#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"

char buf[512];

void
cat(int fd)
{
  int n;

  while((n = read(fd, buf, sizeof(buf))) > 0) {
    if (write(1, buf, n) != n) {
      fprintf(2, "cat: write error\n");
      exit(1);
    }
  }
  if(n < 0){
    fprintf(2, "cat: read error\n");
    exit(1);
  }
}

int
main(int argc, char *argv[])
{
  int fd, i;

  if(argc <= 1){
    cat(0);
    exit(0);
  }

  for(i = 1; i < argc; i++){
    if((fd = open(argv[i], 0)) < 0){
      fprintf(2, "cat: cannot open %s\n", argv[i]);
      exit(1);
    }
    cat(fd);
    close(fd);
  }
  exit(0);
}

static uint64 (*syscalls[])(void) = {
[SYS_fork]    sys_fork,
[SYS_exit]    sys_exit,
[SYS_wait]    sys_wait,
[SYS_pipe]    sys_pipe,
[SYS_read]    sys_read,
[SYS_kill]    sys_kill,
[SYS_exec]    sys_exec,
[SYS_fstat]   sys_fstat,
[SYS_chdir]   sys_chdir,
[SYS_dup]     sys_dup,
[SYS_getpid]  sys_getpid,
[SYS_sbrk]    sys_sbrk,
[SYS_sleep]   sys_sleep,
[SYS_uptime]  sys_uptime,
[SYS_open]    sys_open,
[SYS_write]   sys_write,
[SYS_mknod]   sys_mknod,
[SYS_unlink]  sys_unlink,
[SYS_link]    sys_link,
[SYS_mkdir]   sys_mkdir,
[SYS_close]   sys_close,
};

void
syscall(void)
{
  int num;
  struct proc *p = myproc();

  num = p->trapframe->a7;
  if(num > 0 && num < NELEM(syscalls) && syscalls[num]) {
    p->trapframe->a0 = syscalls[num]();
  } else {
    printf("%d %s: unknown sys call %d\n",
            p->pid, p->name, num);
    p->trapframe->a0 = -1;
  }
}

uint64
sys_open(void)
{
  char path[MAXPATH];
  int fd, omode;
  struct file *f;
  struct inode *ip;
  int n;

  if((n = argstr(0, path, MAXPATH)) < 0 || argint(1, &omode) < 0)
    return -1;

  begin_op();

  if(omode & O_CREATE){ // 模式為創建新檔案
    ip = create(path, T_FILE, 0, 0); // 創建新的 inode
    if(ip == 0){
      end_op();
      return -1;
    }
  } else {
    if((ip = namei(path)) == 0){ // 取得該路徑名對應的 inode
      end_op();
      return -1;
    }
    ilock(ip); // 將該 inode 鎖定
    if(ip->type == T_DIR && omode != O_RDONLY){
      iunlockput(ip); // 若是目錄且要寫入，那就先解鎖該 inode
      end_op();
      return -1;
    }
  }

  if(ip->type == T_DEVICE && (ip->major < 0 || ip->major >= NDEV)){
    iunlockput(ip); // 若是裝置，那也先解鎖該 inode
    end_op();
    return -1;
  }

  if((f = filealloc()) == 0 || (fd = fdalloc(f)) < 0){ // 分配檔案描述子
    if(f) // 若分配失敗就關閉之。
      fileclose(f);
    iunlockput(ip); // 分配成功的話，先解鎖該 inode
    end_op();
    return -1;
  }
  // 設定 FILE (struct file) 結構 (也就是檔案描述子)
  if(ip->type == T_DEVICE){
    f->type = FD_DEVICE;
    f->major = ip->major;
  } else {
    f->type = FD_INODE;
    f->off = 0;
  }
  f->ip = ip;
  f->readable = !(omode & O_WRONLY);
  f->writable = (omode & O_WRONLY) || (omode & O_RDWR);

  if((omode & O_TRUNC) && ip->type == T_FILE){
    itrunc(ip); // 若是檔案且模式為 O_TRUNC，就將該 inode 清空。
  }

  iunlock(ip);
  end_op();

  return fd; // 傳回檔案描述子代碼 (在檔案表 ftable 中的位置)
}

uint64
sys_read(void)
{
  struct file *f;
  int n;
  uint64 p;

  if(argfd(0, 0, &f) < 0 || argint(2, &n) < 0 || argaddr(1, &p) < 0)
    return -1;
  return fileread(f, p, n);
}

