From 3e50ff795448c8ac427b41d10dab7c22a0ca5fb7 Mon Sep 17 00:00:00 2001
From: forever-learner <2360561713@qq.com>
Date: Thu, 30 Jun 2022 10:58:28 +0800
Subject: [PATCH] version 2 of mmap

---
 linux/kernel/sys.c | 124 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 112 insertions(+), 12 deletions(-)

diff --git a/linux/kernel/sys.c b/linux/kernel/sys.c
index 3a7a7b0..8b4d8d1 100644
--- a/linux/kernel/sys.c
+++ b/linux/kernel/sys.c
@@ -463,7 +463,42 @@ int sys_umask(int mask)
 	return (old);
 }
 
+static int my_share(unsigned long address, struct task_struct * p)
+{
+	unsigned long from;
+	unsigned long to;
+	unsigned long from_page;
+	unsigned long to_page;
+	unsigned long phys_addr;
+
+	from_page = to_page = ((address>>20) & 0xffc);
+	from_page += ((current->start_code>>20) & 0xffc);
+	to_page += ((p->start_code>>20) & 0xffc);
+
+	from = *(unsigned long *) from_page;
+	from &= 0xfffff000;
+	from_page = from + ((address>>10) & 0xffc);
+	phys_addr = *(unsigned long *) from_page;
+	to = *(unsigned long *) to_page;
+	if (!(to & 1))
+		if (to = get_free_page())
+			*(unsigned long *) to_page = to | 7;
+		else
+			return 0;
+	to &= 0xfffff000;
+	to_page = to + ((address>>10) & 0xffc);
+	if (1 & *(unsigned long *) to_page)
+		return 0;
+	/* share them: write-protect */
+	*(unsigned long *) to_page = *(unsigned long *) from_page;
+	phys_addr -= LOW_MEM;
+	phys_addr >>= 12;
+	mem_map[phys_addr]++;
+	return 1;
+}
+
 // rememeber to sync when munmap exit manual 
+
 long sys_mmap(void * start,size_t len,...)// int prot,int flags,int fd,off_t off
 {
 	printk("start mmaping\n");
@@ -475,27 +510,37 @@ long sys_mmap(void * start,size_t len,...)// int prot,int flags,int fd,off_t off
 	int *ll=&len;printk("%d,%d,%d,%d,%d\n",*ll,*(ll+1),*(ll+2),*(ll+3),*(ll+4));
 	va_end(args);
 	printk("%d,%d,%d,%ld\n",prot,flags,fd,off); */
+	
 	int block;
 	size_t l=len;
 	struct buffer_head * bh;
 	char *temp,*p1,*p2;
 	void * buf=start;
 	int tempprot=0;
+	
 	//因为new.h和namei.c定义不一样，要修改
 	if(prot &PROT_READ) tempprot |=4;
 	if(prot &PROT_EXEC) tempprot |=1;
 	if(prot &PROT_WRITE) tempprot |=2;
-	//特殊量
-	if(!len ||  off<0 || (off%PAGE_SIZE)) return MAP_FAILED;
+
+	//特殊量len>0 off%4096==0 prot至少有read权限
+	if(len<=0 ||  off<0 || (off%PAGE_SIZE)) 
+	{
+		if(len<=0) 
+			printk("the len of the wanting bytes must be positive");
+		else
+			printk("offset must be the mul of 4096");
+		return MAP_FAILED;
+	}	
 	if(!(prot& PROT_READ)) return MAP_FAILED;
-	//permissions of the file
-	printk("end of permissions0\n");
+
+	//permissions of the file ,搬运函数namei.c::permissions
 	printk("fd: %d\n",fd);
 	struct m_inode *inode=current->filp[fd]->f_inode;
 	printk("end of permissions\n");
 	int mode = inode->i_mode;
 	if (inode->i_dev && !inode->i_nlinks)
-		{printk("end of permissions1\n");;return MAP_FAILED;}
+		{printk("end of permissions1\n");return MAP_FAILED;}
 	else if (current->euid==inode->i_uid)
 		mode >>= 6;
 	else if (current->egid==inode->i_gid)
@@ -507,6 +552,9 @@ long sys_mmap(void * start,size_t len,...)// int prot,int flags,int fd,off_t off
 	}
 	//end of permission check
 	printk("end of permissions\n");
+	
+	//设置用户空间的虚拟地址，初始为32MB处，这样写在brk增长至32MB时会有bug,我们忽略
+	//同时，当栈向下增长到一定程度时，也会和当前地址冲突，我们忽略
 	if(start<=current->brk || start>=current->start_stack-0x8000 || start==NULL) 
 	{
 		if(!current->mmap_tail)
@@ -514,24 +562,76 @@ long sys_mmap(void * start,size_t len,...)// int prot,int flags,int fd,off_t off
 		else
 			buf=current->mmap_tail->endaddr;
 	}
+	//申请mmap
 	struct mmap_struct *mmap=(struct mmap_struct *)malloc(sizeof(struct mmap_struct));
-	mmap->address=buf;mmap->size=len;
-	mmap->endaddr=buf+(len + 0xfff)&0xfffff000;
-	mmap->rw=prot;mmap->ps=flags;
+	mmap->address=buf;
+	mmap->size=len;
+	mmap->endaddr=(unsigned long)buf+(len + 0xfff)&0xfffff000;
+	mmap->rw=prot;
+	mmap->ps=flags;
 	mmap->next=NULL;
+	//加入current->mmap
 	if(!current->mmap) 
-		{current->mmap=current->mapp_tail=mapp;}
+		{current->mmap=current->mmap_tail=mmap;}
 	else 
-		current->mmap_tail->next=mapp;
+		current->mmap_tail->next=mmap;
 	printk("buf: %x\n",(unsigned long )buf);
 	
