Recent discussions have illustrated the potential for DOS attacks
with the hash table implementations used by most languages and
libraries.

   https://lwn.net/Articles/474912/

libvirt has an internal hash table impl, and uses hash tables for
a variety of purposes. The hash key generation code is pretty
simple and thus not strongly collision resistant.

This patch replaces the current libvirt hash key generator with
the (public domain) Murmurhash3 code. In addition every hash
table now gets a random seed value which is used to perturb the
hashing code. This should make it impossible to mount any
practical attack against libvirt hashing code.

* bootstrap.conf: Import bitrotate module
* src/Makefile.am: Add virhashcode.[ch]
* src/util/util.c: Make virRandom() return a fixed 32 bit
  integer value.
* src/util/hash.c, src/util/hash.h, src/util/cgroup.c: Replace
  hash code generation with a call to virHashCodeGen()
* src/util/virhashcode.h, src/util/virhashcode.c: Add a new
  virHashCodeGen() API using the Murmurhash3 algorithm.

In preparation for the patch to include Murmurhash3, which
introduces a virhashcode.h and virhashcode.c files, rename
the existing hash.h and hash.c to virhash.h and virhash.c
respectively.

The old virRandom() API was not generating good random numbers.
Replace it with a new API virRandomBits which instead of being
told the upper limit, gets told the number of bits of randomness
required.

* src/util/virrandom.c, src/util/virrandom.h: Add virRandomBits,
  and move virRandomInitialize
* src/util/util.h, src/util/util.c: Delete virRandom and
  virRandomInitialize
* src/libvirt.c, src/security/security_selinux.c,
  src/test/test_driver.c, src/util/iohelper.c: Update for
  changes from virRandom to virRandomBits
* src/storage/storage_backend_iscsi.c: Remove bogus call
  to virRandomInitialize & convert to virRandomBits

There is now a standard QEMU guest agent that can be installed
and given a virtio serial channel

    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/>
      <target type='virtio' name='org.qemu.guest_agent.0'/>
    </channel>

The protocol that runs over the guest agent is JSON based and
very similar to the JSON monitor. We can't use exactly the same
code because there are some odd differences in the way messages
and errors are structured. The qemu_agent.c file is based on
a combination and simplification of qemu_monitor.c and
qemu_monitor_json.c

* src/qemu/qemu_agent.c, src/qemu/qemu_agent.h: Support for
  talking to the agent for shutdown
* src/qemu/qemu_domain.c, src/qemu/qemu_domain.h: Add thread
  helpers for talking to the agent
* src/qemu/qemu_process.c: Connect to agent whenever starting
  a guest
* src/qemu/qemu_monitor_json.c: Make variable static

Preparation for another patch that refactors common patterns
into the new file for fewer lines of code overall.

* src/util/util.h (virTypedParameterArrayClear): Move...
* src/util/virtypedparam.h: ...to new file.
(virTypedParameterArrayValidate, virTypedParameterAssign): New
prototypes.
* src/util/util.c (virTypedParameterArrayClear): Likewise.
* src/util/virtypedparam.c: New file.
* po/POTFILES.in: Mark file for translation.
* src/Makefile.am (UTIL_SOURCES): Build it.
* src/libvirt_private.syms (util.h): Split...
(virtypedparam.h): to new section.
(virkeycode.h): Sort.
* daemon/remote.c: Adjust callers.
* tools/virsh.c: Likewise.

On rawhide, gcc is new enough to output new DWARF information that
pdwtags has not yet learned, but the resulting 'make check' output
was rather confusing:

$ make -C src check
...
  GEN    virkeepaliveprotocol-structs
die__process_function: DW_TAG_INVALID (0x4109) @ <0x58c> not handled!
WARNING: your pdwtags program is too old
WARNING: skipping the virkeepaliveprotocol-structs test
WARNING: install dwarves-1.3 or newer
...
$ pdwtags --version
v1.9

I've filed the pdwtags deficiency as
https://bugzilla.redhat.com/show_bug.cgi?id=772358

* src/Makefile.am (PDWTAGS): Don't leave -t file behind on version
mismatch.  Soften warning message, since 1.9 is newer than 1.3.
Don't leak stderr from broken version.

probes.h can only be generated on Linux, and then only with dtrace
installed.  If it is part of the tarball, then either 'make dist'
will fail if you don't have that setup, or we would have to start
keeping probes.h in libvirt.git.  Since we only need it to be
generated when dtrace is in use, it's better to avoid shipping
it in the first place, and avoid tracking it in git.

