1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
3
4 =====
5 DLMFS
6 =====
7
8 A minimal DLM userspace interface implemented
9 system.
10
11 dlmfs is built with OCFS2 as it requires most
12
13 :Project web page: http://ocfs2.wiki.kernel
14 :Tools web page: https://github.com/markf
15 :OCFS2 mailing lists: https://subspace.kernel.
16
17 All code copyright 2005 Oracle except when oth
18
19 Credits
20 =======
21
22 Some code taken from ramfs which is Copyright
23 and Transmeta Corp.
24
25 Mark Fasheh <mark.fasheh@oracle.com>
26
27 Caveats
28 =======
29 - Right now it only works with the OCFS2 DLM,
30 DLM implementations should not be a major is
31
32 Mount options
33 =============
34 None
35
36 Usage
37 =====
38
39 If you're just interested in OCFS2, then pleas
40 rest of this document will be geared towards t
41 dlmfs for easy to setup and easy to use cluste
42 userspace.
43
44 Setup
45 =====
46
47 dlmfs requires that the OCFS2 cluster infrastr
48 place. Please download ocfs2-tools from the ab
49 cluster.
50
51 You'll want to start heartbeating on a volume
52 your lockspace can access. The easiest way to
53 ocfs2_hb_ctl (distributed with ocfs2-tools). R
54 that an OCFS2 file system be in place so that
55 find its heartbeat area, though it will eventu
56 against raw disks.
57
58 Please see the ocfs2_hb_ctl and mkfs.ocfs2 man
59 with ocfs2-tools.
60
61 Once you're heartbeating, DLM lock 'domains' c
62 destroyed and locks within them accessed.
63
64 Locking
65 =======
66
67 Users may access dlmfs via standard file syste
68 'libo2dlm' (distributed with ocfs2-tools) whic
69 system calls and presents a more traditional l
70
71 dlmfs handles lock caching automatically for t
72 request for an already acquired lock will not
73 call. Userspace programs are assumed to handle
74 locking.
75
76 Two levels of locks are supported - Shared Rea
77 Also supported is a Trylock operation.
78
79 For information on the libo2dlm interface, ple
80 distributed with ocfs2-tools.
81
82 Lock value blocks can be read and written to a
83 and write(2) against the fd obtained via your
84 maximum currently supported LVB length is 64 b
85 OCFS2 DLM limitation). Through this mechanism,
86 small amounts of data amongst their nodes.
87
88 mkdir(2) signals dlmfs to join a domain (which
89 as the resulting directory)
90
91 rmdir(2) signals dlmfs to leave the domain
92
93 Locks for a given domain are represented by re
94 domain directory. Locking against them is don
95 call.
96
97 The open(2) call will not return until your lo
98 an error has occurred, unless it has been inst
99 operation. If the lock succeeds, you'll get an
100
101 open(2) with O_CREAT to ensure the resource in
102 not automatically create inodes for existing l
103
104 ============ ===========================
105 Open Flag Lock Request Type
106 ============ ===========================
107 O_RDONLY Shared Read
108 O_RDWR Exclusive
109 ============ ===========================
110
111
112 ============ ===========================
113 Open Flag Resulting Locking Behavior
114 ============ ===========================
115 O_NONBLOCK Trylock operation
116 ============ ===========================
117
118 You must provide exactly one of O_RDONLY or O_
119
120 If O_NONBLOCK is also provided and the trylock
121 could not lock the resource then open(2) will
122
123 close(2) drops the lock associated with your f
124
125 Modes passed to mkdir(2) or open(2) are adhere
126 supported locally as well. This means you can
127 access to the resources via dlmfs on your loca
128
129 The resource LVB may be read from the fd in ei
130 Exclusive modes via the read(2) system call. I
131 write(2) only when open in Exclusive mode.
132
133 Once written, an LVB will be visible to other
134 Only or higher level locks on the resource.
135
136 See Also
137 ========
138 http://opendlm.sourceforge.net/cvsmirror/opend
139
140 For more information on the VMS distributed lo
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