लिनक्स/linux-0.01.tar/fs/namei.c
< लिनक्स | linux-0.01.tar
#include <linux/sched.h>
#include <linux/kernel.h>
#include <asm/segment.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <const.h>
#include <sys/stat.h>
#define ACC_MODE(x) ("\004\002\006\377"[(x)&O_ACCMODE])
/*
* comment out this line if you want names > NAME_LEN chars to be
* truncated. Else they will be disallowed.
*/
/* #define NO_TRUNCATE */
#define MAY_EXEC 1
#define MAY_WRITE 2
#define MAY_READ 4
/*
* permission()
*
* is used to check for read/write/execute permissions on a file.
* I don't know if we should look at just the euid or both euid and
* uid, but that should be easily changed.
*/
static int permission(struct m_inode * inode,int mask)
{
int mode = inode->i_mode;
/* special case: not even root can read/write a deleted file */
if (inode->i_dev && !inode->i_nlinks)
return 0;
if (!(current->uid && current->euid))
mode=0777;
else if (current->uid==inode->i_uid || current->euid==inode->i_uid)
mode >>= 6;
else if (current->gid==inode->i_gid || current->egid==inode->i_gid)
mode >>= 3;
return mode & mask & 0007;
}
/*
* ok, we cannot use strncmp, as the name is not in our data space.
* Thus we'll have to use match. No big problem. Match also makes
* some sanity tests.
*
* NOTE! unlike strncmp, match returns 1 for success, 0 for failure.
*/
static int match(int len,const char * name,struct dir_entry * de)
{
register int same __asm__("ax");
if (!de || !de->inode || len > NAME_LEN)
return 0;
if (len < NAME_LEN && de->name[len])
return 0;
__asm__("cld\n\t"
"fs ; repe ; cmpsb\n\t"
"setz %%al"
:"=a" (same)
:"0" (0),"S" ((long) name),"D" ((long) de->name),"c" (len)
:"cx","di","si");
return same;
}
/*
* find_entry()
*
* finds and entry in the specified directory with the wanted name. It
* returns the cache buffer in which the entry was found, and the entry
* itself (as a parameter - res_dir). It does NOT read the inode of the
* entry - you'll have to do that yourself if you want to.
*/
static struct buffer_head * find_entry(struct m_inode * dir,
const char * name, int namelen, struct dir_entry ** res_dir)
{
int entries;
int block,i;
struct buffer_head * bh;
struct dir_entry * de;
#ifdef NO_TRUNCATE
if (namelen > NAME_LEN)
return NULL;
#else
if (namelen > NAME_LEN)
namelen = NAME_LEN;
#endif
entries = dir->i_size / (sizeof (struct dir_entry));
*res_dir = NULL;
if (!namelen)
return NULL;
if (!(block = dir->i_zone[0]))
return NULL;
if (!(bh = bread(dir->i_dev,block)))
return NULL;
i = 0;
de = (struct dir_entry *) bh->b_data;
while (i < entries) {
if ((char *)de >= BLOCK_SIZE+bh->b_data) {
brelse(bh);
bh = NULL;
if (!(block = bmap(dir,i/DIR_ENTRIES_PER_BLOCK)) ||
!(bh = bread(dir->i_dev,block))) {
i += DIR_ENTRIES_PER_BLOCK;
continue;
}
de = (struct dir_entry *) bh->b_data;
}
if (match(namelen,name,de)) {
*res_dir = de;
return bh;
}
de++;
i++;
}
brelse(bh);
return NULL;
}
/*
* add_entry()
*
* adds a file entry to the specified directory, using the same
* semantics as find_entry(). It returns NULL if it failed.
*
* NOTE!! The inode part of 'de' is left at 0 - which means you
* may not sleep between calling this and putting something into
* the entry, as someone else might have used it while you slept.
