vfs_fileid - Man Page

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 = 256

Version

This man page is part of version 4.17.3 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.

Info

11/21/2022 Samba 4.17.3 System Administration tools