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    Subject[RFC PATCH] 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>
    ---
    This should provide plenty of room for future expansion, in fact maybe
    it's a little over the top.

    Ingo, if this looks OK, you can pull it from the rfc branch of my
    perfcounters.git tree at:

    git://git.kernel.org/pub/scm/linux/kernel/git/paulus/perfcounters.git rfc

    include/linux/perf_counter.h | 12 +++++++++---
    include/linux/syscalls.h | 2 +-
    kernel/perf_counter.c | 10 +++++++---
    3 files changed, 17 insertions(+), 7 deletions(-)

    diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
    index 186efaf..c42455a 100644
    --- a/include/linux/perf_counter.h
    +++ b/include/linux/perf_counter.h
    @@ -69,9 +69,10 @@ struct perf_counter_hw_event {
    __s64 type;

    __u64 irq_period;
    - __u32 record_type;
    + __u64 record_type;
    + __u64 read_format;

    - __u32 disabled : 1, /* off by default */
    + __u64 disabled : 1, /* off by default */
    nmi : 1, /* NMI sampling */
    raw : 1, /* raw event type */
    inherit : 1, /* children inherit it */
    @@ -80,10 +81,15 @@ struct perf_counter_hw_event {
    exclude_user : 1, /* don't count user */
    exclude_kernel : 1, /* ditto kernel */
    exclude_hv : 1, /* ditto hypervisor */
    + exclude_idle : 1, /* don't count when idle */

    - __reserved_1 : 23;
    + __reserved_1 : 55;
    +
    + __u32 extra_config_len;
    + __u32 __reserved_4;

    __u64 __reserved_2;
    + __u64 __reserved_3;
    };

    /*
    diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
    index 28ef2be..ab1d772 100644
    --- a/include/linux/syscalls.h
    +++ b/include/linux/syscalls.h
    @@ -698,5 +698,5 @@ int kernel_execve(const char *filename, char *const argv[], char *const envp[]);

    asmlinkage long sys_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);
    #endif
    diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
    index 16b14ba..b2e8389 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;

    --
    1.5.6.3


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