--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/fs.c	Fri May 26 23:11:05 2017 +0900
@@ -0,0 +1,707 @@
+// File system implementation.  Five layers:
+//   + Blocks: allocator for raw disk blocks.
+//   + Log: crash recovery for multi-step updates.
+//   + Files: inode allocator, reading, writing, metadata.
+//   + Directories: inode with special contents (list of other inodes!)
+//   + Names: paths like /usr/rtm/xv6/fs.c for convenient naming.
+//
+// This file contains the low-level file system manipulation
+// routines.  The (higher-level) system call implementations
+// are in sysfile.c.
+
+#include "types.h"
+#include "defs.h"
+#include "param.h"
+#include "stat.h"
+#include "mmu.h"
+#include "proc.h"
+#include "spinlock.h"
+#include "buf.h"
+#include "fs.h"
+#include "file.h"
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+static void itrunc (struct inode*);
+
+// Read the super block.
+void readsb (int dev, struct superblock *sb)
+{
+    struct buf *bp;
+
+    bp = bread(dev, 1);
+    memmove(sb, bp->data, sizeof(*sb));
+    brelse(bp);
+}
+
+// Zero a block.
+static void bzero (int dev, int bno)
+{
+    struct buf *bp;
+
+    bp = bread(dev, bno);
+    memset(bp->data, 0, BSIZE);
+    log_write(bp);
+    brelse(bp);
+}
+
+// Blocks.
+
+// Allocate a zeroed disk block.
+static uint balloc (uint dev)
+{
+    int b, bi, m;
+    struct buf *bp;
+    struct superblock sb;
+
+    bp = 0;
+    readsb(dev, &sb);
+
+    for (b = 0; b < sb.size; b += BPB) {
+        bp = bread(dev, BBLOCK(b, sb.ninodes));
+
+        for (bi = 0; bi < BPB && b + bi < sb.size; bi++) {
+            m = 1 << (bi % 8);
+
+            if ((bp->data[bi / 8] & m) == 0) {  // Is block free?
+                bp->data[bi / 8] |= m;  // Mark block in use.
+                log_write(bp);
+                brelse(bp);
+                bzero(dev, b + bi);
+                return b + bi;
+            }
+        }
+
+        brelse(bp);
+    }
+
+    panic("balloc: out of blocks");
+}
+
+// Free a disk block.
+static void bfree (int dev, uint b)
+{
+    struct buf *bp;
+    struct superblock sb;
+    int bi, m;
+
+    readsb(dev, &sb);
+    bp = bread(dev, BBLOCK(b, sb.ninodes));
+    bi = b % BPB;
+    m = 1 << (bi % 8);
+
+    if ((bp->data[bi / 8] & m) == 0) {
+        panic("freeing free block");
+    }
+
+    bp->data[bi / 8] &= ~m;
+    log_write(bp);
+    brelse(bp);
+}
+
+// Inodes.
+//
+// An inode describes a single unnamed file.
+// The inode disk structure holds metadata: the file's type,
+// its size, the number of links referring to it, and the
+// list of blocks holding the file's content.
+//
+// The inodes are laid out sequentially on disk immediately after
+// the superblock. Each inode has a number, indicating its
+// position on the disk.
+//
+// The kernel keeps a cache of in-use inodes in memory
+// to provide a place for synchronizing access
+// to inodes used by multiple processes. The cached
+// inodes include book-keeping information that is
+// not stored on disk: ip->ref and ip->flags.
+//
+// An inode and its in-memory represtative go through a
+// sequence of states before they can be used by the
+// rest of the file system code.
+//
+// * Allocation: an inode is allocated if its type (on disk)
+//   is non-zero. ialloc() allocates, iput() frees if
+//   the link count has fallen to zero.
+//
+// * Referencing in cache: an entry in the inode cache
+//   is free if ip->ref is zero. Otherwise ip->ref tracks
+//   the number of in-memory pointers to the entry (open
+//   files and current directories). iget() to find or
+//   create a cache entry and increment its ref, iput()
+//   to decrement ref.
