1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt> 2 .. include:: <isonum.txt>
3 3
4 ===== 4 =====
5 DLMFS 5 DLMFS
6 ===== 6 =====
7 7
8 A minimal DLM userspace interface implemented 8 A minimal DLM userspace interface implemented via a virtual file
9 system. 9 system.
10 10
11 dlmfs is built with OCFS2 as it requires most 11 dlmfs is built with OCFS2 as it requires most of its infrastructure.
12 12
13 :Project web page: http://ocfs2.wiki.kernel 13 :Project web page: http://ocfs2.wiki.kernel.org
14 :Tools web page: https://github.com/markf 14 :Tools web page: https://github.com/markfasheh/ocfs2-tools
15 :OCFS2 mailing lists: https://subspace.kernel. 15 :OCFS2 mailing lists: https://subspace.kernel.org/lists.linux.dev.html
16 16
17 All code copyright 2005 Oracle except when oth 17 All code copyright 2005 Oracle except when otherwise noted.
18 18
19 Credits 19 Credits
20 ======= 20 =======
21 21
22 Some code taken from ramfs which is Copyright 22 Some code taken from ramfs which is Copyright |copy| 2000 Linus Torvalds
23 and Transmeta Corp. 23 and Transmeta Corp.
24 24
25 Mark Fasheh <mark.fasheh@oracle.com> 25 Mark Fasheh <mark.fasheh@oracle.com>
26 26
27 Caveats 27 Caveats
28 ======= 28 =======
29 - Right now it only works with the OCFS2 DLM, 29 - Right now it only works with the OCFS2 DLM, though support for other
30 DLM implementations should not be a major is 30 DLM implementations should not be a major issue.
31 31
32 Mount options 32 Mount options
33 ============= 33 =============
34 None 34 None
35 35
36 Usage 36 Usage
37 ===== 37 =====
38 38
39 If you're just interested in OCFS2, then pleas 39 If you're just interested in OCFS2, then please see ocfs2.txt. The
40 rest of this document will be geared towards t 40 rest of this document will be geared towards those who want to use
41 dlmfs for easy to setup and easy to use cluste 41 dlmfs for easy to setup and easy to use clustered locking in
42 userspace. 42 userspace.
43 43
44 Setup 44 Setup
45 ===== 45 =====
46 46
47 dlmfs requires that the OCFS2 cluster infrastr 47 dlmfs requires that the OCFS2 cluster infrastructure be in
48 place. Please download ocfs2-tools from the ab 48 place. Please download ocfs2-tools from the above url and configure a
49 cluster. 49 cluster.
50 50
51 You'll want to start heartbeating on a volume 51 You'll want to start heartbeating on a volume which all the nodes in
52 your lockspace can access. The easiest way to 52 your lockspace can access. The easiest way to do this is via
53 ocfs2_hb_ctl (distributed with ocfs2-tools). R 53 ocfs2_hb_ctl (distributed with ocfs2-tools). Right now it requires
54 that an OCFS2 file system be in place so that 54 that an OCFS2 file system be in place so that it can automatically
55 find its heartbeat area, though it will eventu 55 find its heartbeat area, though it will eventually support heartbeat
56 against raw disks. 56 against raw disks.
57 57
58 Please see the ocfs2_hb_ctl and mkfs.ocfs2 man 58 Please see the ocfs2_hb_ctl and mkfs.ocfs2 manual pages distributed
59 with ocfs2-tools. 59 with ocfs2-tools.
60 60
61 Once you're heartbeating, DLM lock 'domains' c 61 Once you're heartbeating, DLM lock 'domains' can be easily created /
62 destroyed and locks within them accessed. 62 destroyed and locks within them accessed.
63 63
64 Locking 64 Locking
65 ======= 65 =======
66 66
67 Users may access dlmfs via standard file syste 67 Users may access dlmfs via standard file system calls, or they can use
68 'libo2dlm' (distributed with ocfs2-tools) whic 68 'libo2dlm' (distributed with ocfs2-tools) which abstracts the file
69 system calls and presents a more traditional l 69 system calls and presents a more traditional locking api.
70 70
71 dlmfs handles lock caching automatically for t 71 dlmfs handles lock caching automatically for the user, so a lock
72 request for an already acquired lock will not 72 request for an already acquired lock will not generate another DLM
73 call. Userspace programs are assumed to handle 73 call. Userspace programs are assumed to handle their own local
74 locking. 74 locking.
