David Teigland bf77f71711 lvmetad: add invalidation method ... Add the ability to invalidate global or individual VG metadata. The invalid state is returned to lvm commands along with the metadata. This allows lvm commands to detect stale metadata from the cache and reread the latest metadata from disk (in a subsequent patch.) These changes do not change the protocol or compatibility between lvm commands and lvmetad. Global information ------------------ Global information refers to metadata that is not isolated to a single VG , e.g. the list of vg names, or the list of pvs. When an external system, e.g. a locking system, detects that global information has been changed from another host (e.g. a new vg has been created) it sends lvmetad the message: set_global_info: global_invalid=1. lvmetad sets the global invalid flag to indicate that its cached data is stale. When lvm commands request information from lvmetad, lvmetad returns the cached information, along with an additional top-level config node called "global_invalid". This new info tells the lvm command that the cached information is stale. When an lvm command sees global_invalid from lvmated, it knows it should rescan devices and update lvmetad with the latest information. When this is complete, it sends lvmetad the message: set_global_info: global_invalid=0, and lvmetad clears the global invalid flag. Further lvm commands will use the lvmetad cache until it is invalidated again. The most common commands that cause global invalidation are vgcreate and vgextend. These are uncommon compared to commands that report global information, e.g. vgs. So, the percentage of lvmetad replies containing global_invalid should be very small. VG information -------------- VG information refers to metadata that is isolated to a single VG, e.g. an LV or the size of an LV. When an external system determines that VG information has been changed from another host (e.g. an lvcreate or lvresize), it sends lvmetad the message: set_vg_info: uuid=X version=N. X is the VG uuid, and N is the latest VG seqno that was written. lvmetad checks the seqno of its cached VG, and if the version from the message is newer, it sets an invalid flag for the cached VG. The invalid flag, along with the newer seqno are saved in a new vg_info struct. When lvm commands request VG metadata from lvmetad, lvmetad includes the invalid flag along with the VG metadata. The lvm command checks for this flag, and rereads the VG from disk if set. The VG read from disk is sent to lvmetad. lvmetad sees that the seqno in the new version matches the seqno from the last set_vg_info message, and clears the vg invalid flag. Further lvm commands will use the VG metadata from lvmetad until it is next invalidated.		2015-06-23 16:36:33 -05:00
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clvmd	makefiles: drop DEBUG mangling	2015-05-14 00:19:33 +02:00
cmirrord	pre-release	2014-11-11 14:13:00 +00:00
dmeventd	dmeventd: better debug	2015-06-15 14:46:44 +02:00
lvmetad	lvmetad: add invalidation method	2015-06-23 16:36:33 -05:00
lvmpolld	cleanup: drop double const	2015-06-15 14:46:44 +02:00
Makefile.in	lvmpolld: Add standalone polldaemon.	2015-05-09 00:59:18 +01:00