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Can AF_XDP use in kernel? #350

Open e493956170 opened 1 year ago

e493956170 commented 1 year ago

Can i use sock_create_kern to create AF_XDP in kernel?

tohojo commented 1 year ago

e493956170 @.***> writes:

Can i use sock_create_kern to create AF_XDP in kernel?

Erm, no? Whaddyamean, "in kernel"?

e493956170 commented 1 year ago

emm... I mean I want to create an AF_XDP socket in a kernel thread. Is this usage feasiable?

tohojo commented 1 year ago

azureglow @.***> writes:

emm... I mean I want to create an AF_XDP socket in a kernel thread. Is this usage feasiable?

Don't believe that's possible, no. What's the use case, exactly?

e493956170 commented 1 year ago

azureglow @.***> writes: emm... I mean I want to create an AF_XDP socket in a kernel thread. Is this usage feasiable? Don't believe that's possible, no. What's the use case, exactly?

Some ideas for bypassing protocol stack

tohojo commented 1 year ago

azureglow @.***> writes:

Some ideas for bypassing protocol stack

Well, if you're inside the kernel AF_XDP doesn't really make sense; that is there specifically for getting packets to userspace without the syscall overhead. An in-kernel consumer can just operate on xdp_frames directly.

Having such an in-kernel consumer of XDP frames may be interesting, but you're going to have to be a bit more specific to know for sure... :)

e493956170 commented 1 year ago

azureglow @.***> writes: Some ideas for bypassing protocol stack Well, if you're inside the kernel AF_XDP doesn't really make sense; that is there specifically for getting packets to userspace without the syscall overhead. An in-kernel consumer can just operate on xdp_frames directly. Having such an in-kernel consumer of XDP frames may be interesting, but you're going to have to be a bit more specific to know for sure... :)

In fact, I am new to kernel. I want to how to operate xdp_frames directly? After serveral tries, PF_XDP is ok to init in kernel with sock_create_kern(), but the operation of UMEM_REG will always failed due to bad address. I have to know more about this area, thanks.

tohojo commented 1 year ago

azureglow @.***> writes:

azureglow @.***> writes: Some ideas for bypassing protocol stack Well, if you're inside the kernel AF_XDP doesn't really make sense; that is there specifically for getting packets to userspace without the syscall overhead. An in-kernel consumer can just operate on xdp_frames directly. Having such an in-kernel consumer of XDP frames may be interesting, but you're going to have to be a bit more specific to know for sure... :)

In fact, I am new to kernel. I want to how to operate xdp_frames directly?

Well, there's no existing interface for doing this; you'd probably need to create a new map type and use that as a target for bpf_redirect_map(). You can look at the existing devmap or cpumap code for an example.

After serveral tries, PF_XDP is ok to init in kernel with sock_create_kern(), but the operation of UMEM_REG will always failed due to bad address. I have to know more about this area, thanks.

Well, as the name implies UMEM is userspace memory, so the kernel won't let you register kernel memory. And, again, you really don't need to from an in-kernel consumer.