+//
+// * Valid: the information (type, size, &c) in an inode
+//   cache entry is only correct when the I_VALID bit
+//   is set in ip->flags. ilock() reads the inode from
+//   the disk and sets I_VALID, while iput() clears
+//   I_VALID if ip->ref has fallen to zero.
+//
+// * Locked: file system code may only examine and modify
+//   the information in an inode and its content if it
+//   has first locked the inode. The I_BUSY flag indicates
+//   that the inode is locked. ilock() sets I_BUSY,
+//   while iunlock clears it.
+//
+// Thus a typical sequence is:
+//   ip = iget(dev, inum)
+//   ilock(ip)
+//   ... examine and modify ip->xxx ...
+//   iunlock(ip)
+//   iput(ip)
+//
+// ilock() is separate from iget() so that system calls can
+// get a long-term reference to an inode (as for an open file)
+// and only lock it for short periods (e.g., in read()).
+// The separation also helps avoid deadlock and races during
+// pathname lookup. iget() increments ip->ref so that the inode
+// stays cached and pointers to it remain valid.
+//
+// Many internal file system functions expect the caller to
+// have locked the inodes involved; this lets callers create
+// multi-step atomic operations.
+
+struct {
+    struct spinlock lock;
+    struct inode inode[NINODE];
+} icache;
+
+void iinit (void)
+{
+    initlock(&icache.lock, "icache");
+}
+
+static struct inode* iget (uint dev, uint inum);
+
+//PAGEBREAK!
+// Allocate a new inode with the given type on device dev.
+// A free inode has a type of zero.
+struct inode* ialloc (uint dev, short type)
+{
+    int inum;
+    struct buf *bp;
+    struct dinode *dip;
+    struct superblock sb;
+
+    readsb(dev, &sb);
+
+    for (inum = 1; inum < sb.ninodes; inum++) {
+        bp = bread(dev, IBLOCK(inum));
+        dip = (struct dinode*) bp->data + inum % IPB;
+
+        if (dip->type == 0) {  // a free inode
+            memset(dip, 0, sizeof(*dip));
+            dip->type = type;
+            log_write(bp);   // mark it allocated on the disk
+            brelse(bp);
+            return iget(dev, inum);
+        }
+
+        brelse(bp);
+    }
+
+    panic("ialloc: no inodes");
+}
+
+// Copy a modified in-memory inode to disk.
+void iupdate (struct inode *ip)
+{
+    struct buf *bp;
+    struct dinode *dip;
+
+    bp = bread(ip->dev, IBLOCK(ip->inum));
+
+    dip = (struct dinode*) bp->data + ip->inum % IPB;
+    dip->type = ip->type;
+    dip->major = ip->major;
+    dip->minor = ip->minor;
+    dip->nlink = ip->nlink;
+    dip->size = ip->size;
+
+    memmove(dip->addrs, ip->addrs, sizeof(ip->addrs));
+    log_write(bp);
+    brelse(bp);
+}
+
+// Find the inode with number inum on device dev
+// and return the in-memory copy. Does not lock
+// the inode and does not read it from disk.
+static struct inode* iget (uint dev, uint inum)
+{
+    struct inode *ip, *empty;
+
+    acquire(&icache.lock);
+
+    // Is the inode already cached?
+    empty = 0;
+
+    for (ip = &icache.inode[0]; ip < &icache.inode[NINODE]; ip++) {
+        if (ip->ref > 0 && ip->dev == dev && ip->inum == inum) {
+            ip->ref++;
+            release(&icache.lock);
+            return ip;
+        }
+
+        if (empty == 0 && ip->ref == 0) {   // Remember empty slot.
+            empty = ip;
+        }
+    }
+
+    // Recycle an inode cache entry.