Meanwhile, there is a build dependency - since the RPC code is
generated, it can be built early; but when dtrace is enabled, we
must ensure probes.h is built even earlier.  Commit 1afcfbdd tried
to fix this, but did so in a way that added probes.h into the
tarball, and broke VPATH as well.  Commit ecbca767 fixed VPATH,
but didn't fix the more fundamental problem.  This patch solves
the issue by adding a dependency instead.

Tested with 'make dist' in a clean VPATH builds, for both
'./configure --without-dtrace' and './configure --with-dtrace';
all configurations were able to correctly build a tarball, and
the dtrace configuration no longer sticks probes.h in the tarball.

* src/Makefile.am (REMOTE_DRIVER_GENERATED): Don't ship probes.h;
rather, make it a dependency.

To add support for running libvirt on PowerPC, a CPU driver for the
PowerPC platform must be added.
Most generic cpu driver routines such as CPU compare, decode, etc
are based on CPUID comparison and are not relevant for non-x86
platforms.
Here, we introduce stubs for relevant PowerPC routines invoked by libvirt.
Signed-off-by: NPrerna Saxena <prerna@linux.vnet.ibm.com>
Signed-off-by: NAnton Blanchard <anton@au.ibm.com>

The logging APIs need to be able to generate formatted timestamps
using only async signal safe functions. This rules out using
gmtime/localtime/malloc/gettimeday(!) and much more.

Introduce a new internal API which is async signal safe.

  virTimeMillisNowRaw replacement for gettimeofday. Uses clock_gettime
                      where available, otherwise falls back to the unsafe
                      gettimeofday

  virTimeFieldsNowRaw  replacements for gmtime(), convert a timestamp
  virTimeFieldsThenRaw into a broken out set of fields. No localtime()
                       replacement is provided, because converting to
                       local time is not practical with only async signal
                       safe APIs.

  virTimeStringNowRaw  replacements for strftime() which print a timestamp
  virTimeStringThenRaw into a string, using a pre-determined format, with
                       a fixed size buffer (VIR_TIME_STRING_BUFLEN)

For each of these there is also a version without the Raw postfix
which raises a full libvirt error. These versions are not async
signal safe

* src/Makefile.am, src/util/virtime.c, src/util/virtime.h: New files
* src/libvirt_private.syms: New APis
* configure.ac: Check for clock_gettime in -lrt
* tests/virtimetest.c, tests/Makefile.am: Test new APIs

Add the core functions that implement the functionality of the API.
Suspend is done by using an asynchronous mechanism so that we can return
the status to the caller before the host gets suspended. This asynchronous
operation is achieved by suspending the host in a separate thread of
execution. However, returning the status to the caller is only best-effort,
but not guaranteed.

To resume the host, an RTC alarm is set up (based on how long we want to
suspend) before suspending the host. When this alarm fires, the host
gets woken up.

Suspend-to-RAM operation on a host running Linux can take upto more than 20
seconds, depending on the load of the system. (Freezing of tasks, an operation
preceding any suspend operation, is given up after a 20 second timeout).
And Suspend-to-Disk can take even more time, considering the time required
for compaction, creating the memory image and writing it to disk etc.
So, we do not allow the user to specify a suspend duration of less than 60
seconds, to be on the safer side, since we don't want to prematurely declare
failure when we only had to wait for some more time.

This fixes make dist broken by recent keepalive series

These APIs are used by both client and server RPC layer to handle
processing of keepalive messages.

The keepalive program has two procedures: PING, and PONG.
Both are used only in asynchronous messages and the sender doesn't wait
for any reply. However, the party which receives PING messages is
supposed to react by sending PONG message the other party, but no
explicit binding between PING and PONG messages is made. For backward
compatibility neither server nor client are allowed to send keepalive
messages before checking that remote party supports them.

* src/Makefile.am: Remove libvirt_bridge.syms and libvirt_macvtap.syms
  from EXTRA_DIST. Add libvirt_dbus.syms

Mingw32 complains if you request export of a symbol which does
not in fact exist.

