It turns out it is also useful to be able to perform other operations
on a file created while running as a different uid (eg, write things
to that file), and possibly to do this to a file that already
exists. This patch adds an optional hook function to the renamed (for
more accuracy of purpose) virFileOperation; the hook will be called
after the file has been opened (possibly created) and gid/mode
checked/set, before closing it.

As with the other operations on the file, if the VIR_FILE_OP_AS_UID
flag is set, this hook function will be called in the context of a
child process forked from the process that called virFileOperation.
The implication here is that, while all data in memory is available to
this hook function, any modification to that data will not be seen by
the caller - the only indication in memory of what happened in the
hook will be the return value (which the hook should set to 0 on
success, or one of the standard errno values on failure).

Another piece of making the function more flexible was to add an
"openflags" argument. This arg should contain exactly the flags to be
passed to open(2), eg O_RDWR | O_EXCL, etc.

In the process of adding the hook to virFileOperation, I also realized
that the bits to fix up file owner/group/mode settings after creation
were being done in the parent process, which could fail, so I moved
them to the child process where they should be.

* src/util/util.[ch]: rename and rework virFileCreate-->virFileOperation,
  and redo flags in virDirCreate
* storage/storage_backend.c, storage/storage_backend_fs.c: update the
  calls to virFileOperation/virDirCreate to reflect changes in the API,
  but don't yet take advantage of the hook.

If the hostname as returned by "gethostname" resolves
to "localhost" (as it does with the broken Fedora-12
installer), then live migration will fail because the
source will try to migrate to itself.  Detect this
situation up-front and abort the live migration before
we do any real work.

* src/util/util.h src/util/util.c: add a new virGetHostnameLocalhost
  with an optional localhost check, and rewire virGetHostname() to use
  it
* src/libvirt_private.syms: expose the new function
* src/qemu/qemu_driver.c: use it in qemudDomainMigratePrepare2()

* src/util/pci.c: update 2 message on pciRead errors

* src/util/buf.c (virBufferStrcat): Do not skip va_end due to
an early return.

* src/util/qparams.c (new_qparam_set, append_qparams): Do not skip
va_end due to an early return.

This patch sets or unsets the IFF_VNET_HDR flag depending on what device
is used in the VM. The manipulation of the flag is done in the open
function and is only fatal if the IFF_VNET_HDR flag could not be cleared
although it has to be (or if an ioctl generally fails). In that case the
macvtap tap is closed again and the macvtap interface torn.

* src/qemu/qemu_conf.c src/qemu/qemu_conf.h: pass qemuCmdFlags to
  qemudPhysIfaceConnect()
* src/util/macvtap.c src/util/macvtap.h: add vnet_hdr boolean to
  openMacvtapTap(), and private function configMacvtapTap()
* src/qemu/qemu_driver.c: add extra qemuCmdFlags when calling
  qemudPhysIfaceConnect()

For __virExec() this is a semantic NOP except for when fork()
fails. __virExec() would previously forget to restore the signal mask
in this case; virFork() corrects this behavior.

virFileCreate() and virDirCreate() gain the code to reset the logging
and properly deal with the signal handling race condition.

This also removes a log message that had a typo ("cannot fork o create
file '%s'") - this error is now logged in a more generic manner in
virFork() (more generic, but really just as informative, since the
fact that it's forking to create a file is immaterial to the fact that
it simply can't fork)

* src/util/util.c: use the generic virFork() in the 3 functions

virFork() contains bookkeeping that must be done any time a process
forks. Currently this includes:

1) Call virLogLock() prior to fork() and virLogUnlock() just after,
   to avoid a deadlock if some other thread happens to hold that lock
   during the fork.

2) Reset the logging hooks and send all child process log messages to
   stderr.

3) Block all signals prior to fork(), then either a) reset the signal
   mask for the parent process, or b) clear the signal mask for the
   child process.

Note that the signal mask handling in __virExec erroneously fails to
restore the signal mask when fork() fails. virFork() fixes this
problem.

Other than this, it attempts to behave as closely to fork() as
possible (including preserving errno for the caller), with a couple
exceptions:

1) The return value is 0 (success) or -1 (failure), while the pid is
   returned via the pid_t* argument. Like fork(), if pid < 0 there is
   no child process, otherwise both the child and the parent will
   return to the caller, and both should look at the return value,
   which will indicate if some of the extra processing outlined above
   encountered an error.

2) If virFork() returns with pid < 0 or with a return value < 0
   indicating an error condition, the error has already been
   reported. You can log an additional message if you like, but it
   isn't necessary, and may be awkwardly extraneous.

Note that virFork()'s child process will *never* call _exit() - if a
child process is created, it will return to the caller.

* util.c util.h: add virFork() function, based on what is currently
                 done in __virExec().

virGetLastError returns NULL if no error has been set, not on
allocation error like virSetError assumed. Use virLastErrorObject
instead. This fixes virSetError when no error is currently stored.

Rework and simplification of teardown of the macvtap device.

Basically all devices with the same MAC address and link device are kept
alive and not attempted to be torn down. If a macvtap device linked to a
physical interface with a certain MAC address 'M' is to be created it
will automatically fail if the interface is 'up'ed and another macvtap
with the same properties (MAC addr 'M', link dev) happens to be 'up'.
This will prevent the VM from starting or the device from being attached
to a running VM. Stale interfaces are assumed to be there for some
reason and not stem from libvirt.

In the VM shutdown path, it's assuming that an interface name is always
available so that if the device type is DIRECT it can be torn down
using its name.

