Hi Alexei,
On Tue, Jan 27, 2015 at 08:06:06PM -0800, Alexei Starovoitov wrote:
> User interface:
> fd = open("/sys/kernel/debug/tracing/__event__/filter")
>
> write(fd, "bpf_123")
>
> where 123 is process local FD associated with eBPF program previously loaded.
> __event__ is static tracepoint event or syscall.
> (kprobe support is in next patch)
> Once program is successfully attached to tracepoint event, the tracepoint
> will be auto-enabled
>
> close(fd)
> auto-disables tracepoint event and detaches eBPF program from it
>
> eBPF programs can call in-kernel helper functions to:
> - lookup/update/delete elements in maps
> - memcmp
> - fetch_ptr/u64/u32/u16/u8 values from unsafe address via probe_kernel_read(),
> so that eBPF program can walk any kernel data structures
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> ---
[SNIP]
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index b03a0ea77b99..70482817231a 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -1084,6 +1084,26 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
> return r;
> }
>
> +static int event_filter_release(struct inode *inode, struct file *filp)
> +{
> + struct ftrace_event_file *file;
> + char buf[2] = "0";
> +
> + mutex_lock(&event_mutex);
> + file = event_file_data(filp);
> + if (file) {
> + if (file->flags & TRACE_EVENT_FL_BPF) {
> + /* auto-disable the filter */
> + ftrace_event_enable_disable(file, 0);
Hmm.. what if user already enabled an event, attached a bpf filter and
then detached the filter - I'm not sure we can always auto-disable
it..
> +
> + /* if BPF filter was used, clear it on fd close */
> + apply_event_filter(file, buf);
> + }
> + }
> + mutex_unlock(&event_mutex);
> + return 0;
> +}
> +
> static ssize_t
> event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
> loff_t *ppos)
> @@ -1107,8 +1127,18 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
>
> mutex_lock(&event_mutex);
> file = event_file_data(filp);
> - if (file)
> + if (file) {
> + /*
> + * note to user space tools:
> + * write() into debugfs/tracing/events/xxx/filter file
> + * must be done with the same privilege level as open()
> + */
> err = apply_event_filter(file, buf);
> + if (!err && file->flags & TRACE_EVENT_FL_BPF)
> + /* once filter is applied, auto-enable it */
> + ftrace_event_enable_disable(file, 1);
> + }
> +
> mutex_unlock(&event_mutex);
>
> free_page((unsigned long) buf);
> @@ -1363,6 +1393,7 @@ static const struct file_operations ftrace_event_filter_fops = {
> .open = tracing_open_generic,
> .read = event_filter_read,
> .write = event_filter_write,
> + .release = event_filter_release,
> .llseek = default_llseek,
> };
>
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index ced69da0ff55..e0303b3cc9fb 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -23,6 +23,9 @@
> #include <linux/mutex.h>
> #include <linux/perf_event.h>
> #include <linux/slab.h>
> +#include <linux/bpf.h>
> +#include <trace/bpf_trace.h>
> +#include <linux/filter.h>
>
> #include "trace.h"
> #include "trace_output.h"
> @@ -541,6 +544,21 @@ static int filter_match_preds_cb(enum move_type move, struct filter_pred *pred,
> return WALK_PRED_DEFAULT;
> }
>
> +unsigned int trace_filter_call_bpf(struct event_filter *filter, void *ctx)
> +{
> + unsigned int ret;
> +
> + if (in_nmi()) /* not supported yet */
> + return 0;
But doesn't this mean to auto-disable all attached events during NMI
as returning 0 will prevent the event going to ring buffer?
I think it'd be better to keep an attached event in a soft-disabled
state like event trigger and give control of enabling to users..
Thanks,
Namhyung
> +
> + rcu_read_lock();
> + ret = BPF_PROG_RUN(filter->prog, ctx);
> + rcu_read_unlock();
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(trace_filter_call_bpf);
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