*/
static struct buffer_head * add_entry(struct m_inode * dir,
const char * name, int namelen, struct dir_entry ** res_dir)
{
int block,i;
struct buffer_head * bh;
struct dir_entry * de;
*res_dir = NULL;
#ifdef NO_TRUNCATE
if (namelen > NAME_LEN)
return NULL;
#else
if (namelen > NAME_LEN)
namelen = NAME_LEN;
#endif
if (!namelen)
return NULL;
if (!(block = dir->i_zone[0]))
return NULL;
if (!(bh = bread(dir->i_dev,block)))
return NULL;
i = 0;
de = (struct dir_entry *) bh->b_data;
while (1) {
if ((char *)de >= BLOCK_SIZE+bh->b_data) {
brelse(bh);
bh = NULL;
block = create_block(dir,i/DIR_ENTRIES_PER_BLOCK);
if (!block)
return NULL;
if (!(bh = bread(dir->i_dev,block))) {
i += DIR_ENTRIES_PER_BLOCK;
continue;
}
de = (struct dir_entry *) bh->b_data;
}
if (i*sizeof(struct dir_entry) >= dir->i_size) {
de->inode=0;
dir->i_size = (i+1)*sizeof(struct dir_entry);
dir->i_dirt = 1;
dir->i_ctime = CURRENT_TIME;
}
if (!de->inode) {
dir->i_mtime = CURRENT_TIME;
for (i=0; i < NAME_LEN ; i++)
de->name[i]=(i<namelen)?get_fs_byte(name+i):0;
bh->b_dirt = 1;
*res_dir = de;
return bh;
}
de++;
i++;
}
brelse(bh);
return NULL;
}
/*
* get_dir()
*
* Getdir traverses the pathname until it hits the topmost directory.
* It returns NULL on failure.
*/
static struct m_inode * get_dir(const char * pathname)
{
char c;
const char * thisname;
struct m_inode * inode;
struct buffer_head * bh;
int namelen,inr,idev;
struct dir_entry * de;
if (!current->root || !current->root->i_count)
panic("No root inode");
if (!current->pwd || !current->pwd->i_count)
panic("No cwd inode");
if ((c=get_fs_byte(pathname))=='/') {
inode = current->root;
pathname++;
} else if (c)
inode = current->pwd;
else
return NULL; /* empty name is bad */
inode->i_count++;
while (1) {
thisname = pathname;
if (!S_ISDIR(inode->i_mode) || !permission(inode,MAY_EXEC)) {
iput(inode);
return NULL;
}
for(namelen=0;(c=get_fs_byte(pathname++))&&(c!='/');namelen++)
/* nothing */ ;
if (!c)
return inode;
if (!(bh = find_entry(inode,thisname,namelen,&de))) {
iput(inode);
return NULL;
}
inr = de->inode;
idev = inode->i_dev;
brelse(bh);
iput(inode);
if (!(inode = iget(idev,inr)))
return NULL;
}
}
/*
* dir_namei()
*
* dir_namei() returns the inode of the directory of the
* specified name, and the name within that directory.
*/
static struct m_inode * dir_namei(const char * pathname,
int * namelen, const char ** name)
{
char c;
const char * basename;
struct m_inode * dir;
if (!(dir = get_dir(pathname)))
return NULL;
basename = pathname;
while (c=get_fs_byte(pathname++))
if (c=='/')
basename=pathname;
*namelen = pathname-basename-1;
*name = basename;
return dir;
}
/*
* namei()
*
* is used by most simple commands to get the inode of a specified name.
* Open, link etc use their own routines, but this is enough for things
* like 'chmod' etc.
*/
struct m_inode * namei(const char * pathname)
{
const char * basename;
int inr,dev,namelen;
struct m_inode * dir;
struct buffer_head * bh;
struct dir_entry * de;
if (!(dir = dir_namei(pathname,&namelen,&basename)))
return NULL;
if (!namelen) /* special case: '/usr/' etc */
return dir;
bh = find_entry(dir,basename,namelen,&de);
if (!bh) {
iput(dir);
return NULL;
}
inr = de->inode;
dev = dir->i_dev;
brelse(bh);
iput(dir);
dir=iget(dev,inr);
if (dir) {
dir->i_atime=CURRENT_TIME;
dir->i_dirt=1;
}
return dir;
}
/*
* open_namei()
*
* namei for open - this is in fact almost the whole open-routine.