* src/libvirt_bridge.syms, src/libvirt_macvtap.syms: Delete
  obsolete files
* src/libvirt_private.syms: Remove virNetServerGetDBusConn
* src/libvirt_dbus.syms: Add virNetServerGetDBusConn

Move the ifaceMacvtapLinkDump and ifaceGetNthParent functions
into virnetdevvportprofile.c since they are specific to that
code. This avoids polluting the headers with the Linux specific
netlink data types

* src/util/interface.c, src/util/interface.h: Move
  ifaceMacvtapLinkDump and ifaceGetNthParent functions and delete
  remaining file
* src/util/virnetdevvportprofile.c: Add ifaceMacvtapLinkDump
  and ifaceGetNthParent functions
* src/network/bridge_driver.c, src/nwfilter/nwfilter_gentech_driver.c,
  src/nwfilter/nwfilter_learnipaddr.c, src/util/virnetdevmacvlan.c:
  Remove include of interface.h

Rename the macvtap.c file to virnetdevmacvlan.c to reflect its
functionality. Move the port profile association code out into
virnetdevvportprofile.c. Make the APIs available unconditionally
to callers

* src/util/macvtap.h: rename to src/util/virnetdevmacvlan.h,
* src/util/macvtap.c: rename to src/util/virnetdevmacvlan.c
* src/util/virnetdevvportprofile.c, src/util/virnetdevvportprofile.h:
  Pull in vport association code
* src/Makefile.am, src/conf/domain_conf.h, src/qemu/qemu_conf.c,
  src/qemu/qemu_conf.h, src/qemu/qemu_driver.c: Update include
  paths & remove conditional compilation

Move the virNetDevSetName and virNetDevSetNamespace APIs out
of LXC's veth.c and into virnetdev.c.

Move the remaining content of the file to src/util/virnetdevveth.c

* src/lxc/veth.c: Rename to src/util/virnetdevveth.c
* src/lxc/veth.h: Rename to src/util/virnetdevveth.h
* src/util/virnetdev.c, src/util/virnetdev.h: Add
  virNetDevSetName and virNetDevSetNamespace
* src/lxc/lxc_container.c, src/lxc/lxc_controller.c,
  src/lxc/lxc_driver.c: Update include paths

The src/util/network.c file is a dumping ground for many different
APIs. Split it up into 5 pieces, along functional lines

 - src/util/virnetdevbandwidth.c: virNetDevBandwidth type & helper APIs
 - src/util/virnetdevvportprofile.c: virNetDevVPortProfile type & helper APIs
 - src/util/virsocketaddr.c: virSocketAddr and APIs
 - src/conf/netdev_bandwidth_conf.c: XML parsing / formatting
   for virNetDevBandwidth
 - src/conf/netdev_vport_profile_conf.c: XML parsing / formatting
   for virNetDevVPortProfile

* src/util/network.c, src/util/network.h: Split into 5 pieces
* src/conf/netdev_bandwidth_conf.c, src/conf/netdev_bandwidth_conf.h,
  src/conf/netdev_vport_profile_conf.c, src/conf/netdev_vport_profile_conf.h,
  src/util/virnetdevbandwidth.c, src/util/virnetdevbandwidth.h,
  src/util/virnetdevvportprofile.c, src/util/virnetdevvportprofile.h,
  src/util/virsocketaddr.c, src/util/virsocketaddr.h: New pieces
* daemon/libvirtd.h, daemon/remote.c, src/conf/domain_conf.c,
  src/conf/domain_conf.h, src/conf/network_conf.c,
  src/conf/network_conf.h, src/conf/nwfilter_conf.h,
  src/esx/esx_util.h, src/network/bridge_driver.c,
  src/qemu/qemu_conf.c, src/rpc/virnetsocket.c,
  src/rpc/virnetsocket.h, src/util/dnsmasq.h, src/util/interface.h,
  src/util/iptables.h, src/util/macvtap.c, src/util/macvtap.h,
  src/util/virnetdev.h, src/util/virnetdevtap.c,
  tools/virsh.c: Update include files

Following the renaming of the bridge management APIs, we can now
split the source file into 3 corresponding pieces

 * src/util/virnetdev.c: APIs for any type of network interface
 * src/util/virnetdevbridge.c: APIs for bridge interfaces
 * src/util/virnetdevtap.c: APIs for TAP interfaces