// Read from file f.
// addr is a user virtual address.
int
fileread(struct file *f, uint64 addr, int n)
{
  int r = 0;

  if(f->readable == 0)
    return -1;

  if(f->type == FD_PIPE){
    r = piperead(f->pipe, addr, n);
  } else if(f->type == FD_DEVICE){
    if(f->major < 0 || f->major >= NDEV || !devsw[f->major].read)
      return -1;
    r = devsw[f->major].read(1, addr, n);
  } else if(f->type == FD_INODE){
    ilock(f->ip);
    if((r = readi(f->ip, 1, addr, f->off, n)) > 0)
      f->off += r;
    iunlock(f->ip);
  } else {
    panic("fileread");
  }

  return r;
}

// Disk layout:
// [ boot block | super block | log | inode blocks |
//                                          free bit map | data blocks]
//
// mkfs computes the super block and builds an initial file system. The
// super block describes the disk layout:
struct superblock { // 超級區塊
  uint magic;        // Must be FSMAGIC      // 用來辨識的魔數:0x10203040
  uint size;         // Size of file system image (blocks) // 全部區塊數
  uint nblocks;      // Number of data blocks // 資料區塊數
  uint ninodes;      // Number of inodes.     // inodes 數量
  uint nlog;         // Number of log blocks  // 日誌 log 的區塊數
  uint logstart;     // Block number of first log block   // log 的首區塊
  uint inodestart;   // Block number of first inode block // inode 的首區塊
  uint bmapstart;    // Block number of first free map block // free bitmap 的首區塊
};

#define FSMAGIC 0x10203040

// in-memory copy of an inode
struct inode {
  uint dev;           // Device number
  uint inum;          // Inode number
  int ref;            // Reference count
  struct sleeplock lock; // protects everything below here
  int valid;          // inode has been read from disk?

  short type;         // copy of disk inode
  short major;
  short minor;
  short nlink;
  uint size;
  uint addrs[NDIRECT+1];
};

#define NDIRECT 12
#define NINDIRECT (BSIZE / sizeof(uint))
#define MAXFILE (NDIRECT + NINDIRECT)

// On-disk inode structure
struct dinode {
  short type;           // File type
  short major;          // Major device number (T_DEVICE only)
  short minor;          // Minor device number (T_DEVICE only)
  short nlink;          // Number of links to inode in file system
  uint size;            // Size of file (bytes)
  uint addrs[NDIRECT+1];   // Data block addresses
};

// Read data from inode.
// Caller must hold ip->lock.
// If user_dst==1, then dst is a user virtual address;
// otherwise, dst is a kernel address.
int
readi(struct inode *ip, int user_dst, uint64 dst, uint off, uint n)
{
  uint tot, m;
  struct buf *bp;

  if(off > ip->size || off + n < off)
    return 0;
  if(off + n > ip->size)
    n = ip->size - off;

  for(tot=0; tot<n; tot+=m, off+=m, dst+=m){
    bp = bread(ip->dev, bmap(ip, off/BSIZE));
    m = min(n - tot, BSIZE - off%BSIZE);
    if(either_copyout(user_dst, dst, bp->data + (off % BSIZE), m) == -1) {
      brelse(bp);
      tot = -1;
      break;
    }
    brelse(bp);
  }
  return tot;
}

struct {
  struct spinlock lock;
  struct buf buf[NBUF];

  // Linked list of all buffers, through prev/next.
  // Sorted by how recently the buffer was used.
  // head.next is most recent, head.prev is least.
  struct buf head;
} bcache;

// Return a locked buf with the contents of the indicated block.
struct buf*
bread(uint dev, uint blockno)
{
  struct buf *b;

  b = bget(dev, blockno);
  if(!b->valid) {
    virtio_disk_rw(b, 0);
    b->valid = 1;
  }
  return b;
}

// 參考 [Virtual I/O Device (VIRTIO) Version 1.1 -- 4.2.2 MMIO Device Register Layout](https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html#x1-1460002)
void
virtio_disk_init(void) // 初始化本模組
{
  uint32 status = 0;

  initlock(&disk.vdisk_lock, "virtio_disk");

  // 檢查是否有 MMIO 磁碟裝置存在？
  if(*R(VIRTIO_MMIO_MAGIC_VALUE) != 0x74726976 ||
     *R(VIRTIO_MMIO_VERSION) != 1 ||
     *R(VIRTIO_MMIO_DEVICE_ID) != 2 ||
     *R(VIRTIO_MMIO_VENDOR_ID) != 0x554d4551){
    panic("could not find virtio disk");
  }
  