*/
int open_namei(const char * pathname, int flag, int mode,
struct m_inode ** res_inode)
{
const char * basename;
int inr,dev,namelen;
struct m_inode * dir, *inode;
struct buffer_head * bh;
struct dir_entry * de;
if ((flag & O_TRUNC) && !(flag & O_ACCMODE))
flag |= O_WRONLY;
mode &= 0777 & ~current->umask;
mode |= I_REGULAR;
if (!(dir = dir_namei(pathname,&namelen,&basename)))
return -ENOENT;
if (!namelen) { /* special case: '/usr/' etc */
if (!(flag & (O_ACCMODE|O_CREAT|O_TRUNC))) {
*res_inode=dir;
return 0;
}
iput(dir);
return -EISDIR;
}
bh = find_entry(dir,basename,namelen,&de);
if (!bh) {
if (!(flag & O_CREAT)) {
iput(dir);
return -ENOENT;
}
if (!permission(dir,MAY_WRITE)) {
iput(dir);
return -EACCES;
}
inode = new_inode(dir->i_dev);
if (!inode) {
iput(dir);
return -ENOSPC;
}
inode->i_mode = mode;
inode->i_dirt = 1;
bh = add_entry(dir,basename,namelen,&de);
if (!bh) {
inode->i_nlinks--;
iput(inode);
iput(dir);
return -ENOSPC;
}
de->inode = inode->i_num;
bh->b_dirt = 1;
brelse(bh);
iput(dir);
*res_inode = inode;
return 0;
}
inr = de->inode;
dev = dir->i_dev;
brelse(bh);
iput(dir);
if (flag & O_EXCL)
return -EEXIST;
if (!(inode=iget(dev,inr)))
return -EACCES;
if ((S_ISDIR(inode->i_mode) && (flag & O_ACCMODE)) ||
permission(inode,ACC_MODE(flag))!=ACC_MODE(flag)) {
iput(inode);
return -EPERM;
}
inode->i_atime = CURRENT_TIME;
if (flag & O_TRUNC)
truncate(inode);
*res_inode = inode;
return 0;
}
int sys_mkdir(const char * pathname, int mode)
{
const char * basename;
int namelen;
struct m_inode * dir, * inode;
struct buffer_head * bh, *dir_block;
struct dir_entry * de;
if (current->euid && current->uid)
return -EPERM;
if (!(dir = dir_namei(pathname,&namelen,&basename)))
return -ENOENT;
if (!namelen) {
iput(dir);
return -ENOENT;
}
if (!permission(dir,MAY_WRITE)) {
iput(dir);
return -EPERM;
}
bh = find_entry(dir,basename,namelen,&de);
if (bh) {
brelse(bh);
iput(dir);
return -EEXIST;
}
inode = new_inode(dir->i_dev);
if (!inode) {
iput(dir);
return -ENOSPC;
}
inode->i_size = 32;
inode->i_dirt = 1;
inode->i_mtime = inode->i_atime = CURRENT_TIME;
if (!(inode->i_zone[0]=new_block(inode->i_dev))) {
iput(dir);
inode->i_nlinks--;
iput(inode);
return -ENOSPC;
}
inode->i_dirt = 1;
if (!(dir_block=bread(inode->i_dev,inode->i_zone[0]))) {
iput(dir);
free_block(inode->i_dev,inode->i_zone[0]);
inode->i_nlinks--;
iput(inode);
return -ERROR;
}
de = (struct dir_entry *) dir_block->b_data;
de->inode=inode->i_num;
strcpy(de->name,".");
de++;
de->inode = dir->i_num;
strcpy(de->name,"..");
inode->i_nlinks = 2;
dir_block->b_dirt = 1;
brelse(dir_block);
inode->i_mode = I_DIRECTORY | (mode & 0777 & ~current->umask);
inode->i_dirt = 1;
bh = add_entry(dir,basename,namelen,&de);
if (!bh) {
iput(dir);
free_block(inode->i_dev,inode->i_zone[0]);
inode->i_nlinks=0;
iput(inode);
return -ENOSPC;
}
de->inode = inode->i_num;
bh->b_dirt = 1;
dir->i_nlinks++;
dir->i_dirt = 1;
iput(dir);
iput(inode);
brelse(bh);
return 0;
}
/*
* routine to check that the specified directory is empty (for rmdir)
*/
static int empty_dir(struct m_inode * inode)
{
int nr,block;
int len;
struct buffer_head * bh;
struct dir_entry * de;
len = inode->i_size / sizeof (struct dir_entry);
if (len<2 || !inode->i_zone[0] ||
!(bh=bread(inode->i_dev,inode->i_zone[0]))) {
printk("warning - bad directory on dev %04x\n",inode->i_dev);
return 0;
}
de = (struct dir_entry *) bh->b_data;
if (de[0].inode != inode->i_num || !de[1].inode ||
strcmp(".",de[0].name) || strcmp("..",de[1].name)) {
