Fixes to the xenoprofile Linux driver.

Fixes to the xenoprofile Linux driver.

The active_domains code has race conditions:

* oprofile_set_active() calls set_active() method without holding
  start_sem.  This is clearly wrong, as xenoprof_set_active() makes
  several hypercalls.  oprofile_start(), for instance, could run in
  the middle of xenoprof_set_active().

* adomain_write(), adomain_read() and xenoprof_set_active() access
  global active_domains[] and adomains without synchronization.  I
  went for a simple, obvious fix and created another mutex.  Instead,
  one could move the shared data into oprof.c and protect it with
  start_sem, but that's more invasive.

Also clean up the code dealing with /dev/oprofile/active_domains:

* Use parameters instead of global variables to pass domain ids
  around.  Give those globals internal linkage.

* Allocate buffers dynamically to conserve stack space.

* Treat writes with size zero exactly like a write containing no
  domain id.  Before, zero-sized write was ignored, which is not the
  same.

* Parse domain ids as unsigned numbers.  Before, the first one was
  parsed as signed number.

  Because ispunct()-punctuation is ignored between domain ids, signs
  are still silently ignored except for the first number.  Hmm.

* Make parser accept whitespace as domain separator, because that's
  what you get when reading the file.

* EINVAL on domain ids overflowing domid_t.  Before, they were
  silently truncated.

* EINVAL on too many domain ids.  Before, the excess ones were
  silently ignored.

* Reset active domains on failure halfway through setting them.

* Fix potential buffer overflow in adomain_read().  Couldn't really
  happen because buffer was sufficient for current value of
  MAX_OPROF_DOMAINS.

Signed-off-by: Markus Armbruster <armbru@redhat.com>