https://bugzilla.redhat.com/show_bug.cgi?id=1276198

Prior to commit id '98322052' failure to saferead the block device would
cause an error to be logged and the device to be skipped while attempting
to discover/create a stable target path for a new LUN (NPIV).

This was because virStorageBackendSCSIFindLUs ignored errors from
processLU and virStorageBackendSCSINewLun.

Ignoring the failure allowed a multipath device with an "active" and
"ghost" to be present on the host with the "ghost" block device being
ignored. This patch will return a -2 to the caller indicating the desire
to ignore the block device since it cannot be used directly rather than
fail the pool startup.

I found this useful while processing a volume that wouldn't end up
showing up in the resulting list of block volumes. In this case, the
partition type wasn't found in the disk_types table.

Similar to the openflags VIR_STORAGE_VOL_OPEN_NOERROR processing, if some
read processing operation fails, check the readflags for the corresponding
error flag being set. If so, rather then causing an error - use VIR_WARN
to flag the error, but return -2 which some callers can use to perform
specific actions. Use a new VIR_STORAGE_VOL_READ_NOERROR flag in a new
VolReadErrorMode enum.

While processing the volume for lseek, virFileReadHeaderFD, and
virStorageFileGetMetadataFromBuf - failure would cause an error,
but ret would not be set. That would result in an error message being
sent, but successful status being returned.

Just so it's clearer what to expect upon input and what types of return
values could be generated.  These were loosely copied from existing
virStorageBackendUpdateVolTargetInfoFD.

Similar to the openflags which allow VIR_STORAGE_VOL_OPEN_NOERROR to be
passed to avoid open errors, add a 'readflags' variable so that in the
future read failures could also be ignored.

This updates the test program to make it consistent with recent changes
to the mock libraries, and also opens up the possibility of mocking more
than just /sys in the future.

Instead of fakesysfsdir, which is very generic, use fakesysfspcidir and
fakesysfscgroupdir. This makes it explicit what part of the fake sysfs
filesystem they're referring to, and also leaves open the possibility of
handling files in two unrelated parts of the fake sysfs filesystem.

No functional changes.

The old name is no longer accurate, since now we're using its value as
the root of the fake filesystem.

No functional changes.

We might need to mock files living outside SYSFS_PREFIX later on,
so it's better to treat the temporary directory we are passed via
the environment as the root of the fake filesystem and create
SYSFS_PREFIX inside it.

The environment variable name will be changed to reflect the new use
we're making of it in a later commit.

We might need to mock files living outside PCI_SYSFS_PREFIX later on,
so it's better to treat the temporary directory we are passed via
the environment as the root of the fake filesystem and create
PCI_SYSFS_PREFIX inside it.

The environment variable name will be changed to reflect the new use
we're making of it in a later commit.

init_env() will return right away if fakesysfsdir is already
initialized, so this check is redundant.

The test program is not preloading any of the mock libraries that read
that environment variable, so setting it is pointless.

Use the proper data structures for the iteration since ncpupids will be
made private later.

Change some of the control structures and switch to using the new vcpu
structure.

Instead of directly accessing the array add a helper to do this.

Add qemuDomainHasVCpuPids to do the checking and replace in place checks
with it.

We no longer need checking whether the thread contains fake data
(vcpupids[0] == vm->pid) as in b07f3d82
and 65686e5a this was removed.

The vCPU threads make sense in the counterparts that set the vCPU
bandwidth/quota, not in the emulator one. The emulator tunables are set
all the time anyways.

Drop the extra check and remove the now unneeded vm argument.

Since commit 0c04906f the check for priv->cgroup doesn't make sense as
the calls to virCgroupHasController return the same information. Remove
it and move it's comment partially to the new check.

The already spurious check was also later copied to the iothreads code.

Once more stuff will be moved into the vCPU data structure it will be
necessary to get a specific one in some ocasions. Add a helper that will
simplify this task.

Extract the checking code into a separate function and prepare the
infrastructure for checking the new structure type.

To allow collecting all relevant data at one place let's make def->vcpus
a structure and then we can start moving stuff into it.

Refactor the code flow so that 'exit_monitor:' can be removed.

This patch moves the auditing functions into places where it's certain
that hotunplug was or was not successful and reports errors from
qemuMonitorGetCPUInfo properly.

Refactor the code flow so that 'exit_monitor:' can be removed.

This patch also moves the auditing and setting of the new vCPU count
right to the place where the hotplug happens, since it's possible that
the hotplug succeeds and adds a cpu while other stuff fails.

Lastly, failures of qemuMonitorGetCPUInfo are now reported rather than
ignored. The function retuns 0 if it "successfully" detected 0 threads.

qemuDomainHotplugVcpus/qemuDomainHotunplugVcpus are complex enough in
regards of adding one CPU. Additionally it will be desired to reuse
those functions later with specific vCPU hotplug.

Move the loops for adding vCPUs into qemuDomainSetVcpusFlags so that the
helpers can be made simpler and more straightforward.

Let the function report errors internally and change it to return
standard return codes.

The cpu hotplug helper functions used negative error handling in a part
of them, although some code that was added later didn't properly set the
error codes in some cases. This would cause improper error messages in
cases where we couldn't modify the numa cpu mask and a few other cases.

Fix the logic by converting it to the regularly used pattern.

There's only very little common code among the two operations. Split the
functions so that the internals are easier to understand and refactor
later.

With a very unfortunate timing, the agent might vanish before we do the
second call while the locks were down. Re-check that the agent is
available before attempting it again.

Separate the code so that qemuDomainSetVcpusFlags contains only code
relevant to hardware hotplug/unplug.

As in commit 88dc7e0c, the helper can be used in cases where the
function actually does not access anyting in the private data besides
the agent.

Later on this will also be used to track size of the vcpu data array.
Use size_t so that we can utilize the memory allocation helpers.

Finalize the refactor by adding the 'virDomainDefGetVCpusMax' getter and
reusing it accross libvirt.

The new helper will simplify checking whether the domain config contains
inactive vCPUs.

The code can be unified into the new accessor rather than being
scattered accross the drivers.

Use the local variable rather than getting it all the time from the
struct. This will simplify further refactors.

To support further refactors replace all write access to def->maxvcpus
with a accessor function.