inode.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include <u.h>
#include <libc.h>
#include "cformat.h"
#include "lru.h"
#include "bcache.h"
#include "disk.h"
#include "inode.h"
#include "stats.h"

/*
 *  read the inode blocks and make sure they
 *  haven't been trashed.
 *
 *  make the in-core table of qid to inode mappings.
 *	N.B. this is just an array. we need a linear search to find
 *	     a particular inode. this could be done faster.
 *
 *  nab is the first inode block.
 */
int
iinit(Icache *ic, int f, int psize)
{
	Ibuf *b;
	Imap *m;
	ulong ino;
	Bbuf *bb;
	Dinode *bi;

	/*
	 *  get basic sizes and allocation info from disk
	 */
	if(dinit(ic, f, psize) < 0)
		return -1;

	/*
	 *  read first inode block to get number of inodes
	 */
	bb = bcread(ic, ic->nab);
	if(bb == 0){
		fprint(2, "iinit: can't read disk\n");
		return -1;
	}
	bi = (Dinode*)bb->data;
	if(bi->nino==0 || bi->nino>2048){
		fprint(2, "iinit: bad nino\n");
		return -1;
	}
	ic->nino = bi->nino;

	/*
	 *  set up sizing constants
	 */
	ic->i2b = (ic->bsize - sizeof(Dihdr))/sizeof(Inode);
	ic->nib = (ic->nino + ic->i2b - 1)/ic->i2b;

	/*
	 *  allocate the in-core qid/inode map, build it's lru
	 */
	if(ic->map)
		free(ic->map);
	ic->map = malloc(sizeof(Imap)*ic->nino);
	if(ic->map == 0){
		fprint(2, "iinit: can't alloc map\n");
		return -1;
	}
	lruinit(&ic->mlru);
	for(m = ic->map; m < &ic->map[ic->nino]; m++){
		m->inuse = 0;
		m->b = 0;
		lruadd(&ic->mlru, m);
	}

	/*
	 *  mark all cache buffers as empty, put them on the lru list
	 */
	lruinit(&ic->blru);
	for(b = ic->ib; b < &ic->ib[Nicache]; b++){
		b->inuse = 0;
		lruadd(&ic->blru, b);
	}

	/*
	 *  Read all inodes and
	 *  build the in-core qid/inode map
	 */
	for(ino = 0; ino < ic->nino; ino++){
		b = iread(ic, ino);
		if(b == 0){
			fprint(2, "iinit: can't read inode %ld\n", ino);
			return -1;
		}
		if(b->inode.inuse){
			m = &ic->map[ino];
			m->inuse = 1;
			m->qid = b->inode.qid;
			lruref(&ic->mlru, m);
		}
	}
	return 0;
}

/*
 *  format the inode blocks
 */
int
iformat(Icache *ic, int f, ulong nino, char *name, int bsize, int psize)
{
	Bbuf *bb;
	Dinode *bi;
	ulong bno;
	ulong i;
	ulong i2b;
	int nib;

	/*
	 *  first format disk allocation
	 */
	if(dformat(ic, f, name, bsize, psize) < 0)
		return -1;

	fprint(2, "formatting inodes\n");

	i2b = (bsize - sizeof(Dihdr))/sizeof(Inode);
	nib = (nino + i2b - 1)/i2b;

	for(bno = ic->nab; bno < ic->nab + nib; bno++){
		if(dalloc(ic, 0) == Notabno){
			fprint(2, "iformat: balloc failed\n");
			return -1;
		}
		bb = bcalloc(ic, bno);
		if(bb == 0){
			fprint(2, "iformat: bcalloc failed\n");
			return -1;
		}
		bi = (Dinode*)bb->data;
		bi->magic = Imagic;
		bi->nino = nino;
		for(i = 0; i < i2b; i++)
			bi->inode[i].inuse = 0;
		bcmark(ic, bb);
	}

	bcsync(ic);

	return iinit(ic, f, psize);
}

/*
 *  allocate a cache buffer, use least recently used
 */
Ibuf*
ialloc(Icache *ic, ulong ino)
{
	Imap *m;
	Ibuf *b;

	b = (Ibuf*)ic->blru.lnext;
	if(b->inuse)
		ic->map[b->ino].b = 0;
	b->ino = ino;
	b->inuse = 1;
	m = &ic->map[ino];
	m->b = b;
	return b;
}

/*
 *  free a cache buffer
 */
void
ifree(Icache *ic, Ibuf *b)
{
	b->inuse = 0;
	if(b->inuse)
		ic->map[b->ino].b = 0;
	lruderef(&ic->blru, b);
}

/*
 *  get an inode into the cache.  if no inode exists for this qid, create one
 *  from an unused qid/inode map.
 */
Ibuf *
iget(Icache *ic, Qid qid)
{
	Imap *m, *me;
	Ibuf *b;