+    if (empty == 0) {
+        panic("iget: no inodes");
+    }
+
+    ip = empty;
+    ip->dev = dev;
+    ip->inum = inum;
+    ip->ref = 1;
+    ip->flags = 0;
+    release(&icache.lock);
+
+    return ip;
+}
+
+// Increment reference count for ip.
+// Returns ip to enable ip = idup(ip1) idiom.
+struct inode* idup (struct inode *ip)
+{
+    acquire(&icache.lock);
+    ip->ref++;
+    release(&icache.lock);
+    return ip;
+}
+
+// Lock the given inode.
+// Reads the inode from disk if necessary.
+void ilock (struct inode *ip)
+{
+    struct buf *bp;
+    struct dinode *dip;
+
+    if (ip == 0 || ip->ref < 1) {
+        panic("ilock");
+    }
+
+    acquire(&icache.lock);
+    while (ip->flags & I_BUSY) {
+        sleep(ip, &icache.lock);
+    }
+
+    ip->flags |= I_BUSY;
+    release(&icache.lock);
+
+    if (!(ip->flags & I_VALID)) {
+        bp = bread(ip->dev, IBLOCK(ip->inum));
+
+        dip = (struct dinode*) bp->data + ip->inum % IPB;
+        ip->type = dip->type;
+        ip->major = dip->major;
+        ip->minor = dip->minor;
+        ip->nlink = dip->nlink;
+        ip->size = dip->size;
+
+        memmove(ip->addrs, dip->addrs, sizeof(ip->addrs));
+        brelse(bp);
+        ip->flags |= I_VALID;
+
+        if (ip->type == 0) {
+            panic("ilock: no type");
+        }
+    }
+}
+
+// Unlock the given inode.
+void iunlock (struct inode *ip)
+{
+    if (ip == 0 || !(ip->flags & I_BUSY) || ip->ref < 1) {
+        panic("iunlock");
+    }
+
+    acquire(&icache.lock);
+    ip->flags &= ~I_BUSY;
+    wakeup(ip);
+    release(&icache.lock);
+}
+
+// Drop a reference to an in-memory inode.
+// If that was the last reference, the inode cache entry can
+// be recycled.
+// If that was the last reference and the inode has no links
+// to it, free the inode (and its content) on disk.
+void iput (struct inode *ip)
+{
+    acquire(&icache.lock);
+
+    if (ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0) {
+        // inode has no links: truncate and free inode.
+        if (ip->flags & I_BUSY) {
+            panic("iput busy");
+        }
+
+        ip->flags |= I_BUSY;
+        release(&icache.lock);
+        itrunc(ip);
+        ip->type = 0;
+        iupdate(ip);
+
+        acquire(&icache.lock);
+        ip->flags = 0;
+        wakeup(ip);
+    }
+
+    ip->ref--;
+    release(&icache.lock);
+}
+
+// Common idiom: unlock, then put.
+void iunlockput (struct inode *ip)
+{
+    iunlock(ip);
+    iput(ip);
+}
+
+//PAGEBREAK!
+// Inode content
+//
+// The content (data) associated with each inode is stored
+// in blocks on the disk. The first NDIRECT block numbers
+// are listed in ip->addrs[].  The next NINDIRECT blocks are
+// listed in block ip->addrs[NDIRECT].
+
+// Return the disk block address of the nth block in inode ip.
+// If there is no such block, bmap allocates one.
+static uint bmap (struct inode *ip, uint bn)
+{
+    uint addr, *a;
+    struct buf *bp;
+
+    if (bn < NDIRECT) {
+        if ((addr = ip->addrs[bn]) == 0) {
+            ip->addrs[bn] = addr = balloc(ip->dev);
+        }
+
+        return addr;
+    }
+
+    bn -= NDIRECT;
+
+    if (bn < NINDIRECT) {
+        // Load indirect block, allocating if necessary.
