1VFS_PREOPEN(8) System Administration tools VFS_PREOPEN(8)
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6 vfs_preopen - Hide read latencies for applications reading numbered
7 files
8
10 vfs objects = preopen
11
13 This VFS module is part of the samba(7) suite.
14 This module assists applications that want to read numbered files in
16 sequence with very strict latency requirements. One area where this
17 happens in video streaming applications that want to read one file per
18 frame.
19 When you use this module, a number of helper processes is started that
21 speculatively open files and read a number of bytes to prime the file
22 system cache, so that later on when the real application's request
23 comes along, no disk access is necessary.
24 This module is stackable.
26
28 preopen:posix-basic-regex = BOOL (default: no)
29 preopen:posix-basic-regex = yes changes the meaning of the
30 preopen:names option. Further details are described there.
31 preopen:names = /pattern1/pattern2/
33 preopen:names specifies the file name pattern(s) which should
34 trigger the preopen helpers to do their work. We assume that the
35 files are numbered incrementally. So if your file names are
36 numbered FRAME00000.frm FRAME00001.frm and so on you would list
37 them as preopen:names=/FRAME*.frm/. The default algorithm uses the
38 first (at least 3) digits it finds in order to calculate the name
39 of the next frames.
40 preopen:posix-basic-regex = yes changes the meaning of the
42 preopen:names option. It means 'POSIX Basic Regular Expression'
43 strings are used as patterns. The key is each pattern requires
44 exactly one 'subexpression' starting with '\(' and ending with '\)'
45 in order to specify the position of the digits representing the
46 incrementing frame numbers. Given a file names like
47 Movie7599Frame0v1234.txt, Movie7599Frame1v1234.txt,
48 Movie7599Frame2v1234.txt up to Movie7599Frame9v1234.txt you can use
49 preopen:names = /.*Frame\([0-9]\).*\.txt/ in order to match just a
50 single digits, this might not be a real world example, but it shows
51 the flexiblity that is possible here.
52 preopen:num_bytes = BYTES
54 Specifies the number of bytes the helpers should speculatively
55 read, defaults to 1.
56 preopen:helpers = NUM-PROCS
58 Number of forked helper processes, defaults to 1.
59 preopen:queuelen = NUM-FILES
61 Number of files that should be speculatively opened. Defaults to
62 the 10 subsequent files.
63 preopen:nomatch_log_level = LOGLEVEL
65 In order to debug or audit the usage of the preopen logic you can
66 use this option to specify at what log level details about
67 filenames not matching any pattern from 'preopen:names' are logged.
68 Defaults to the log level 5. See also smb.conf(5) in the 'log
70 level' section for special handling of the 'preopen' debug class.
71 preopen:match_log_level = LOGLEVEL
73 In order to debug or audit the usage of the preopen logic you can
74 use this option to specify at what log level details about
75 filenames actually matching a pattern from 'preopen:names' are
76 logged.
77 See also 'preopen:founddigits_log_level' and
79 'preopen:push_log_level'.
80 Defaults to the log level 5. See also smb.conf(5) in the 'log
82 level' section for special handling of the 'preopen' debug class.
83 preopen:nodigits_log_level = LOGLEVEL
85 In order to debug or audit problems with the preopen configuration
86 you can use this option to specify at what log level details about
87 filenames actually matching a pattern from 'preopen:names', but at
88 the same time don't contain the expected digits, are logged. This
89 is typically something the administrator wants to notice and adjust
90 the configuration in order to define more precisely where to find
91 the digits in the filename.
92 Defaults to the log level 1. See also smb.conf(5) in the 'log
94 level' section for special handling of the 'preopen' debug class.
95 preopen:founddigits_log_level = LOGLEVEL
97 In order to debug or audit the usage of the preopen logic you can
98 use this option to specify at what log level details about
99 filenames actually matching a pattern from 'preopen:names', and at
100 the same time having valid expected digits, are logged. This means
101 enough information is available in order to queue preopens.
102 Defaults to the log level 3. See also smb.conf(5) in the 'log
104 level' section for special handling of the 'preopen' debug class.
105 preopen:reset_log_level = LOGLEVEL
107 If a matching filename belongs to a different pattern from
108 'preopen:names', a different parent directory or differs in a
109 significant way from the last filename that was found before, the
110 module needs to reset it's internal queue state. This means that no
111 more preopens will be pushed to helper processes belonging to the
112 former queue state. In order to debug or audit such queue resets
113 you can use this option to specify at what log level details are
114 logged.
115 Defaults to the log level 5. See also smb.conf(5) in the 'log
117 level' section for special handling of the 'preopen' debug class.
118 preopen:push_log_level = LOGLEVEL
120 In order to debug or audit the usage of the preopen logic you can
121 use this option to specify at what log level details about
122 filenames actually pushed to preopen helper processes are logged.
123 This means they will actually be preopened soon.
124 Defaults to the log level 3. See also smb.conf(5) in the 'log
126 level' section for special handling of the 'preopen' debug class.
127 preopen:queue_log_level = LOGLEVEL
129 In order to debug details about internal queue processing you can
130 use this option to specify at what log level the details are
131 logged.
132 Defaults to the log level 10. See also smb.conf(5) in the 'log
134 level' section for special handling of the 'preopen' debug class.
135
137 This man page is part of version 4.18.9 of the Samba suite.
138
140 The original Samba software and related utilities were created by
141 Andrew Tridgell. Samba is now developed by the Samba Team as an Open
142 Source project similar to the way the Linux kernel is developed.
143 The PREOPEN VFS module was created with contributions from Volker
145 Lendecke and the developers at IBM.
146Samba 4.18.9 11/30/2023 VFS_PREOPEN(8)