Re: [PATCH RFC net-next 03/14] bpf: introduce syscall(BPF, ...) and BPF maps

[Alexei Starovoitov]

On Sat, Jun 28, 2014 at 6:52 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Sat, Jun 28, 2014 at 1:49 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
>>
>> Sorry I don't like 'fd' direction at all.
>> 1. it will make the whole thing very socket specific and 'net' dependent.
>> but the goal here is to be able to use eBPF for tracing in embedded
>> setups. So it's gotta be net independent.
>> 2. sockets are already overloaded with all sorts of stuff. Adding more
>> types of sockets will complicate it a lot.
>> 3. and most important. read/write operations on sockets are not
>> done every nanosecond, whereas lookup operations on bpf maps
>> are done every dozen instructions, so we cannot have any overhead
>> when accessing maps.
>> In other words the verifier is done as static analyzer. I moved all
>> the complexity to verify time, so at run-time the programs are as
>> fast as possible. I'm strongly against run-time checks in critical path,
>> since they kill performance and make the whole approach a lot less usable.
>
> I may have described my suggestion poorly.  I'm suggesting that all of
> these global ids be replaced *for userspace's benefit* with fds.  That
> is, a map would have an associated struct inode, and, when you load an
> eBPF program, you'd pass fds into the kernel instead of global ids.
> The kernel would still compile the eBPF program to use the global ids,
> though.

Hmm. If I understood you correctly, you're suggesting to do it similar
to ipc/mqueue, shmem, sockets do. By registering and mounting
a file system and providing all superblock and inode hooksâ and
probably have its own namespace typeâ hmmâ may be. That's
quite a bit of work to put lightly. As I said in the other email the first
step is root only and all these complexity just not worth doing
at this stage.
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