	/*
	 *  find map entry with same qid.path
	 */
	for(m = ic->map, me = &ic->map[ic->nino]; m < me; m++){
		if(m->inuse && m->qid.path==qid.path){
			if(m->qid.vers != qid.vers){
				/*
				 *  our info is old, forget it
				 */
				DPRINT(2, "updating old file %llud.%lud\n",
					qid.path, qid.vers);
				m->qid = qid;
				iupdate(ic, m - ic->map, qid);
			}
			break;
		}
	}

	/*
 	 *  if an already existing inode, just get it
	 */
	if(m != me)
		return iread(ic, m - ic->map);

	/*
	 *  create a new inode, throw out the least recently used inode
	 *  if necessary
	 */
	m = (Imap*)ic->mlru.lnext;
	if(m->inuse){
		DPRINT(2, "superceding file %llud.%ld by %llud.%ld\n", m->qid.path,
			m->qid.vers, qid.path, qid.vers);
		if(iremove(ic, m - ic->map) < 0)
			return 0;
	}

	if(statson){
		cfsstat.ninsert++;
	}
	/*
	 *  init inode and write to disk
	 */
	DPRINT(2, "new file %llud.%ld ino %ld\n", qid.path, qid.vers, m - ic->map);
	b = ialloc(ic, m - ic->map);
	b->inode.inuse = m->inuse = 1;
	b->inode.qid = qid;
	b->inode.length = 0x7fffffffffffffffLL;
	m->qid = qid;
	b->inode.ptr.bno = Notabno;
	iwrite(ic, b);
	return b;
}

/*
 *  read an inode into the cache
 *
 *  ASSUMPTION: the inode is valid
 */
Ibuf*
iread(Icache *ic, ulong ino)
{
	Ibuf *b;
	Imap *m;
	ulong bno;
	Bbuf *bb;
	Dinode *bi;

	/*
	 *  first see if we already have it in a cache entry
	 */
	m = &ic->map[ino];
	if(m->inuse && m->b){
		b = m->b;
		goto out;
	}

	/*
	 *  read it
	 */
	b = ialloc(ic, ino);
	bno = ic->nab + ino/ic->i2b;
	bb = bcread(ic, bno);
	if(bb == 0){
		ifree(ic, b);
		return 0;
	}
	bi = (Dinode*)bb->data;
	b->inode = bi->inode[ino % ic->i2b];

	/*
	 *  consistency check
	 */
	if(bi->nino!=ic->nino || bi->magic!=Imagic){
		fprint(2, "iread: inconsistent inode block\n");
		ifree(ic, b);
		return 0;
	}
out:
	b->inuse = 1;
	m->b = b;
	if(b->inode.inuse)
		lruref(&ic->mlru, m);
	lruref(&ic->blru, b);
	return b;
}

/*
 *  write an inode back to disk
 */
int
iwrite(Icache *ic, Ibuf *b)
{
	ulong bno;
	Bbuf *bb;
	Dinode *bi;

	bno = ic->nab + b->ino/ic->i2b;
	bb = bcread(ic, bno);
	if(bb == 0)
		return 0;
	bi = (Dinode*)bb->data;
	bi->inode[b->ino % ic->i2b] = b->inode;
	bcmark(ic, bb);
	lruref(&ic->mlru, &ic->map[b->ino]);
	lruref(&ic->blru, b);
	return 0;
}

/*
 *  Forget what we know about an inode without removing it
 *
 *	N.B: ordering of iwrite and dfree is important
 */
int
iupdate(Icache *ic, ulong ino, Qid qid)
{
	Ibuf *b;
	Imap *m;
	Dptr d;

	if(statson){
		cfsstat.nupdate++;
	}
	b = iread(ic, ino);
	if(b == 0)
		return -1;

	/*
	 *  update inode and map
	 */
	b->inode.qid = qid;
	b->inode.length = 0x7fffffffffffffffLL;	/* Set to maximum */
	m = &ic->map[ino];
	m->qid = qid;

	/*
	 *  the free is not done if the write fails!
	 *  this is important
	 */
	d = b->inode.ptr;
	b->inode.ptr.bno = Notabno;
	if(iwrite(ic, b) < 0)
		return -1;
	dfree(ic, &d);
	return 0;
}

/*
 *  remove an inode
 *
 *	N.B: ordering of iwrite and dfree is important
 */
int
iremove(Icache *ic, ulong ino)
{
	Ibuf *b;
	Imap *m;

	if(statson){
		cfsstat.ndelete++;
	}
	m = &ic->map[ino];

	/*
	 *  read in inode
	 */
	b = iread(ic, ino);
	if(b == 0)
		return -1;

	/*
	 *  mark it unused on disk
	 */
	b->inode.inuse = 0;
	if(iwrite(ic, b) < 0)
		return -1;

	/*
	 *  throw out it's data pages
	 */
	dfree(ic, &b->inode.ptr);

	/*
	 *  free the inode buffer
	 */
	ifree(ic, b);

	/*
	 *  make map entry least recently used
	 */
	lruderef(&ic->mlru, m);
	return 0;
}

/*
 *  increment our version number
 */
void
iinc(Icache *ic, Ibuf *b)
{
	b->inode.qid.vers++;
	ic->map[b->ino].qid = b->inode.qid;
	iwrite(ic, b);
}