1 uevents and GFS2 2 ================== 3 4During the lifetime of a GFS2 mount, a number of uevents are generated. 5This document explains what the events are and what they are used 6for (by gfs_controld in gfs2-utils). 7 8A list of GFS2 uevents 9----------------------- 10 111. ADD 12 13The ADD event occurs at mount time. It will always be the first 14uevent generated by the newly created filesystem. If the mount 15is successful, an ONLINE uevent will follow. If it is not successful 16then a REMOVE uevent will follow. 17 18The ADD uevent has two environment variables: SPECTATOR=[0|1] 19and RDONLY=[0|1] that specify the spectator status (a read-only mount 20with no journal assigned), and read-only (with journal assigned) status 21of the filesystem respectively. 22 232. ONLINE 24 25The ONLINE uevent is generated after a successful mount or remount. It 26has the same environment variables as the ADD uevent. The ONLINE 27uevent, along with the two environment variables for spectator and 28RDONLY are a relatively recent addition (2.6.32-rc+) and will not 29be generated by older kernels. 30 313. CHANGE 32 33The CHANGE uevent is used in two places. One is when reporting the 34successful mount of the filesystem by the first node (FIRSTMOUNT=Done). 35This is used as a signal by gfs_controld that it is then ok for other 36nodes in the cluster to mount the filesystem. 37 38The other CHANGE uevent is used to inform of the completion 39of journal recovery for one of the filesystems journals. It has 40two environment variables, JID= which specifies the journal id which 41has just been recovered, and RECOVERY=[Done|Failed] to indicate the 42success (or otherwise) of the operation. These uevents are generated 43for every journal recovered, whether it is during the initial mount 44process or as the result of gfs_controld requesting a specific journal 45recovery via the /sys/fs/gfs2/<fsname>/lock_module/recovery file. 46 47Because the CHANGE uevent was used (in early versions of gfs_controld) 48without checking the environment variables to discover the state, we 49cannot add any more functions to it without running the risk of 50someone using an older version of the user tools and breaking their 51cluster. For this reason the ONLINE uevent was used when adding a new 52uevent for a successful mount or remount. 53 544. OFFLINE 55 56The OFFLINE uevent is only generated due to filesystem errors and is used 57as part of the "withdraw" mechanism. Currently this doesn't give any 58information about what the error is, which is something that needs to 59be fixed. 60 615. REMOVE 62 63The REMOVE uevent is generated at the end of an unsuccessful mount 64or at the end of a umount of the filesystem. All REMOVE uevents will 65have been preceded by at least an ADD uevent for the same filesystem, 66and unlike the other uevents is generated automatically by the kernel's 67kobject subsystem. 68 69 70Information common to all GFS2 uevents (uevent environment variables) 71---------------------------------------------------------------------- 72 731. LOCKTABLE= 74 75The LOCKTABLE is a string, as supplied on the mount command 76line (locktable=) or via fstab. It is used as a filesystem label 77as well as providing the information for a lock_dlm mount to be 78able to join the cluster. 79 802. LOCKPROTO= 81 82The LOCKPROTO is a string, and its value depends on what is set 83on the mount command line, or via fstab. It will be either 84lock_nolock or lock_dlm. In the future other lock managers 85may be supported. 86 873. JOURNALID= 88 89If a journal is in use by the filesystem (journals are not 90assigned for spectator mounts) then this will give the 91numeric journal id in all GFS2 uevents. 92 934. UUID= 94 95With recent versions of gfs2-utils, mkfs.gfs2 writes a UUID 96into the filesystem superblock. If it exists, this will 97be included in every uevent relating to the filesystem. 98 99 100 101