* src/util/macvtap.h src/libvirt_macvtap.syms: change of deleting routine
* src/util/macvtap.c: cleanups and change of deleting routine
* src/qemu/qemu_driver.c: change cleanup on shutdown
* src/qemu/qemu_conf.c: don't delete Macvtap in qemudPhysIfaceConnect()

This part adds the helper code to setup and tear down macvtap devices
using direct communication with the device driver via netlink sockets.
The rather short messages received from the netlink layer are now
written into a dynamically allocated buffer

* src/util/macvtap.h src/util/macvtap.c: provides the new module
* po/POTFILES.in: the module contains translated strings

This part adds support to domain_conf.{c|h} for parsing the new
interface XML of type 'direct'. The parsed mode is now stored as
an int.
* src/conf/domain_conf.c src/conf/domain_conf.h: extend parsing code
* src/util/macvtap.h: empty header to not break compilation

This patch adds build support for libvirt checking for certain contents
of /usr/include/linux/if_link.h to see whether macvtap support is
compilable on that system. One can disable macvtap support in libvirt
via --without-macvtap passed to configure.
* configure.ac src/Makefile.am: new build support
* src/libvirt_macvtap.syms: list of exported symbols
* src/util/macvtap.c: empty module to not break compilation

* src/util/hostusb.c: The device path for a USB device wants the
  bus/device IDs in decimal not octal

All callers now pass a NULL virConnectPtr into the USB/PCi device
iterator functions. Therefore the virConnectPtr arg can now be
removed from these functions

* src/util/hostusb.h, src/util/hostusb.c: Remove virConnectPtr
  from usbDeviceFileIterate
* src/util/pci.c, src/util/pci.h: Remove virConnectPtr arg from
  pciDeviceFileIterate
* src/qemu/qemu_security_dac.c, src/security/security_selinux.c: Update
  to drop redundant virConnectPtr arg

* src/util/util.h (virAsprintf): Remove ATTRIBUTE_RETURN_CHECK, since
it is perfectly fine to ignore the return value, now that the pointer
is guaranteed to be set to NULL upon failure.
* src/util/storage_file.c (absolutePathFromBaseFile): Remove now-
unnecessary use of ignore_value.

* src/util/storage_file.c (absolutePathFromBaseFile): While this use
of virAsprintf is slightly cleaner than using stpncpy(stpcpy(...,
it does impose an artificial limitation on the length of the base_file
name.  Rather than asserting that it does not exceed INT_MAX, return
NULL when it does.

It was used for error reporting only.

It was used for error reporting only.

It was used for error reporting only.

It was used for error reporting only.

It was used for error reporting only.

It was used for error reporting only.

When configured with --enable-gcc-warnings, it didn't even compile.
* src/util/storage_file.c: Include <assert.h>.
(absolutePathFromBaseFile): Assert that converting size_t to int is valid.
Reverse length/string args to match "%.*s".
Explicitly ignore the return value of virAsprintf.

* src/util/storage_file.c: Include "dirname.h".
(absolutePathFromBaseFile): Rewrite not to leak, and to require
fewer allocations.
* bootstrap (modules): Add dirname-lgpl.
* .gnulib: Update submodule to the latest.

* src/util/util.c (virExecWithHook): Free argv_str string before
returning upon failure to allocate space for environment.

* src/util/cgroup.c (virCgroupDetectPlacement): Close the mapping
FILE* also upon error.

* src/util/cgroup.c (virCgroupCpuSetInherit) [HAVE_MNTENT_H]:
Don't leak CPU-set inheritance value strings.

Similar fix as previous one but for fork() usage when creating
a file or directory

* src/util/util.c: virLogLock() and virLogUnlock() around fork()
  in virFileCreate() and virDirCreateSimple()

Ad pointed out by Dan Berrange:
So if some thread in libvirtd is currently executing a logging call,
while another thread calls virExec(), that other thread no longer
exists in the child, but its lock is never released. So when the
child then does virLogReset() it deadlocks.

The only way I see to address this, is for the parent process to call
virLogLock(), immediately before fork(), and then virLogUnlock()
afterwards in both parent & child. This will ensure that no other
thread
can be holding the lock across fork().

* src/util/logging.[ch] src/libvirt_private.syms: export virLogLock() and
  virLogUnlock()
* src/util/util.c: lock just before forking and unlock just after - in
  both parent and child.

* src/util/util.c (virGetUserID, virGetGroupID): In the unlikely event
that sysconf(_SC_GETPW_R_SIZE_MAX) fails, don't use -1 as the size in
the subsequent allocation.

* src/util/json.c (virJSONValueFree): Free the "value" pointer, too.

Signed-off-by: NChris Lalancette <clalance@redhat.com>

On RHEL-5 the qemu-kvm binary is located in /usr/libexec.
To reduce confusion for people trying to run upstream libvirt
on RHEL-5 machines, make the qemu driver look in /usr/libexec
for the qemu-kvm binary.

To make this work, I modified virFindFileInPath to handle an
absolute path correctly.  I also ran into an issue where
NULL was sometimes being passed for the file parameter
to virFindFileInPath; it didn't crash prior to this patch
since it was building paths like /usr/bin/(null).  This
is non-standard behavior, though, so I added a NULL
check at the beginning.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

* src/util/util.c (virGetUserEnt): In the unlikely event that
sysconf(_SC_GETPW_R_SIZE_MAX) fails, don't use -1 as the size in
the subsequent allocation.

* src/util/pci.c (pciDeviceDownstreamLacksACS): Fix a typo
that rendered a subexpression always false.