printk("warning - bad directory on dev %04x\n",inode->i_dev);
return 0;
}
nr = 2;
de += 2;
while (nr<len) {
if ((void *) de >= (void *) (bh->b_data+BLOCK_SIZE)) {
brelse(bh);
block=bmap(inode,nr/DIR_ENTRIES_PER_BLOCK);
if (!block) {
nr += DIR_ENTRIES_PER_BLOCK;
continue;
}
if (!(bh=bread(inode->i_dev,block)))
return 0;
de = (struct dir_entry *) bh->b_data;
}
if (de->inode) {
brelse(bh);
return 0;
}
de++;
nr++;
}
brelse(bh);
return 1;
}
int sys_rmdir(const char * name)
{
const char * basename;
int namelen;
struct m_inode * dir, * inode;
struct buffer_head * bh;
struct dir_entry * de;
if (current->euid && current->uid)
return -EPERM;
if (!(dir = dir_namei(name,&namelen,&basename)))
return -ENOENT;
if (!namelen) {
iput(dir);
return -ENOENT;
}
bh = find_entry(dir,basename,namelen,&de);
if (!bh) {
iput(dir);
return -ENOENT;
}
if (!permission(dir,MAY_WRITE)) {
iput(dir);
brelse(bh);
return -EPERM;
}
if (!(inode = iget(dir->i_dev, de->inode))) {
iput(dir);
brelse(bh);
return -EPERM;
}
if (inode == dir) { /* we may not delete ".", but "../dir" is ok */
iput(inode);
iput(dir);
brelse(bh);
return -EPERM;
}
if (!S_ISDIR(inode->i_mode)) {
iput(inode);
iput(dir);
brelse(bh);
return -ENOTDIR;
}
if (!empty_dir(inode)) {
iput(inode);
iput(dir);
brelse(bh);
return -ENOTEMPTY;
}
if (inode->i_nlinks != 2)
printk("empty directory has nlink!=2 (%d)",inode->i_nlinks);
de->inode = 0;
bh->b_dirt = 1;
brelse(bh);
inode->i_nlinks=0;
inode->i_dirt=1;
dir->i_nlinks--;
dir->i_ctime = dir->i_mtime = CURRENT_TIME;
dir->i_dirt=1;
iput(dir);
iput(inode);
return 0;
}
int sys_unlink(const char * name)
{
const char * basename;
int namelen;
struct m_inode * dir, * inode;
struct buffer_head * bh;
struct dir_entry * de;
if (!(dir = dir_namei(name,&namelen,&basename)))
return -ENOENT;
if (!namelen) {
iput(dir);
return -ENOENT;
}
if (!permission(dir,MAY_WRITE)) {
iput(dir);
return -EPERM;
}
bh = find_entry(dir,basename,namelen,&de);
if (!bh) {
iput(dir);
return -ENOENT;
}
inode = iget(dir->i_dev, de->inode);
if (!inode) {
printk("iget failed in delete (%04x:%d)",dir->i_dev,de->inode);
iput(dir);
brelse(bh);
return -ENOENT;
}
if (!S_ISREG(inode->i_mode)) {
iput(inode);
iput(dir);
brelse(bh);
return -EPERM;
}
if (!inode->i_nlinks) {
printk("Deleting nonexistent file (%04x:%d), %d\n",
inode->i_dev,inode->i_num,inode->i_nlinks);
inode->i_nlinks=1;
}
de->inode = 0;
bh->b_dirt = 1;
brelse(bh);
inode->i_nlinks--;
inode->i_dirt = 1;
inode->i_ctime = CURRENT_TIME;
iput(inode);
iput(dir);
return 0;
}
int sys_link(const char * oldname, const char * newname)
{
struct dir_entry * de;
struct m_inode * oldinode, * dir;
struct buffer_head * bh;
const char * basename;
int namelen;
oldinode=namei(oldname);
if (!oldinode)
return -ENOENT;
if (!S_ISREG(oldinode->i_mode)) {
iput(oldinode);
return -EPERM;
}
dir = dir_namei(newname,&namelen,&basename);
if (!dir) {
iput(oldinode);
return -EACCES;
}
if (!namelen) {
iput(oldinode);
iput(dir);
return -EPERM;
}
if (dir->i_dev != oldinode->i_dev) {
iput(dir);
iput(oldinode);
return -EXDEV;
}
if (!permission(dir,MAY_WRITE)) {
iput(dir);
iput(oldinode);
return -EACCES;
}
bh = find_entry(dir,basename,namelen,&de);
if (bh) {
brelse(bh);
iput(dir);
iput(oldinode);
return -EEXIST;
}
bh = add_entry(dir,basename,namelen,&de);
if (!bh) {
iput(dir);
iput(oldinode);
return -ENOSPC;
}
de->inode = oldinode->i_num;
bh->b_dirt = 1;
brelse(bh);
iput(dir);
oldinode->i_nlinks++;
oldinode->i_ctime = CURRENT_TIME;
oldinode->i_dirt = 1;
iput(oldinode);
return 0;
}