file.c

这是著名的jffs2嵌入式日志文件系统的源代码

			pg_buf += holeend - offset;
			offset = holeend;
			frag = frag->next;
			continue;
		} else {
			__u32 readlen;
			readlen = min(frag->size, end - offset);
			D1(printk(KERN_DEBUG "Reading %d-%d from node at 0x%x\n", frag->ofs, frag->ofs+readlen, frag->node->raw->flash_offset & ~3));
			ret = jffs2_read_dnode(c, frag->node, pg_buf, frag->ofs - frag->node->ofs, readlen);
			D2(printk(KERN_DEBUG "node read done\n"));
			if (ret) {
				D1(printk(KERN_DEBUG"jffs2_readpage error %d\n",ret));
				memset(pg_buf, 0, frag->size);
				ClearPageUptodate(pg);
				SetPageError(pg);
				kunmap(pg);
				return ret;
			}
		}
		pg_buf += frag->size;
		offset += frag->size;
		frag = frag->next;
		D2(printk(KERN_DEBUG "node read was OK. Looping\n"));
	}
	D2(printk(KERN_DEBUG "readpage finishing\n"));
	SetPageUptodate(pg);
	ClearPageError(pg);

	flush_dcache_page(pg);

	kunmap(pg);
	D1(printk(KERN_DEBUG "readpage finished\n"));
	return 0;
}

int jffs2_do_readpage_unlock(struct inode *inode, struct page *pg)
{
	int ret = jffs2_do_readpage_nolock(inode, pg);
	UnlockPage(pg);
	return ret;
}


int jffs2_readpage (struct file *filp, struct page *pg)
{
	struct jffs2_inode_info *f = JFFS2_INODE_INFO(filp->f_dentry->d_inode);
	int ret;
	
	down(&f->sem);
	ret = jffs2_do_readpage_unlock(filp->f_dentry->d_inode, pg);
	up(&f->sem);
	return ret;
}

int jffs2_prepare_write (struct file *filp, struct page *pg, unsigned start, unsigned end)
{
	struct inode *inode = filp->f_dentry->d_inode;
	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
	__u32 pageofs = pg->index << PAGE_CACHE_SHIFT;
	int ret = 0;

	down(&f->sem);
	D1(printk(KERN_DEBUG "jffs2_prepare_write() nrpages %ld\n", inode->i_mapping->nrpages));

	if (pageofs > inode->i_size) {
		/* Make new hole frag from old EOF to new page */
		struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
		struct jffs2_raw_inode ri;
		struct jffs2_full_dnode *fn;
		__u32 phys_ofs, alloc_len;
		
		D1(printk(KERN_DEBUG "Writing new hole frag 0x%x-0x%x between current EOF and new page\n",
			  (unsigned int)inode->i_size, pageofs));

		ret = jffs2_reserve_space(c, sizeof(ri), &phys_ofs, &alloc_len, ALLOC_NORMAL);
		if (ret) {
			up(&f->sem);
			return ret;
		}
		memset(&ri, 0, sizeof(ri));

		ri.magic = JFFS2_MAGIC_BITMASK;
		ri.nodetype = JFFS2_NODETYPE_INODE;
		ri.totlen = sizeof(ri);
		ri.hdr_crc = crc32(0, &ri, sizeof(struct jffs2_unknown_node)-4);

		ri.ino = f->inocache->ino;
		ri.version = ++f->highest_version;
		ri.mode = inode->i_mode;
		ri.uid = inode->i_uid;
		ri.gid = inode->i_gid;
		ri.isize = max((__u32)inode->i_size, pageofs);
		ri.atime = ri.ctime = ri.mtime = CURRENT_TIME;
		ri.offset = inode->i_size;
		ri.dsize = pageofs - inode->i_size;
		ri.csize = 0;
		ri.compr = JFFS2_COMPR_ZERO;
		ri.node_crc = crc32(0, &ri, sizeof(ri)-8);
		ri.data_crc = 0;
		
		fn = jffs2_write_dnode(inode, &ri, NULL, 0, phys_ofs, NULL);
		jffs2_complete_reservation(c);
		if (IS_ERR(fn)) {
			ret = PTR_ERR(fn);
			up(&f->sem);
			return ret;
		}
		ret = jffs2_add_full_dnode_to_inode(c, f, fn);
		if (f->metadata) {
			jffs2_mark_node_obsolete(c, f->metadata->raw);
			jffs2_free_full_dnode(f->metadata);
			f->metadata = NULL;
		}
		if (ret) {
			D1(printk(KERN_DEBUG "Eep. add_full_dnode_to_inode() failed in prepare_write, returned %d\n", ret));
			jffs2_mark_node_obsolete(c, fn->raw);
			jffs2_free_full_dnode(fn);
			up(&f->sem);
			return ret;
		}
		inode->i_size = pageofs;
	}
	

	/* Read in the page if it wasn't already present */
	if (!Page_Uptodate(pg) && (start || end < PAGE_SIZE))
		ret = jffs2_do_readpage_nolock(inode, pg);
	D1(printk(KERN_DEBUG "end prepare_write(). nrpages %ld\n", inode->i_mapping->nrpages));
	up(&f->sem);
	return ret;
}

int jffs2_commit_write (struct file *filp, struct page *pg, unsigned start, unsigned end)
{
	/* Actually commit the write from the page cache page we're looking at.
	 * For now, we write the full page out each time. It sucks, but it's simple
	 */
	struct inode *inode = filp->f_dentry->d_inode;
	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
	struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
	__u32 newsize = max_t(__u32, filp->f_dentry->d_inode->i_size, (pg->index << PAGE_CACHE_SHIFT) + end);
	__u32 file_ofs = (pg->index << PAGE_CACHE_SHIFT);
	__u32 writelen = min((__u32)PAGE_CACHE_SIZE, newsize - file_ofs);
	struct jffs2_raw_inode *ri;
	int ret = 0;
	ssize_t writtenlen = 0;

