// ss_os_acquire_box.c - SuperSlab OS Memory Acquisition Box Implementation
#include "ss_os_acquire_box.h"
#include "../hakmem_build_flags.h"
#include <sys/mman.h>
#include <sys/resource.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// Global counters for debugging (non-static for external access)
_Atomic uint64_t g_ss_mmap_count = 0;
_Atomic uint64_t g_final_fallback_mmap_count = 0;

// ============================================================================
// OOM Diagnostics
// ============================================================================

static void log_superslab_oom_once(size_t ss_size, size_t alloc_size, int err) {
    static int logged = 0;
    if (logged) return;
    logged = 1;

    // CRITICAL FIX: Increment lock depth FIRST before any LIBC calls
    // fopen/fclose/getrlimit/fprintf all may call malloc internally
    // Must bypass HAKMEM wrapper to avoid header mismatch crash
    extern __thread int g_hakmem_lock_depth;
    g_hakmem_lock_depth++;  // Force wrapper to use __libc_malloc

    struct rlimit rl = {0};
    if (getrlimit(RLIMIT_AS, &rl) != 0) {
        rl.rlim_cur = RLIM_INFINITY;
        rl.rlim_max = RLIM_INFINITY;
    }

    unsigned long vm_size_kb = 0;
    unsigned long vm_rss_kb = 0;
    FILE* status = fopen("/proc/self/status", "r");
    if (status) {
        char line[256];
        while (fgets(line, sizeof(line), status)) {
            if (strncmp(line, "VmSize:", 7) == 0) {
                (void)sscanf(line + 7, "%lu", &vm_size_kb);
            } else if (strncmp(line, "VmRSS:", 6) == 0) {
                (void)sscanf(line + 6, "%lu", &vm_rss_kb);
            }
        }
        fclose(status);
    }
    // CRITICAL FIX: Do NOT decrement lock_depth yet!
    // fprintf() below may call malloc for buffering

    char rl_cur_buf[32];
    char rl_max_buf[32];
    if (rl.rlim_cur == RLIM_INFINITY) {
        strcpy(rl_cur_buf, "inf");
    } else {
        snprintf(rl_cur_buf, sizeof(rl_cur_buf), "%llu", (unsigned long long)rl.rlim_cur);
    }
    if (rl.rlim_max == RLIM_INFINITY) {
        strcpy(rl_max_buf, "inf");
    } else {
        snprintf(rl_max_buf, sizeof(rl_max_buf), "%llu", (unsigned long long)rl.rlim_max);
    }

#if !HAKMEM_BUILD_RELEASE
    fprintf(stderr,
            "[SS OOM] mmap failed: err=%d ss_size=%zu alloc_size=%zu "
            "RLIMIT_AS(cur=%s max=%s) VmSize=%lu kB VmRSS=%lu kB\n",
            err,
            ss_size,
            alloc_size,
            rl_cur_buf,
            rl_max_buf,
            vm_size_kb,
            vm_rss_kb);
#else
    (void)err; (void)ss_size; (void)alloc_size;
    (void)rl_cur_buf; (void)rl_max_buf;
    (void)vm_size_kb; (void)vm_rss_kb;
#endif

    g_hakmem_lock_depth--;  // Now safe to restore (all libc calls complete)
}

// ============================================================================
// OS Acquisition Implementation
// ============================================================================

void* ss_os_acquire(uint8_t size_class, size_t ss_size, uintptr_t ss_mask, int populate) {
    void* ptr = NULL;
    static int log_count = 0;

    (void)size_class;  // Used only for logging in debug builds

#ifdef MAP_ALIGNED_SUPER
    int map_flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_ALIGNED_SUPER;
#ifdef MAP_POPULATE
    if (populate) {
        map_flags |= MAP_POPULATE;
    }
#endif
    ptr = mmap(NULL, ss_size,
               PROT_READ | PROT_WRITE,
               map_flags,
               -1, 0);
    if (ptr != MAP_FAILED) {
        atomic_fetch_add(&g_ss_mmap_count, 1);
        if (((uintptr_t)ptr & ss_mask) == 0) {
            // Successfully got aligned pointer from OS
            return ptr;
        }
        munmap(ptr, ss_size);
        ptr = NULL;
    } else {
        log_superslab_oom_once(ss_size, ss_size, errno);
    }
#endif

    // Fallback: allocate 2x size and align manually
    // CRITICAL FIX (2025-12-05): Use MAP_POPULATE in fallback path
    // BUG: Previous code marked populate as unused, ignoring prefault request
    size_t alloc_size = ss_size * 2;
    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
#ifdef MAP_POPULATE
    if (populate) {
        flags |= MAP_POPULATE;
        static int dbg = 0;
        if (dbg < 3) {
            fprintf(stderr, "[SS_MMAP_DEBUG] populate=%d flags=0x%x (MAP_POPULATE=0x%x)\n",
                    populate, flags, MAP_POPULATE);
            dbg++;
        }
    }
#endif
    void* raw = mmap(NULL, alloc_size,
                     PROT_READ | PROT_WRITE,
                     flags,
                     -1, 0);
    if (raw != MAP_FAILED) {
        uint64_t count = atomic_fetch_add(&g_ss_mmap_count, 1) + 1;
        #if !HAKMEM_BUILD_RELEASE
        if (log_count < 10) {
            fprintf(stderr, "[SUPERSLAB_MMAP] #%lu: class=%d size=%zu (total SuperSlab mmaps so far)\n",
                    (unsigned long)count, size_class, ss_size);
            log_count++;
        }
        #else
        (void)log_count;
        #endif
    }
    if (raw == MAP_FAILED) {
        log_superslab_oom_once(ss_size, alloc_size, errno);
        return NULL;
    }

    uintptr_t raw_addr = (uintptr_t)raw;
    uintptr_t aligned_addr = (raw_addr + ss_mask) & ~ss_mask;
    ptr = (void*)aligned_addr;

    size_t prefix_size = aligned_addr - raw_addr;
    if (prefix_size > 0) {
        munmap(raw, prefix_size);
    }
    size_t suffix_size = alloc_size - prefix_size - ss_size;
    if (suffix_size > 0) {
        munmap((char*)ptr + ss_size, suffix_size);
    }

    // CRITICAL FIX (2025-12-05): Apply MADV_POPULATE_WRITE AFTER munmap trim
    // Issue: munmap() appears to undo MAP_POPULATE state on Linux 6.8.0-87
    // When mmap(4MB, MAP_POPULATE) is trimmed via munmap(prefix) + munmap(suffix),
    // the remaining 2MB middle region loses its "pages populated" flag.
    // Solution: Force re-population after trim using MADV_POPULATE_WRITE (Linux 5.14+)
    // See: EXPLICIT_PREFAULT_IMPLEMENTATION_REPORT_20251205.md
#ifdef MADV_POPULATE_WRITE
    if (populate) {
        int ret = madvise(ptr, ss_size, MADV_POPULATE_WRITE);
        if (ret != 0) {
            // Fallback for kernels that support MADV_POPULATE_WRITE but it fails
            // Use explicit page-by-page touching with writes
            volatile char* p = (volatile char*)ptr;
            for (size_t i = 0; i < ss_size; i += 4096) {
                p[i] = 0;
            }
            p[ss_size - 1] = 0;
        }
    }
#else
    if (populate) {
        // Fallback for kernels < 5.14: explicit page touch
        volatile char* p = (volatile char*)ptr;
        for (size_t i = 0; i < ss_size; i += 4096) {
            p[i] = 0;
        }
        p[ss_size - 1] = 0;
    }
#endif

    return ptr;
}