* src/util/virnetdev.c, src/util/virnetdev.h,
  src/util/virnetdevbridge.c, src/util/virnetdevbridge.h,
  src/util/virnetdevtap.c, src/util/virnetdevtap.h: Copied
  from bridge.{c,h}
* src/util/bridge.c, src/util/bridge.h: Split into 3 pieces
* src/lxc/lxc_driver.c, src/network/bridge_driver.c,
  src/openvz/openvz_driver.c, src/qemu/qemu_command.c,
  src/qemu/qemu_conf.h, src/uml/uml_conf.c, src/uml/uml_conf.h,
  src/uml/uml_driver.c: Update #include directives

While building on FreeBSD (and after fixing a ptsname_r link error),
I got this failure:

./.libs/libvirt_util.a(libvirt_util_la-threads.o)(.text+0x240): In function `virThreadCreate':
util/threads-pthread.c:185: undefined reference to `pthread_create'

It turns out that gnulib used only pthread_join for LIB_PTHREAD,
but on FreeBSD, libc provides that (as a stub function); whereas
the more complex pthread_create really does require -pthread,
which gnulib tracked under [LT]LIBMULTITHREAD.

* configure.ac (LIBS): Check LIBMULTITHREAD alongside LIB_PTHREAD.
* src/Makefile.am (THREAD_LIBS): New variable.
(libvirt_util_la_LIBADD, libvirt_lxc_LDADD): Use it.

The LXC code for mounting container filesystems from block devices
tries all filesystems in /etc/filesystems and possibly those in
/proc/filesystems. The regular mount binary, however, first tries
using libblkid to detect the format. Add support for doing the same
in libvirt, since Fedora's /etc/filesystems is missing many formats,
most notably ext4 which is the default filesystem Fedora uses!

* src/Makefile.am: Link libvirt_lxc to libblkid
* src/lxc/lxc_container.c: Probe filesystem format with libblkid

We already have a /var/lib/libvirt/images for OS install images.
We need a separate /var/lib/libvirt/filesystems for OS install
trees, since SELinux labelling will be different

* libvirt.spec.in: Add /var/lib/libvirt/filesystems
* src/Makefile.am: Create /var/lib/libvirt/filesystems

Deal with the incompatible changes in the VirtualBox 4.1 API.

INetworkAdapter has its different AttachTo* method replaced by
a settable attachmentType property.

The maximum number of network adapters is now requestable per
chipset type.

The OpenMedium method got a bool parameter to request opening
a medium under a new IID.

Add additional fields to let you specify the how to authenticate with a disk.
The secret to use may be referenced by a usage string or a UUID, i.e.:

<auth username='myuser'>
 <secret type='ceph' usage='secretname'/>
</auth>

or

<auth username='myuser'>
 <secret type='ceph' uuid='0a81f5b2-8403-7b23-c8d6-21ccc2f80d6f'/>
</auth>
Signed-off-by: NJosh Durgin <josh.durgin@dreamhost.com>

This change adds some systemtap/dtrace probes to the QEMU monitor
client code. In particular it allows watching of all operations
for a VM

* examples/systemtap/qemu-monitor.stp: Watch all monitor commands
* src/Makefile.am: Passing libdir/bindir/sbindir to dtrace2systemtap.pl
* src/dtrace2systemtap.pl: Accept libdir/bindir/sbindir as args
  and look for '# binary:' comment to mark probes against libvirtd
  vs libvirt.so
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor_json.c,
  src/qemu/qemu_monitor_text.c: Add probes for key functions

When I compile libvirt with gcc-4.6.1 in ubuntu 11.10, got error as below:

  CCLD   libvirtd
/usr/bin/ld: ../src/.libs/libvirt_driver_qemu.a(libvirt_driver_qemu_la-qemu_migration.o): undefined reference to symbol 'gnutls_x509_crt_get_dn@@GNUTLS_1_4'
/usr/bin/ld: note: 'gnutls_x509_crt_get_dn@@GNUTLS_1_4' is defined in DSO /usr/lib/x86_64-linux-gnu/libgnutls.so so try adding it to the linker command line
/usr/lib/x86_64-linux-gnu/libgnutls.so: could not read symbols: Invalid operation
collect2: ld returned 1 exit status
make[3]: *** [libvirtd] Error 1

It can compile with gcc-4.5.2 in ubuntu 11.04, but it can not compile with gcc-4.6.1 in ubuntu 11.10.

I didn't find reason. Does Anyone know the reason or the different between gcc-4.5.2 and gcc-4.6.1?