+	//分配物理页
+
+	unsigned long from;
+	unsigned long to;
+	unsigned long from_page;
+	unsigned long to_page;
+	unsigned long phys_addr;
+	unsigned long tpage;
+	unsigned long address=mmap->address;
+	while(address<mmap->endaddr)
+	{
+		from_page =  ((mmap->address>>20) & 0xffc);
+		from_page += ((current->start_code>>20) & 0xffc);//页目录
+		if(!(*(unsigned long *)from_page&1))  //页表项不存在，申请页面
+			if(!(tpage=get_free_page()))
+			{
+				printk("out of memory.\n");
+				return MAP_FAILED;
+			}
+			else
+				*(unsigned long *)from_page= tpage | 7;
+		from=*(unsigned long *)from_page;	//页表项
+		from &= 0xfffff000;
+		from_page = from + ((address>>10) & 0xffc);
+		if(!(*(unsigned long *)from_page & 1))	//物理页不存在
+			if(!(tpage=get_free_page()))
+			{
+				printk("out of memory.\n");
+				return MAP_FAILED;
+			}
+			else
+				*(unsigned long *)from_page= tpage | 7; 
+		*(unsigned long *)from_page &= (prot&PROT_WRITE); //分配读写权限
+		if(flags & MAP_SHARED)
+		{
+			struct task_struct ** p;
+
+			for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
+				if (!*p)
+					continue;
+				if (current == *p)
+					continue;
+				if(!my_share(address,*p))
+					printk("share failed at task:pid=%d",(*p)->pid);
+			}
+		}
+		address+=PAGE_SIZE;
+	}
+		
 	//read and put in 
 	if (!(block = inode->i_zone[0]))
 		return NULL;
 	if (!(bh = bread(inode->i_dev,block)))
 		return NULL;
 	temp = (char *) bh->b_data;
-	printk("end of mmap\n");
 	p1=temp;p2=buf;
 	while(l--)
 		put_fs_byte(*(p1++),p2++);
@@ -542,4 +642,4 @@ int sys_munmap()
 {
 
 	return -1;
-}
\ No newline at end of file
+}