75 75
76 Two levels of locks are supported - Shared Rea 76 Two levels of locks are supported - Shared Read, and Exclusive.
77 Also supported is a Trylock operation. 77 Also supported is a Trylock operation.
78 78
79 For information on the libo2dlm interface, ple 79 For information on the libo2dlm interface, please see o2dlm.h,
80 distributed with ocfs2-tools. 80 distributed with ocfs2-tools.
81 81
82 Lock value blocks can be read and written to a 82 Lock value blocks can be read and written to a resource via read(2)
83 and write(2) against the fd obtained via your 83 and write(2) against the fd obtained via your open(2) call. The
84 maximum currently supported LVB length is 64 b 84 maximum currently supported LVB length is 64 bytes (though that is an
85 OCFS2 DLM limitation). Through this mechanism, 85 OCFS2 DLM limitation). Through this mechanism, users of dlmfs can share
86 small amounts of data amongst their nodes. 86 small amounts of data amongst their nodes.
87 87
88 mkdir(2) signals dlmfs to join a domain (which 88 mkdir(2) signals dlmfs to join a domain (which will have the same name
89 as the resulting directory) 89 as the resulting directory)
90 90
91 rmdir(2) signals dlmfs to leave the domain 91 rmdir(2) signals dlmfs to leave the domain
92 92
93 Locks for a given domain are represented by re 93 Locks for a given domain are represented by regular inodes inside the
94 domain directory. Locking against them is don 94 domain directory. Locking against them is done via the open(2) system
95 call. 95 call.
96 96
97 The open(2) call will not return until your lo 97 The open(2) call will not return until your lock has been granted or
98 an error has occurred, unless it has been inst 98 an error has occurred, unless it has been instructed to do a trylock
99 operation. If the lock succeeds, you'll get an 99 operation. If the lock succeeds, you'll get an fd.
100 100
101 open(2) with O_CREAT to ensure the resource in 101 open(2) with O_CREAT to ensure the resource inode is created - dlmfs does
102 not automatically create inodes for existing l 102 not automatically create inodes for existing lock resources.
103 103
104 ============ =========================== 104 ============ ===========================
105 Open Flag Lock Request Type 105 Open Flag Lock Request Type
106 ============ =========================== 106 ============ ===========================
107 O_RDONLY Shared Read 107 O_RDONLY Shared Read
108 O_RDWR Exclusive 108 O_RDWR Exclusive
109 ============ =========================== 109 ============ ===========================
110 110
111 111
112 ============ =========================== 112 ============ ===========================
113 Open Flag Resulting Locking Behavior 113 Open Flag Resulting Locking Behavior
114 ============ =========================== 114 ============ ===========================
115 O_NONBLOCK Trylock operation 115 O_NONBLOCK Trylock operation
116 ============ =========================== 116 ============ ===========================
117 117
118 You must provide exactly one of O_RDONLY or O_ 118 You must provide exactly one of O_RDONLY or O_RDWR.
119 119
120 If O_NONBLOCK is also provided and the trylock 120 If O_NONBLOCK is also provided and the trylock operation was valid but
121 could not lock the resource then open(2) will 121 could not lock the resource then open(2) will return ETXTBUSY.
122 122
123 close(2) drops the lock associated with your f 123 close(2) drops the lock associated with your fd.
124 124
125 Modes passed to mkdir(2) or open(2) are adhere 125 Modes passed to mkdir(2) or open(2) are adhered to locally. Chown is
126 supported locally as well. This means you can 126 supported locally as well. This means you can use them to restrict
127 access to the resources via dlmfs on your loca 127 access to the resources via dlmfs on your local node only.
128 128
129 The resource LVB may be read from the fd in ei 129 The resource LVB may be read from the fd in either Shared Read or
130 Exclusive modes via the read(2) system call. I 130 Exclusive modes via the read(2) system call. It can be written via
131 write(2) only when open in Exclusive mode. 131 write(2) only when open in Exclusive mode.
132 132
133 Once written, an LVB will be visible to other 133 Once written, an LVB will be visible to other nodes who obtain Read
134 Only or higher level locks on the resource. 134 Only or higher level locks on the resource.
135 135
136 See Also 136 See Also
137 ======== 137 ========
138 http://opendlm.sourceforge.net/cvsmirror/opend 138 http://opendlm.sourceforge.net/cvsmirror/opendlm/docs/dlmbook_final.pdf
139 139
140 For more information on the VMS distributed lo 140 For more information on the VMS distributed locking API.
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