	D1(printk(KERN_DEBUG "jffs2_commit_write(): ino #%lu, page at 0x%lx, range %d-%d, nrpages %ld\n", inode->i_ino, pg->index << PAGE_CACHE_SHIFT, start, end, filp->f_dentry->d_inode->i_mapping->nrpages));

	ri = jffs2_alloc_raw_inode();
	if (!ri)
		return -ENOMEM;

	while(writelen) {
		struct jffs2_full_dnode *fn;
		unsigned char *comprbuf = NULL;
		unsigned char comprtype = JFFS2_COMPR_NONE;
		__u32 phys_ofs, alloclen;
		__u32 datalen, cdatalen;

		D2(printk(KERN_DEBUG "jffs2_commit_write() loop: 0x%x to write to 0x%x\n", writelen, file_ofs));

		ret = jffs2_reserve_space(c, sizeof(*ri) + JFFS2_MIN_DATA_LEN, &phys_ofs, &alloclen, ALLOC_NORMAL);
		if (ret) {
			SetPageError(pg);
			D1(printk(KERN_DEBUG "jffs2_reserve_space returned %d\n", ret));
			break;
		}
		down(&f->sem);
		datalen = writelen;
		cdatalen = min(alloclen - sizeof(*ri), writelen);

		comprbuf = kmalloc(cdatalen, GFP_KERNEL);
		if (comprbuf) {
			comprtype = jffs2_compress(page_address(pg)+ (file_ofs & (PAGE_CACHE_SIZE-1)), comprbuf, &datalen, &cdatalen);
		}
		if (comprtype == JFFS2_COMPR_NONE) {
			/* Either compression failed, or the allocation of comprbuf failed */
			if (comprbuf)
				kfree(comprbuf);
			comprbuf = page_address(pg) + (file_ofs & (PAGE_CACHE_SIZE -1));
			datalen = cdatalen;
		}
		/* Now comprbuf points to the data to be written, be it compressed or not.
		   comprtype holds the compression type, and comprtype == JFFS2_COMPR_NONE means
		   that the comprbuf doesn't need to be kfree()d. 
		*/

		ri->magic = JFFS2_MAGIC_BITMASK;
		ri->nodetype = JFFS2_NODETYPE_INODE;
		ri->totlen = sizeof(*ri) + cdatalen;
		ri->hdr_crc = crc32(0, ri, sizeof(struct jffs2_unknown_node)-4);

		ri->ino = inode->i_ino;
		ri->version = ++f->highest_version;
		ri->mode = inode->i_mode;
		ri->uid = inode->i_uid;
		ri->gid = inode->i_gid;
		ri->isize = max((__u32)inode->i_size, file_ofs + datalen);
		ri->atime = ri->ctime = ri->mtime = CURRENT_TIME;
		ri->offset = file_ofs;
		ri->csize = cdatalen;
		ri->dsize = datalen;
		ri->compr = comprtype;
		ri->node_crc = crc32(0, ri, sizeof(*ri)-8);
		ri->data_crc = crc32(0, comprbuf, cdatalen);

		fn = jffs2_write_dnode(inode, ri, comprbuf, cdatalen, phys_ofs, NULL);

		jffs2_complete_reservation(c);

		if (comprtype != JFFS2_COMPR_NONE)
			kfree(comprbuf);

		if (IS_ERR(fn)) {
			ret = PTR_ERR(fn);
			up(&f->sem);
			SetPageError(pg);
			break;
		}
		ret = jffs2_add_full_dnode_to_inode(c, f, fn);
		if (f->metadata) {
			jffs2_mark_node_obsolete(c, f->metadata->raw);
			jffs2_free_full_dnode(f->metadata);
			f->metadata = NULL;
		}
		up(&f->sem);
		if (ret) {
			/* Eep */
			D1(printk(KERN_DEBUG "Eep. add_full_dnode_to_inode() failed in commit_write, returned %d\n", ret));
			jffs2_mark_node_obsolete(c, fn->raw);
			jffs2_free_full_dnode(fn);
			SetPageError(pg);
			break;
		}
		inode->i_size = ri->isize;
		inode->i_blocks = (inode->i_size + 511) >> 9;
		inode->i_ctime = inode->i_mtime = ri->ctime;
		if (!datalen) {
			printk(KERN_WARNING "Eep. We didn't actually write any bloody data\n");
			ret = -EIO;
			SetPageError(pg);
			break;
		}
		D1(printk(KERN_DEBUG "increasing writtenlen by %d\n", datalen));
		writtenlen += datalen;
		file_ofs += datalen;
		writelen -= datalen;
	}

	jffs2_free_raw_inode(ri);

	if (writtenlen < end) {
		/* generic_file_write has written more to the page cache than we've
		   actually written to the medium. Mark the page !Uptodate so that 
		   it gets reread */
		D1(printk(KERN_DEBUG "jffs2_commit_write(): Not all bytes written. Marking page !uptodate\n"));
		SetPageError(pg);
		ClearPageUptodate(pg);
	}
	if (writtenlen <= start) {
		/* We didn't even get to the start of the affected part */
		ret = ret?ret:-ENOSPC;
		D1(printk(KERN_DEBUG "jffs2_commit_write(): Only %x bytes written to page. start (%x) not reached, returning %d\n", writtenlen, start, ret));
	}
	writtenlen = min(end-start, writtenlen-start);

	D1(printk(KERN_DEBUG "jffs2_commit_write() returning %d. nrpages is %ld\n",writtenlen?writtenlen:ret, inode->i_mapping->nrpages));
	return writtenlen?writtenlen:ret;
}