I still provide a patch for this. Just make it is working now.
Signed-off-by: Nsoulxu <soulxu@soulxu-ThinkPad-T410.(none)>

This adds support for a libvirt client configuration file
either /etc/libvirt/libvirt.conf for privileged clients,
or $HOME/.libvirt/libvirt.conf for unprivileged clients.

It allows one parameter

 uri_aliases = [
   "hail=qemu+ssh://root@hail.cloud.example.com/system",
   "sleet=qemu+ssh://root@sleet.cloud.example.com/system",
 ]

Any call to virConnectOpen with a non-NULL URI will first
attempt to match against the uri_aliases list. An application
can disable this by using VIR_CONNECT_NO_ALIASES

* docs/uri.html.in: Document URI aliases
* include/libvirt/libvirt.h.in: Add VIR_CONNECT_NO_ALIASES
* libvirt.spec.in, mingw32-libvirt.spec.in: Add /etc/libvirt/libvirt.conf
* src/Makefile.am: Install default config file
* src/libvirt.c: Add support for URI aliases
* src/remote/remote_driver.c: Don't try to handle URIs
  with no scheme and which clearly are not paths
* src/util/conf.c: Don't raise error on virConfFree(NULL)
* src/xen/xen_driver.c: Don't raise error on URIs
  with no scheme

probes.h is generated in build directory; setting a dependency on
probes.h from source directory doesn't work well in VPATH builds. Caused
by commit 1afcfbdd

When I run 'make dist', I receive the following error messages:
make[1]: Entering directory `/home/wency/source/libvirt/src'
  GEN    remote/remote_protocol.h
  GEN    remote/remote_protocol.c
  GEN    remote/qemu_protocol.h
  GEN    remote/qemu_protocol.c
  GEN    remote/qemu_client_bodies.h
  CC     libvirt_driver_remote_la-remote_protocol.lo
In file included from ./remote/remote_protocol.h:16,
                 from ./remote/remote_protocol.c:7:
/internal.h:249:23: error: probes.h: No such file or directory
make[1]: *** [libvirt_driver_remote_la-remote_protocol.lo] Error 1
make[1]: Leaving directory `/home/wency/source/libvirt/src'
make: *** [distdir] Error 1

The reason is that we use probes.h before generating it.

Detected by autogen.sh on a cross-mingw build:

Creating library file: .libs/libvirt.dll.a
Cannot export virNetSASLContextCheckIdentity: symbol not defined
Cannot export virNetSASLContextNewServer: symbol not defined
...

* src/libvirt_private.syms (virnetsaslcontext.h): Move symbols...
* src/libvirt_sasl.syms: ...to new file.
* src/Makefile.am (USED_SYM_FILES) [HAVE_SASL]: Use new file.
(EXTRA_DIST): Ship it.

I got these distcheck failures with sanlock enabled:

ERROR: files left in build directory after distclean:
./tools/virt-sanlock-cleanup
./src/locking/qemu-sanlock.conf

* src/Makefile.am (DISTCLEANFILES) [HAVE_SANLOCK]: Clean built
file.
* tools/Makefile.am (DISTCLEANFILES): Likewise.

Otherwise, 'make rpm' fails with:

  GEN    libvirt_qemu.def
make[2]: *** No rule to make target `dtrace2systemtap.pl', needed by `libvirt_probes.stp'.  Stop.

* src/Makefile.am (EXTRA_DIST): Add recent script additions.

The libvirtd daemon had a few crude system tap probes. Some of
these were broken during the RPC rewrite. The new modular RPC
code is structured in a way that allows much more effective
tracing. Instead of trying to hook up the original probes,
define a new set of probes for the RPC and event code.

The master probes file is now src/probes.d.  This contains
probes for virNetServerClientPtr, virNetClientPtr, virSocketPtr
virNetTLSContextPtr and virNetTLSSessionPtr modules. Also add
probes for the poll event loop.

The src/dtrace2systemtap.pl script can convert the probes.d
file into a libvirt_probes.stp file to make use from systemtap
much simpler.

The src/rpc/gensystemtap.pl script can generate a set of
systemtap functions for translating RPC enum values into
printable strings. This works for all RPC header enums (program,
type, status, procedure) and also the authentication enum

The PROBE macro will automatically generate a VIR_DEBUG
statement, so any place with a PROBE can remove any existing
manual DEBUG statements.

