only the related device and inode
numbers from the stat() syscall are compared. Non existing paths
will generate a log level 0 message. NOTE: This option should be
used with care as it breaks SMB semantics! But it may help in
situation where a specific (commonly read-only) inode is highly
contended.
fileid:nolockinode = NUMBER
This legacy option triggers use of the fileid nolock behavior for
the configured inode, while ignoring and device id. This can be
used to deliberately break lock coherency for the corresponding
file or directory in a cluster. Using the fileid:nolock_paths
option is much more flexible and simpler to use.
EXAMPLES
Usage of the fileid module with the fsid algorithm:
[global] vfs objects = fileid fileid:algorithm = fsid Usage of the fileid module in order avoid load on heavily contended
(most likely read-only) inodes.
[global] vfs objects = fileid fileid:algorithm = next_module fileid:nolock_paths = . ContendedFolder1 /path/to/contended.exe fileid:nolock_max_slots = 256VERSION
This man page is part of version 4.18.11 of the Samba suite.
AUTHOR
The original Samba software and related utilities were created by
Andrew Tridgell. Samba is now developed by the Samba Team as an Open
Source project similar to the way the Linux kernel is developed.
Samba 4.18.11 03/13/2024 VFS_FILEID(8)
