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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.
There are two reasons for this: first, this allows the client side to notice
that some PV has multiple devices associated with it and print appropriate
warnings. Second, if a duplicate device pops up and disappears, after this
change the original connection between the PV and device is not lost.
Free (and clear) h.protocol string on daemon_open() error paths
so it's OK for caller to skip calling daemon_close() if returned
h.socket_fd is -1.
Close h.socket_fd in daemon_close() to avoid possible leak.
https://bugzilla.redhat.com/1164234
"%d" in buffer_append_vf is 64 bit wide. Using just `int` for the
variable will fetch more from va_list than intended and shifting
remaining arguments resulting in errors like:
Internal error: Bad format string at '#orphan'
In cases where PV appears on a new device without disappearing from an old one
first, the device->pvid pointers could become ambiguous. This could cause the
ambiguous PV to be lost from the cache when a different PV comes up on one of
the ambiguous devices.
The PIE and RELRO compiler/linker options can be used to produce a code
some techniques applied that makes the code more immune to some attacks:
- PIE (Position Independent Executable). It can make use of the ASLR
(Address Space Layout Randomization) provided by kernel to avoid
static locations for .text regions of executables (this is the 'pie'
compiler and linker option)
- RELRO (Relocation Read-Only). This prevents overwrite attacks of
the GOT (Global Offset Table) and PLT (Procedure Lookup Table)
used for relocations by making it read-only after all relocations
are resolved (these are the 'relro' and 'now' linker options) -
hence all symbols are resolved at the very start so there's no
need for those tables to be writeable later.
These compiler/linker options are now used by default for daemons
if the compiler/linker supports it.
Make it easier to run a live lvmetad in debugging mode and
to avoid conflicts if multiple test instances need to be run
alongside a live one.
No longer require -s when -f is used: use built-in default.
Add -p to lvmetad to specify the pid file.
No longer disable pidfile if -f used to run in foreground.
If specified socket file appears to be genuine but stale, remove it
before use.
On error, only remove lvmetad socket file if created by the same
process. (Previous code removes socket even while a running instance
is using it!)
If using lv/vgchange --sysinit -aay and lvmetad is enabled, we'd like to
avoid the direct activation and rely on autoactivation instead so
it fits system initialization scripts.
But if we're calling lv/vgchange --sysinit -aay too early when even
lvmetad service is not started yet, we just need to do the direct
activation instead without printing any error messages (while
trying to connect to lvmetad and not finding its socket).
This patch adds two helper functions - "lvmetad_socket_present" and
"lvmetad_used" which can be used to check for this condition properly
and avoid these lvmetad connections when the socket is not present
(and hence lvmetad is not yet running).
The idea is to avoid a period when an existing VG is not mapped to either the
old or the new name. (Note that the brief "blackout" was present even if the
name did not actually change.) We instead allow a brief overlap of a VG existing
under both names, i.e. a query for a VG might succeed but before a lock is
acquired the VG disappears.
