perfcounters: provide expansion room in the ABI

Impact: ABI change

This expands several fields in the perf_counter_hw_event struct and adds
a "flags" argument to the perf_counter_open system call, in order that
features can be added in future without ABI changes.

In particular the record_type field is expanded to 64 bits, and the
space for flag bits has been expanded from 32 to 64 bits.

This also adds some new fields:

* read_format (64 bits) is intended to provide a way to specify what
  userspace wants to get back when it does a read() on a simple
  (non-interrupting) counter;

* exclude_idle (1 bit) provides a way for userspace to ask that events
  that occur when the cpu is idle be excluded;

* extra_config_len will provide a way for userspace to supply an
  arbitrary amount of extra machine-specific PMU configuration data
  immediately following the perf_counter_hw_event struct, to allow
  sophisticated users to program things such as instruction matching
  CAMs and address range registers;

* __reserved_3 and __reserved_4 provide space for future expansion.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 16b14ba99d34..b2e838959f3e 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1683,16 +1683,16 @@ perf_counter_alloc(struct perf_counter_hw_event *hw_event,
 }
 
 /**
- * sys_perf_task_open - open a performance counter, associate it to a task/cpu
+ * sys_perf_counter_open - open a performance counter, associate it to a task/cpu
  *
  * @hw_event_uptr:      event type attributes for monitoring/sampling
  * @pid:                target pid
  * @cpu:                target cpu
  * @group_fd:           group leader counter fd
  */
-SYSCALL_DEFINE4(perf_counter_open,
+SYSCALL_DEFINE5(perf_counter_open,
                 const struct perf_counter_hw_event __user *, hw_event_uptr,
-                pid_t, pid, int, cpu, int, group_fd)
+                pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)
 {
         struct perf_counter *counter, *group_leader;
         struct perf_counter_hw_event hw_event;
@@ -1703,6 +1703,10 @@ SYSCALL_DEFINE4(perf_counter_open,
         int fput_needed2 = 0;
         int ret;
 
+        /* for future expandability... */
+        if (flags)
+                return -EINVAL;
+
         if (copy_from_user(&hw_event, hw_event_uptr, sizeof(hw_event)) != 0)
                 return -EFAULT;