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The ring mapped provided buffer rings rely on the application allocating the memory for the ring, and then the kernel will map it. This generally works fine, but runs into issues on some architectures where we need to be able to ensure that the kernel and application virtual address for the ring play nicely together. This at least impacts architectures that set SHM_COLOUR, but potentially also anyone setting SHMLBA. To use this variant of ring provided buffers, the application need not allocate any memory for the ring. Instead the kernel will do so, and the allocation must subsequently call mmap(2) on the ring with the offset set to: IORING_OFF_PBUF_RING | (bgid << IORING_OFF_PBUF_SHIFT) to get a virtual address for the buffer ring. Normally the application would allocate a suitable piece of memory (and correctly aligned) and simply pass that in via io_uring_buf_reg.ring_addr and the kernel would map it. Outside of the setup differences, the kernel allocate + user mapped provided buffer ring works exactly the same. Acked-by: Helge Deller <deller@gmx.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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