* daemon/libvirtd.stp, daemon/probes.d: Remove obsolete probing
* daemon/libvirtd.h: Remove probe macros
* daemon/Makefile.am: Remove all probe buildings/install
* daemon/remote.c: Update authentication probes
* src/dtrace2systemtap.pl, src/rpc/gensystemtap.pl: Scripts
  to generate STP files
* src/internal.h: Add probe macros
* src/probes.d: Master list of probes
* src/rpc/virnetclient.c, src/rpc/virnetserverclient.c,
  src/rpc/virnetsocket.c, src/rpc/virnettlscontext.c,
  src/util/event_poll.c: Insert probe points, removing any
  DEBUG statements that duplicate the info

To avoid static linking libvirtd to the RPC server code, which
then prevents sane introduction of DTrace probes, put it all
in the libvirt.so, and export it

* daemon/Makefile.am: Don't link to RPC libraries
* src/Makefile.am: Link all RPC libraries to libvirt.so
* src/libvirt_private.syms: Export all RPC functions

I am getting this failure with 'make distcheck':

  GEN    ../../src/remote_protocol-structs
/bin/sh: ../../src/remote_protocol-structs-t: Permission denied
make[4]: *** [../../src/remote_protocol-structs] Error 1

since it attempts a sub-run of a VPATH 'make check' where $(srcdir)
is intentionally read-only.  I'm not sure which commit introduced
the problem, although I suspect it was around 62dee6fa when I
refactored protocol struct checking to be more powerful.

$(@F) is required by POSIX, and although it is not yet portable
to all make implementations, we already require GNU make.

* src/Makefile.am (PDWTAGS): Generate temp file into current
directory, since $(srcdir) is read-only during distcheck.

Inexplicably the sanlock code all got placed under the GPLv2-only,
so libvirt's use of sanlock introduces a license incompatibility.
The sanlock developers have now rearranged the code such that there
is a 'sanlock_client.so' which is LGPLv2+ while their daemon remains
GPLv2-only. To use the new client library we need to call the new
sanlock_init and sanlock_align APIs instead of sanlock_direct_init
and sanlock_direct_align. These APIs calls are now routed via the
sanlock daemon, instead of doing direct I/O calls to disk.

For all this we require sanlock >= 1.8

* configure.ac: Check for sanlock_client.so instead of sanlock.so
  and fix various comments
* libvirt.spec.in: Mandate sanlock >= 1.8
* src/Makefile.am: Link to -lsanlock_client
* src/locking/lock_driver_sanlock.c: Use sanlock_init and
  sanlock_align

When libvirt calls virInitialize it creates a thread local
for the virErrorPtr storage, and registers a callback to
cleanup memory when a thread exits. When libvirt is dlclose()d
or otherwise made non-resident, the callback function is
removed from memory, but the thread local may still exist
and if a thread later exists, it will invoke the callback
and SEGV. There may also be other thread locals with callbacks
pointing to libvirt code, so it is in general never safe to
unload libvirt.so from memory once initialized.

To allow dlclose() to succeed, but keep libvirt.so resident
in memory, link with '-z nodelete'. This issue was first
found with the libvirt CIM provider, but can potentially
hit many of the dynamic language bindings which all ultimately
involve dlopen() in some way, either on libvirt.so itself,
or on the glue code for the binding which in turns links
to libvirt

* configure.ac, src/Makefile.am: Ensure libvirt.so is linked
  with -z nodelete
* cfg.mk, .gitignore, tests/Makefile.am, tests/shunloadhelper.c,
  tests/shunloadtest.c: A test case to unload libvirt while
  a thread is still running.

This patch adds the ability to make the filesystem for a filesystem
pool during a pool build.

The patch adds two new flags, no overwrite and overwrite, to control
when mkfs gets executed.  By default, the patch preserves the
current behavior, i.e., if no flags are specified, pool build on a
filesystem pool only makes the directory on which the filesystem
will be mounted.

If the no overwrite flag is specified, the target device is checked
to determine if a filesystem of the type specified in the pool is
present.  If a filesystem of that type is already present, mkfs is
not executed and the build call returns an error.  Otherwise, mkfs
is executed and any data present on the device is overwritten.

If the overwrite flag is specified, mkfs is always executed, and any
existing data on the target device is overwritten unconditionally.