  // 設定 VIRTIO_MMIO 狀態
  status |= VIRTIO_CONFIG_S_ACKNOWLEDGE;
  *R(VIRTIO_MMIO_STATUS) = status;

  status |= VIRTIO_CONFIG_S_DRIVER;
  *R(VIRTIO_MMIO_STATUS) = status;

  // negotiate features // 設定 feature 準備開始協商
  uint64 features = *R(VIRTIO_MMIO_DEVICE_FEATURES);
  features &= ~(1 << VIRTIO_BLK_F_RO);
  features &= ~(1 << VIRTIO_BLK_F_SCSI);
  features &= ~(1 << VIRTIO_BLK_F_CONFIG_WCE);
  features &= ~(1 << VIRTIO_BLK_F_MQ);
  features &= ~(1 << VIRTIO_F_ANY_LAYOUT);
  features &= ~(1 << VIRTIO_RING_F_EVENT_IDX);
  features &= ~(1 << VIRTIO_RING_F_INDIRECT_DESC);
  *R(VIRTIO_MMIO_DRIVER_FEATURES) = features;

  // tell device that feature negotiation is complete.
  status |= VIRTIO_CONFIG_S_FEATURES_OK; // feature 設定好了
  *R(VIRTIO_MMIO_STATUS) = status;

  // tell device we're completely ready. // 完成準備，要求 QEMU 協商
  status |= VIRTIO_CONFIG_S_DRIVER_OK;
  *R(VIRTIO_MMIO_STATUS) = status;

  *R(VIRTIO_MMIO_GUEST_PAGE_SIZE) = PGSIZE;

  // initialize queue 0.
  *R(VIRTIO_MMIO_QUEUE_SEL) = 0;
  uint32 max = *R(VIRTIO_MMIO_QUEUE_NUM_MAX);
  if(max == 0)
    panic("virtio disk has no queue 0");
  if(max < NUM)
    panic("virtio disk max queue too short");
  *R(VIRTIO_MMIO_QUEUE_NUM) = NUM;
  memset(disk.pages, 0, sizeof(disk.pages));
  *R(VIRTIO_MMIO_QUEUE_PFN) = ((uint64)disk.pages) >> PGSHIFT; // PFN: Guest physical page number of the virtual queue

  // desc = pages -- num * virtq_desc
  // avail = pages + 0x40 -- 2 * uint16, then num * uint16
  // used = pages + 4096 -- 2 * uint16, then num * vRingUsedElem

  disk.desc = (struct virtq_desc *) disk.pages;
  disk.avail = (struct virtq_avail *)(disk.pages + NUM*sizeof(struct virtq_desc));
  disk.used = (struct virtq_used *) (disk.pages + PGSIZE);

  // all NUM descriptors start out unused. // 設定所有描述子均為可用
  for(int i = 0; i < NUM; i++)
    disk.free[i] = 1;

  // plic.c and trap.c arrange for interrupts from VIRTIO0_IRQ.
}

// find a free descriptor, mark it non-free, return its index.
static int
alloc_desc() // 找到一個可用的 free descriptor 分配之
{
  for(int i = 0; i < NUM; i++){
    if(disk.free[i]){
      disk.free[i] = 0;
      return i;
    }
  }
  return -1;
}

// mark a descriptor as free.
static void
free_desc(int i) // 歸還 descriptor ，回到 free 狀態
{
  if(i >= NUM)
    panic("free_desc 1");
  if(disk.free[i])
    panic("free_desc 2");
  disk.desc[i].addr = 0;
  disk.desc[i].len = 0;
  disk.desc[i].flags = 0;
  disk.desc[i].next = 0;
  disk.free[i] = 1;
  wakeup(&disk.free[0]);
}

// free a chain of descriptors.
static void
free_chain(int i) // 釋放一整條的鍊 (descriptor chain)
{
  while(1){
    int flag = disk.desc[i].flags;
    int nxt = disk.desc[i].next;
    free_desc(i);
    if(flag & VRING_DESC_F_NEXT)
      i = nxt;
    else
      break;
  }
}

// allocate three descriptors (they need not be contiguous).
// disk transfers always use three descriptors.
static int
alloc3_desc(int *idx) // 分配空間連續的 3 個 descriptor
{
  for(int i = 0; i < 3; i++){
    idx[i] = alloc_desc();
    if(idx[i] < 0){
      for(int j = 0; j < i; j++)
        free_desc(idx[j]);
      return -1;
    }
  }
  return 0;
}

void
virtio_disk_rw(struct buf *b, int write) // 啟動 virtio 的磁碟寫入動作
{
  uint64 sector = b->blockno * (BSIZE / 512);

  acquire(&disk.vdisk_lock);

  // the spec's Section 5.2 says that legacy block operations use
  // three descriptors: one for type/reserved/sector, one for the
  // data, one for a 1-byte status result.

