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doc: bpf_get_current_task helper #1547

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Jan 30, 2018
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doc: bpf_get_current_task helper #1547

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28 changes: 26 additions & 2 deletions docs/reference_guide.md
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,8 @@ This guide is incomplete. If something feels missing, check the bcc and kernel s
- [4. bpf_get_current_pid_tgid()](#4-bpf_get_current_pid_tgid)
- [5. bpf_get_current_uid_gid()](#5-bpf_get_current_uid_gid)
- [6. bpf_get_current_comm()](#6-bpf_get_current_comm)
- [7. bpf_log2l()](#7-bpflog2l)
- [7. bpf_get_current_task()](#7-bpf_get_current_task)
- [8. bpf_log2l()](#8-bpflog2l)
- [Debugging](#debugging)
- [1. bpf_override_return()](#1-bpf_override_return)
- [Output](#output)
Expand Down Expand Up @@ -316,7 +317,30 @@ Examples in situ:
[search /examples](https://github.com/iovisor/bcc/search?q=bpf_get_current_comm+path%3Aexamples&type=Code),
[search /tools](https://github.com/iovisor/bcc/search?q=bpf_get_current_comm+path%3Atools&type=Code)

### 7. bpf_log2l()
### 7. bpf_get_current_task()

Syntax: ```bpf_get_current_task()```

Return: current task as a pointer to struct task_struct.

Returns a pointer to the current task's task_struct object. This helper can be used to compute the on-CPU time for a process, identify kernel threads, get the current CPU's run queue, or retrieve many other pieces of information.

With Linux 4.13, due to issues with field randomization, you may need two #define directives before the includes:
```C
#define randomized_struct_fields_start struct {
#define randomized_struct_fields_end };
#include <linux/sched.h>

int do_trace(void *ctx) {
struct task_struct *t = (struct task_struct *)bpf_get_current_task();
[...]
```

Examples in situ:
[search /examples](https://github.com/iovisor/bcc/search?q=bpf_get_current_task+path%3Aexamples&type=Code),
[search /tools](https://github.com/iovisor/bcc/search?q=bpf_get_current_task+path%3Atools&type=Code)

### 8. bpf_log2l()

Syntax: ```unsigned int bpf_log2l(unsigned long v)```

Expand Down