VFS_PREOPEN(8) System Administration tools VFS_PREOPEN(8)

NAME

vfs_preopen - Hide read latencies for applications reading numbered
files

SYNOPSIS

vfs objects = preopen

DESCRIPTION

This VFS module is part of the samba(7) suite.

This module assists applications that want to read numbered files in
sequence with very strict latency requirements. One area where this
happens in video streaming applications that want to read one file
per frame.

When you use this module, a number of helper processes is started
that speculatively open files and read a number of bytes to prime the
file system cache, so that later on when the real application's
request comes along, no disk access is necessary.

This module is stackable.

OPTIONS

preopen:posix-basic-regex = BOOL (default: no)
preopen:posix-basic-regex = yes changes the meaning of the
preopen:names option. Further details are described there.

preopen:names = /pattern1/pattern2/
preopen:names specifies the file name pattern(s) which should
trigger the preopen helpers to do their work. We assume that the
files are numbered incrementally. So if your file names are
numbered FRAME00000.frm FRAME00001.frm and so on you would list
them as preopen:names=/FRAME*.frm/. The default algorithm uses
the first (at least 3) digits it finds in order to calculate the
name of the next frames.

preopen:posix-basic-regex = yes changes the meaning of the
preopen:names option. It means 'POSIX Basic Regular Expression'
strings are used as patterns. The key is each pattern requires
exactly one 'subexpression' starting with '\(' and ending with
'\)' in order to specify the position of the digits representing
the incrementing frame numbers. Given a file names like
Movie7599Frame0v1234.txt, Movie7599Frame1v1234.txt,
Movie7599Frame2v1234.txt up to Movie7599Frame9v1234.txt you can
use preopen:names = /.*Frame\([0-9]\).*\.txt/ in order to match
just a single digits, this might not be a real world example, but
it shows the flexiblity that is possible here.

preopen:num_bytes = BYTES
Specifies the number of bytes the helpers should speculatively
read, defaults to 1.

preopen:helpers = NUM-PROCS
Number of forked helper processes, defaults to 1.

preopen:queuelen = NUM-FILES
Number of files that should be speculatively opened. Defaults to
the 10 subsequent files.

preopen:nomatch_log_level = LOGLEVEL
In order to debug or audit the usage of the preopen logic you can
use this option to specify at what log level details about
filenames not matching any pattern from 'preopen:names' are
logged.

Defaults to the log level 5. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

preopen:match_log_level = LOGLEVEL
In order to debug or audit the usage of the preopen logic you can
use this option to specify at what log level details about
filenames actually matching a pattern from 'preopen:names' are
logged.

See also 'preopen:founddigits_log_level' and
'preopen:push_log_level'.

Defaults to the log level 5. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

preopen:nodigits_log_level = LOGLEVEL
In order to debug or audit problems with the preopen
configuration you can use this option to specify at what log
level details about filenames actually matching a pattern from
'preopen:names', but at the same time don't contain the expected
digits, are logged. This is typically something the administrator
wants to notice and adjust the configuration in order to define
more precisely where to find the digits in the filename.

Defaults to the log level 1. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

preopen:founddigits_log_level = LOGLEVEL
In order to debug or audit the usage of the preopen logic you can
use this option to specify at what log level details about
filenames actually matching a pattern from 'preopen:names', and
at the same time having valid expected digits, are logged. This
means enough information is available in order to queue preopens.

Defaults to the log level 3. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

preopen:reset_log_level = LOGLEVEL
If a matching filename belongs to a different pattern from
'preopen:names', a different parent directory or differs in a
significant way from the last filename that was found before, the
module needs to reset it's internal queue state. This means that
no more preopens will be pushed to helper processes belonging to
the former queue state. In order to debug or audit such queue
resets you can use this option to specify at what log level
details are logged.

Defaults to the log level 5. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

preopen:push_log_level = LOGLEVEL
In order to debug or audit the usage of the preopen logic you can
use this option to specify at what log level details about
filenames actually pushed to preopen helper processes are logged.
This means they will actually be preopened soon.

Defaults to the log level 3. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

preopen:queue_log_level = LOGLEVEL
In order to debug details about internal queue processing you can
use this option to specify at what log level the details are
logged.

Defaults to the log level 10. See also smb.conf(5) in the 'log
level' section for special handling of the 'preopen' debug class.

VERSION

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.

The PREOPEN VFS module was created with contributions from Volker
Lendecke and the developers at IBM.

Samba 4.18.11 03/13/2024 VFS_PREOPEN(8)