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Need here to keep control device opened while there is 'any' dso
plugin loaded - otherwise there would a race closing controlfd
inside lvm2 plugin while some other monitoring thread would
tried to execute another WAITEVENT task.
Move all DSO related function in front, so they could be easily
referenced from rest of code.
Add proper error paths with logging and error reporting.
Drop mutex locking when releasing DSO - since DSO is always
allocated and released in main 'event' processing thread.
Respect lvm2_log_fn prototype. The idea of 'reusing' print_log with
plain cast is causing very strange crashes with some older 'gcc' compilers.
So just do it cleanly...
Rework thread creation code to better use resources.
New code will not leak 'timeout' registered thread on error path.
Also if the thread already exist - avoid creation of thread
object and it's later destruction.
If the race is noticed during adding new monitoring thread,
such thread is put on cleanup list and -EEXIST is reported.
As we now use 'unified' logging macro system - we no longer need
to protect from change of logging function pointer - it's set
once at the start of dmeventd and not change anymore
(as lvm2 library no longer interferers here).
There are reports of unexplained ioctl failures when using dmeventd.
An explanation might be that the wrong value of errno is being used.
Change libdevmapper to store an errno set by from dm ioctl() directly
and provide it to the caller through a new dm_task_get_errno() function.
[Replaced f9510548667754d9209b232348ccd2d806c0f1d8]
When responding to DM_EVENT_CMD_GET_REGISTERED_DEVICE no longer
ignore threads that have already been unregistered but which
are still present.
This means the caller can unregister a device and poll dmeventd
to ensure the monitoring thread has gone away before removing
the device. If a device was registered and unregistered in quick
succession and then removed, WAITEVENT could run in parallel with
the REMOVE.
Threads are moved to the _thread_registry_unused list when they
are unregistered.
Switch to allocate buffer from heap, since it might be potentially
bigger when extremaly large set of volumes would be monitored.
In case of allocation failure send ENOMEM message.
Also implicitelly ignore msg->size when msg->data is NULL.
When the last entry in the timeout queue is unregistered,
wakeup sleeping condition, so the thread is deleted earlier.
So the thread resource is release earlier.
Also when monitored with tools like valgrind this eliminites reported
leak.
Individual events are handled through separate threads,
so once we have more then a single thread in this eventwait
sleeping, we got race on the dm_log setting, since
if one event is timeout out on alarm, while another is still waiting,
then dm log has been restored to NULL and the next sigalarm
has been reported as error.
Fix it by introducing counter which is protected via mutex,
and only when the last event is released, logging is restored.
TODO: libdm seems to have some static vars which may audit
for this type of use.
The DM_EVENT_GET_PARAMETERS requests the parameters under which
the running dmeventd is run and the it sends them to caller.
The parameters sent:
- the pid of the running dmeventd
- foreground state
- exec_method (currently either "direct" or "systemd")
The exact message sent back:
pid=<pid> daemon=<no/yes> exec_method=<direct/systemd>
Trying to restart dmeventd as a reload action is causing problems
under systemd environment. The systemd loses track of new dmeventd
this way. See also https://bugzilla.redhat.com/show_bug.cgi?id=1060134
for more info.
We need to call dmeventd -R directly instead of "systemctl reload dm-event.service"
that was used before (the reload is aimed at configuration reload anyway,
not stateful restart of the daemon - we did this before just because
there's no ExecRestart in systemd and there's only ExecStart and
ExecStop with which we'd lose the state).
Also, use ExecStart="dmeventd -f" to run dmeventd in foreground
(and let's rely on systemd to daemonize it) and change the
service type from "forking" to "simple".
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.