+        if ((addr = ip->addrs[NDIRECT]) == 0) {
+            ip->addrs[NDIRECT] = addr = balloc(ip->dev);
+        }
+
+        bp = bread(ip->dev, addr);
+        a = (uint*) bp->data;
+
+        if ((addr = a[bn]) == 0) {
+            a[bn] = addr = balloc(ip->dev);
+            log_write(bp);
+        }
+
+        brelse(bp);
+        return addr;
+    }
+
+    panic("bmap: out of range");
+}
+
+// Truncate inode (discard contents).
+// Only called when the inode has no links
+// to it (no directory entries referring to it)
+// and has no in-memory reference to it (is
+// not an open file or current directory).
+static void itrunc (struct inode *ip)
+{
+    int i, j;
+    struct buf *bp;
+    uint *a;
+
+    for (i = 0; i < NDIRECT; i++) {
+        if (ip->addrs[i]) {
+            bfree(ip->dev, ip->addrs[i]);
+            ip->addrs[i] = 0;
+        }
+    }
+
+    if (ip->addrs[NDIRECT]) {
+        bp = bread(ip->dev, ip->addrs[NDIRECT]);
+        a = (uint*) bp->data;
+
+        for (j = 0; j < NINDIRECT; j++) {
+            if (a[j]) {
+                bfree(ip->dev, a[j]);
+            }
+        }
+
+        brelse(bp);
+        bfree(ip->dev, ip->addrs[NDIRECT]);
+        ip->addrs[NDIRECT] = 0;
+    }
+
+    ip->size = 0;
+    iupdate(ip);
+}
+
+// Copy stat information from inode.
+void stati (struct inode *ip, struct stat *st)
+{
+    st->dev = ip->dev;
+    st->ino = ip->inum;
+    st->type = ip->type;
+    st->nlink = ip->nlink;
+    st->size = ip->size;
+}
+
+//PAGEBREAK!
+// Read data from inode.
+int readi (struct inode *ip, char *dst, uint off, uint n)
+{
+    uint tot, m;
+    struct buf *bp;
+
+    if (ip->type == T_DEV) {
+        if (ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].read) {
+            return -1;
+        }
+
+        return devsw[ip->major].read(ip, dst, n);
+    }
+
+    if (off > ip->size || off + n < off) {
+        return -1;
+    }
+
+    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);
+        memmove(dst, bp->data + off % BSIZE, m);
+        brelse(bp);
+    }
+
+    return n;
+}
+
+// PAGEBREAK!
+// Write data to inode.
+int writei (struct inode *ip, char *src, uint off, uint n)
+{
+    uint tot, m;
+    struct buf *bp;
+
+    if (ip->type == T_DEV) {
+        if (ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].write) {
+            return -1;
+        }
+
+        return devsw[ip->major].write(ip, src, n);
+    }
+
+    if (off > ip->size || off + n < off) {
+        return -1;
+    }
+
+    if (off + n > MAXFILE * BSIZE) {
+        return -1;
+    }
+
+    for (tot = 0; tot < n; tot += m, off += m, src += m) {
+        bp = bread(ip->dev, bmap(ip, off / BSIZE));
+        m = min(n - tot, BSIZE - off%BSIZE);
+        memmove(bp->data + off % BSIZE, src, m);
+        log_write(bp);
+        brelse(bp);
+    }
+
+    if (n > 0 && off > ip->size) {
+        ip->size = off;
+        iupdate(ip);
+    }
+
+    return n;
+}
+
+//PAGEBREAK!
+// Directories
+
+int namecmp (const char *s, const char *t)
+{
+    return strncmp(s, t, DIRSIZ);
+}
+
+// Look for a directory entry in a directory.
+// If found, set *poff to byte offset of entry.
