1 .. SPDX-License-Identifier: GPL-2.0 2 3 ================ 4 uevents and GFS2 5 ================ 6 7 During the lifetime of a GFS2 mount, a number of uevents are generated. 8 This document explains what the events are and what they are used 9 for (by gfs_controld in gfs2-utils). 10 11 A list of GFS2 uevents 12 ====================== 13 14 1. ADD 15 ------ 16 17 The ADD event occurs at mount time. It will always be the first 18 uevent generated by the newly created filesystem. If the mount 19 is successful, an ONLINE uevent will follow. If it is not successful 20 then a REMOVE uevent will follow. 21 22 The ADD uevent has two environment variables: SPECTATOR=[0|1] 23 and RDONLY=[0|1] that specify the spectator status (a read-only mount 24 with no journal assigned), and read-only (with journal assigned) status 25 of the filesystem respectively. 26 27 2. ONLINE 28 --------- 29 30 The ONLINE uevent is generated after a successful mount or remount. It 31 has the same environment variables as the ADD uevent. The ONLINE 32 uevent, along with the two environment variables for spectator and 33 RDONLY are a relatively recent addition (2.6.32-rc+) and will not 34 be generated by older kernels. 35 36 3. CHANGE 37 --------- 38 39 The CHANGE uevent is used in two places. One is when reporting the 40 successful mount of the filesystem by the first node (FIRSTMOUNT=Done). 41 This is used as a signal by gfs_controld that it is then ok for other 42 nodes in the cluster to mount the filesystem. 43 44 The other CHANGE uevent is used to inform of the completion 45 of journal recovery for one of the filesystems journals. It has 46 two environment variables, JID= which specifies the journal id which 47 has just been recovered, and RECOVERY=[Done|Failed] to indicate the 48 success (or otherwise) of the operation. These uevents are generated 49 for every journal recovered, whether it is during the initial mount 50 process or as the result of gfs_controld requesting a specific journal 51 recovery via the /sys/fs/gfs2/<fsname>/lock_module/recovery file. 52 53 Because the CHANGE uevent was used (in early versions of gfs_controld) 54 without checking the environment variables to discover the state, we 55 cannot add any more functions to it without running the risk of 56 someone using an older version of the user tools and breaking their 57 cluster. For this reason the ONLINE uevent was used when adding a new 58 uevent for a successful mount or remount. 59 60 4. OFFLINE 61 ---------- 62 63 The OFFLINE uevent is only generated due to filesystem errors and is used 64 as part of the "withdraw" mechanism. Currently this doesn't give any 65 information about what the error is, which is something that needs to 66 be fixed. 67 68 5. REMOVE 69 --------- 70 71 The REMOVE uevent is generated at the end of an unsuccessful mount 72 or at the end of a umount of the filesystem. All REMOVE uevents will 73 have been preceded by at least an ADD uevent for the same filesystem, 74 and unlike the other uevents is generated automatically by the kernel's 75 kobject subsystem. 76 77 78 Information common to all GFS2 uevents (uevent environment variables) 79 ===================================================================== 80 81 1. LOCKTABLE= 82 -------------- 83 84 The LOCKTABLE is a string, as supplied on the mount command 85 line (locktable=) or via fstab. It is used as a filesystem label 86 as well as providing the information for a lock_dlm mount to be 87 able to join the cluster. 88 89 2. LOCKPROTO= 90 ------------- 91 92 The LOCKPROTO is a string, and its value depends on what is set 93 on the mount command line, or via fstab. It will be either 94 lock_nolock or lock_dlm. In the future other lock managers 95 may be supported. 96 97 3. JOURNALID= 98 ------------- 99 100 If a journal is in use by the filesystem (journals are not 101 assigned for spectator mounts) then this will give the 102 numeric journal id in all GFS2 uevents. 103 104 4. UUID= 105 -------- 106 107 With recent versions of gfs2-utils, mkfs.gfs2 writes a UUID 108 into the filesystem superblock. If it exists, this will 109 be included in every uevent relating to the filesystem. 110 111 112
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