  // allocate the three descriptors. // 分配直到成功為止
  int idx[3];
  while(1){
    if(alloc3_desc(idx) == 0) {
      break;
    }
    sleep(&disk.free[0], &disk.vdisk_lock);
  }

  // format the three descriptors.
  // qemu's virtio-blk.c reads them.
  // 參考 -- https://github.com/qemu/qemu/blob/master/hw/block/virtio-blk.c

  struct virtio_blk_req *buf0 = &disk.ops[idx[0]]; // 讀寫的區塊

  if(write) // 根據 write 來設定為《寫入或讀取》
    buf0->type = VIRTIO_BLK_T_OUT; // write the disk // 讀寫類型為寫入
  else
    buf0->type = VIRTIO_BLK_T_IN; // read the disk // 讀寫類型為讀取
  buf0->reserved = 0;
  buf0->sector = sector; // 讀寫的磁區號碼 (sector)

  // 第 0 個描述子
  disk.desc[idx[0]].addr = (uint64) buf0;
  disk.desc[idx[0]].len = sizeof(struct virtio_blk_req);
  disk.desc[idx[0]].flags = VRING_DESC_F_NEXT;
  disk.desc[idx[0]].next = idx[1];

  // 第 1 個描述子
  disk.desc[idx[1]].addr = (uint64) b->data;
  disk.desc[idx[1]].len = BSIZE;
  if(write)
    disk.desc[idx[1]].flags = 0; // device reads b->data
  else
    disk.desc[idx[1]].flags = VRING_DESC_F_WRITE; // device writes b->data
  disk.desc[idx[1]].flags |= VRING_DESC_F_NEXT;
  disk.desc[idx[1]].next = idx[2];

  // 第 2 個描述子
  disk.info[idx[0]].status = 0xff; // device writes 0 on success
  disk.desc[idx[2]].addr = (uint64) &disk.info[idx[0]].status;
  disk.desc[idx[2]].len = 1;
  disk.desc[idx[2]].flags = VRING_DESC_F_WRITE; // device writes the status
  disk.desc[idx[2]].next = 0;

  // record struct buf for virtio_disk_intr().
  b->disk = 1;
  disk.info[idx[0]].b = b;

  // tell the device the first index in our chain of descriptors.
  disk.avail->ring[disk.avail->idx % NUM] = idx[0];

  __sync_synchronize();

  // tell the device another avail ring entry is available.
  disk.avail->idx += 1; // not % NUM ...

  __sync_synchronize();

  *R(VIRTIO_MMIO_QUEUE_NOTIFY) = 0; // value is queue number

  // Wait for virtio_disk_intr() to say request has finished.
  while(b->disk == 1) { // b->disk=1 代表磁碟正在讀取到緩衝區 buf
    sleep(b, &disk.vdisk_lock);
  }

  // 讀完了，釋放 idx[0]
  disk.info[idx[0]].b = 0;
  free_chain(idx[0]);

  release(&disk.vdisk_lock);
}

void
virtio_disk_intr() // virtio_disk_rw() 請求讀寫，完成後 qemu 會發中斷給 xv6
{
  acquire(&disk.vdisk_lock);

  // the device won't raise another interrupt until we tell it
  // we've seen this interrupt, which the following line does.
  // this may race with the device writing new entries to
  // the "used" ring, in which case we may process the new
  // completion entries in this interrupt, and have nothing to do
  // in the next interrupt, which is harmless.
  *R(VIRTIO_MMIO_INTERRUPT_ACK) = *R(VIRTIO_MMIO_INTERRUPT_STATUS) & 0x3;

  __sync_synchronize();

  // the device increments disk.used->idx when it
  // adds an entry to the used ring.

  while(disk.used_idx != disk.used->idx){
    __sync_synchronize();
    int id = disk.used->ring[disk.used_idx % NUM].id;

    if(disk.info[id].status != 0)
      panic("virtio_disk_intr status");

    struct buf *b = disk.info[id].b;
    b->disk = 0;   // disk is done with buf
    wakeup(b); // 讀取完成，喚醒等待此磁碟事件的行程 (加入排程佇列)

    disk.used_idx += 1;
  }

  release(&disk.vdisk_lock);
}