+struct inode* dirlookup (struct inode *dp, char *name, uint *poff)
+{
+    uint off, inum;
+    struct dirent de;
+
+    if (dp->type != T_DIR) {
+        panic("dirlookup not DIR");
+    }
+
+    for (off = 0; off < dp->size; off += sizeof(de)) {
+        if (readi(dp, (char*) &de, off, sizeof(de)) != sizeof(de)) {
+            panic("dirlink read");
+        }
+
+        if (de.inum == 0) {
+            continue;
+        }
+
+        if (namecmp(name, de.name) == 0) {
+            // entry matches path element
+            if (poff) {
+                *poff = off;
+            }
+
+            inum = de.inum;
+            return iget(dp->dev, inum);
+        }
+    }
+
+    return 0;
+}
+
+// Write a new directory entry (name, inum) into the directory dp.
+int dirlink (struct inode *dp, char *name, uint inum)
+{
+    int off;
+    struct dirent de;
+    struct inode *ip;
+
+    // Check that name is not present.
+    if ((ip = dirlookup(dp, name, 0)) != 0) {
+        iput(ip);
+        return -1;
+    }
+
+    // Look for an empty dirent.
+    for (off = 0; off < dp->size; off += sizeof(de)) {
+        if (readi(dp, (char*) &de, off, sizeof(de)) != sizeof(de)) {
+            panic("dirlink read");
+        }
+
+        if (de.inum == 0) {
+            break;
+        }
+    }
+
+    strncpy(de.name, name, DIRSIZ);
+    de.inum = inum;
+
+    if (writei(dp, (char*) &de, off, sizeof(de)) != sizeof(de)) {
+        panic("dirlink");
+    }
+
+    return 0;
+}
+
+//PAGEBREAK!
+// Paths
+
+// Copy the next path element from path into name.
+// Return a pointer to the element following the copied one.
+// The returned path has no leading slashes,
+// so the caller can check *path=='\0' to see if the name is the last one.
+// If no name to remove, return 0.
+//
+// Examples:
+//   skipelem("a/bb/c", name) = "bb/c", setting name = "a"
+//   skipelem("///a//bb", name) = "bb", setting name = "a"
+//   skipelem("a", name) = "", setting name = "a"
+//   skipelem("", name) = skipelem("////", name) = 0
+//
+static char* skipelem (char *path, char *name)
+{
+    char *s;
+    int len;
+
+    while (*path == '/') {
+        path++;
+    }
+
+    if (*path == 0) {
+        return 0;
+    }
+
+    s = path;
+
+    while (*path != '/' && *path != 0) {
+        path++;
+    }
+
+    len = path - s;
+
+    if (len >= DIRSIZ) {
+        memmove(name, s, DIRSIZ);
+    } else {
+        memmove(name, s, len);
+        name[len] = 0;
+    }
+
+    while (*path == '/') {
+        path++;
+    }
+
+    return path;
+}
+
+// Look up and return the inode for a path name.
+// If parent != 0, return the inode for the parent and copy the final
+// path element into name, which must have room for DIRSIZ bytes.
+static struct inode* namex (char *path, int nameiparent, char *name)
+{
+    struct inode *ip, *next;
+
+    if (*path == '/') {
+        ip = iget(ROOTDEV, ROOTINO);
+    } else {
+        ip = idup(proc->cwd);
+    }
+
+    while ((path = skipelem(path, name)) != 0) {
+        ilock(ip);
+
+        if (ip->type != T_DIR) {
+            iunlockput(ip);
+            return 0;
+        }
+
+        if (nameiparent && *path == '\0') {
+            // Stop one level early.
+            iunlock(ip);
+            return ip;
+        }
+
+        if ((next = dirlookup(ip, name, 0)) == 0) {
+            iunlockput(ip);
+            return 0;
+        }
+
+        iunlockput(ip);
+        ip = next;
+    }
+
+    if (nameiparent) {
+        iput(ip);
+        return 0;
+    }
+
+    return ip;
+}
+
+struct inode* namei (char *path)
+{
+    char name[DIRSIZ];
+    return namex(path, 0, name);
+}
+
+struct inode* nameiparent (char *path, char *name)
+{
+    return namex(path, 1, name);
+}