On 6/12/15 3:08 PM, Andy Lutomirski wrote:
On Fri, Jun 12, 2015 at 2:40 PM, Alexei Starovoitov <a...@plumgrid.com> wrote:
eBPF programs attached to kprobes need to filter based on
current->pid, uid and other fields, so introduce helper functions:
u64 bpf_get_current_pid_tgid(void)
Return: current->tgid << 32 | current->pid
u64 bpf_get_current_uid_gid(void)
Return: current_gid << 32 | current_uid
How does this work wrt namespaces,
from_kuid(current_user_ns(), uid)
> and why the weird packing?
to minimize number of calls.
We've considered several alternatives.
1. 5 different helpers
Cons: every call adds performance overhead
2a: single helper that populates 'struct bpf_task_info'
and uses 'flags' with bit per field.
+struct bpf_task_info {
+ __u32 pid;
+ __u32 tgid;
+ __u32 uid;
+ __u32 gid;
+ char comm[16];
+};
bpf_get_current_task_info(task_info, size, flags)
bit 0 - fill in pid
bit 1 - fill in tgid
Pros: single helper
Cons: ugly to use and a lot of compares in the helper
itself (two compares for each field)
2b. single helper that populates 'struct bpf_task_info'
and uses 'size' to tell how many fields to fill in.
bpf_get_current_task_info(task_info, size);
+ if (size >= offsetof(struct bpf_task_info, pid) + sizeof(info->pid))
+ info->pid = task->pid;
+ if (size >= offsetof(struct bpf_task_info, tgid) +
sizeof(info->tgid))
+ info->tgid = task->tgid;
Pros: single call (with single compare per field).
Cons: still hard to use when only uid is needed.
These three helpers looked as the best balance between
performance and usability.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
