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Documentation / filesystems / gfs2-uevents.txt




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Based on kernel version 3.9. Page generated on 2013-05-02 23:06 EST.

1	                              uevents and GFS2
2	                             ==================
3	
4	During the lifetime of a GFS2 mount, a number of uevents are generated.
5	This document explains what the events are and what they are used
6	for (by gfs_controld in gfs2-utils).
7	
8	A list of GFS2 uevents
9	-----------------------
10	
11	1. ADD
12	
13	The ADD event occurs at mount time. It will always be the first
14	uevent generated by the newly created filesystem. If the mount
15	is successful, an ONLINE uevent will follow.  If it is not successful
16	then a REMOVE uevent will follow.
17	
18	The ADD uevent has two environment variables: SPECTATOR=[0|1]
19	and RDONLY=[0|1] that specify the spectator status (a read-only mount
20	with no journal assigned), and read-only (with journal assigned) status
21	of the filesystem respectively.
22	
23	2. ONLINE
24	
25	The ONLINE uevent is generated after a successful mount or remount. It
26	has the same environment variables as the ADD uevent. The ONLINE
27	uevent, along with the two environment variables for spectator and
28	RDONLY are a relatively recent addition (2.6.32-rc+) and will not
29	be generated by older kernels.
30	
31	3. CHANGE
32	
33	The CHANGE uevent is used in two places. One is when reporting the
34	successful mount of the filesystem by the first node (FIRSTMOUNT=Done).
35	This is used as a signal by gfs_controld that it is then ok for other
36	nodes in the cluster to mount the filesystem.
37	
38	The other CHANGE uevent is used to inform of the completion
39	of journal recovery for one of the filesystems journals. It has
40	two environment variables, JID= which specifies the journal id which
41	has just been recovered, and RECOVERY=[Done|Failed] to indicate the
42	success (or otherwise) of the operation. These uevents are generated
43	for every journal recovered, whether it is during the initial mount
44	process or as the result of gfs_controld requesting a specific journal
45	recovery via the /sys/fs/gfs2/<fsname>/lock_module/recovery file.
46	
47	Because the CHANGE uevent was used (in early versions of gfs_controld)
48	without checking the environment variables to discover the state, we
49	cannot add any more functions to it without running the risk of
50	someone using an older version of the user tools and breaking their
51	cluster. For this reason the ONLINE uevent was used when adding a new
52	uevent for a successful mount or remount.
53	
54	4. OFFLINE
55	
56	The OFFLINE uevent is only generated due to filesystem errors and is used
57	as part of the "withdraw" mechanism. Currently this doesn't give any
58	information about what the error is, which is something that needs to
59	be fixed.
60	
61	5. REMOVE
62	
63	The REMOVE uevent is generated at the end of an unsuccessful mount
64	or at the end of a umount of the filesystem. All REMOVE uevents will
65	have been preceded by at least an ADD uevent for the same filesystem,
66	and unlike the other uevents is generated automatically by the kernel's
67	kobject subsystem.
68	
69	
70	Information common to all GFS2 uevents (uevent environment variables)
71	----------------------------------------------------------------------
72	
73	1. LOCKTABLE=
74	
75	The LOCKTABLE is a string, as supplied on the mount command
76	line (locktable=) or via fstab. It is used as a filesystem label
77	as well as providing the information for a lock_dlm mount to be
78	able to join the cluster.
79	
80	2. LOCKPROTO=
81	
82	The LOCKPROTO is a string, and its value depends on what is set
83	on the mount command line, or via fstab. It will be either
84	lock_nolock or lock_dlm. In the future other lock managers
85	may be supported.
86	
87	3. JOURNALID=
88	
89	If a journal is in use by the filesystem (journals are not
90	assigned for spectator mounts) then this will give the
91	numeric journal id in all GFS2 uevents.
92	
93	4. UUID=
94	
95	With recent versions of gfs2-utils, mkfs.gfs2 writes a UUID
96	into the filesystem superblock. If it exists, this will
97	be included in every uevent relating to the filesystem.
98	
99
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