66 lines
2 KiB
C++
66 lines
2 KiB
C++
#include <cstdint>
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#include <sys/mman.h>
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#include <sys/syscall.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <stdexcept>
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#include <cstring>
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#include <utility>
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namespace lrbm {
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static int create_memfd(const char* name) {
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int fd = syscall(SYS_memfd_create, name, 0);
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if (fd == -1) throw std::runtime_error("memfd_create failed");
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return fd;
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}
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std::pair<void*, size_t> create_linear_ring(size_t size) {
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const size_t page = sysconf(_SC_PAGESIZE);
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size_t aligned = (size + page - 1) & ~(page - 1);
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// Create RAM-backed file descriptor
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int fd = create_memfd("linear_ring");
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if (ftruncate(fd, aligned) != 0) throw std::runtime_error("ftruncate failed");
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// Reserve 2× VA space
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uint8_t* base = (uint8_t*) mmap(nullptr, aligned * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (base == MAP_FAILED) throw std::runtime_error("mmap reserve failed");
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// First mapping
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void* p1 = mmap(base, aligned, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED, fd, 0);
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if (p1 != base) throw std::runtime_error("first mmap failed");
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// Mirror mapping
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void* p2 = mmap(base + aligned, aligned, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED, fd, 0);
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if (p2 != base + aligned) throw std::runtime_error("mirror mmap failed");
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close(fd);
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return { base, aligned }; // linear region [buf][buf]
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}
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void destroy_linear_ring(void* base, size_t size) { munmap(base, size); }
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// void test() {
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// const size_t RING_SIZE = 4096;
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// uint8_t* ring = (uint8_t*) create_linear_ring(RING_SIZE);
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// printf("Linear ring created at %p (size = %zu)\n", ring, RING_SIZE);
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// const char* msg = "HELLO_LINEAR_RING";
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// size_t msg_len = strlen(msg);
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// size_t head = RING_SIZE - 4; // force boundary crossing
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// std::memcpy(ring + head, msg, msg_len);
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// char out[64];
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// std::memcpy(out, ring + head, msg_len);
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// out[msg_len] = 0;
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// printf("Expected: %s\n", msg);
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// printf("Readback: %s\n", out);
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// if (std::strcmp(msg, out) == 0) printf("SUCCESS: Linear-address ring works!\n");
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// else printf("FAILURE: Ring broken!\n");
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// }
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}
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