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minix3/fs/mfs/path.c

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/* This file contains the procedures that look up path names in the directory
* system and determine the inode number that goes with a given path name.
*
* The entry points into this file are
* eat_path: the 'main' routine of the path-to-inode conversion mechanism
* last_dir: find the final directory on a given path
* advance: parse one component of a path name
* search_dir: search a directory for a string and return its inode number
*
*/
#include "fs.h"
#include "assert.h"
#include <string.h>
#include <minix/endpoint.h>
#include <sys/stat.h>
#include <sys/types.h>
#include "buf.h"
#include "inode.h"
#include "super.h"
#include <minix/vfsif.h>
#include <minix/libminixfs.h>
char dot1[2] = "."; /* used for search_dir to bypass the access */
char dot2[3] = ".."; /* permissions for . and .. */
static char *get_name(char *name, char string[MFS_NAME_MAX+1]);
static int ltraverse(struct inode *rip, char *suffix);
static int parse_path(ino_t dir_ino, ino_t root_ino, int flags, struct
inode **res_inop, size_t *offsetp, int *symlinkp);
/*===========================================================================*
* fs_lookup *
*===========================================================================*/
int fs_lookup()
{
cp_grant_id_t grant;
int r, r1, flags, symlinks;
unsigned int len;
size_t offset = 0, path_size;
ino_t dir_ino, root_ino;
struct inode *rip;
grant = fs_m_in.m_vfs_fs_lookup.grant_path;
path_size = fs_m_in.m_vfs_fs_lookup.path_size; /* Size of the buffer */
len = fs_m_in.m_vfs_fs_lookup.path_len; /* including terminating nul */
dir_ino = fs_m_in.m_vfs_fs_lookup.dir_ino;
root_ino = fs_m_in.m_vfs_fs_lookup.root_ino;
flags = fs_m_in.m_vfs_fs_lookup.flags;
/* Check length. */
if(len > sizeof(user_path)) return(E2BIG); /* too big for buffer */
if(len == 0) return(EINVAL); /* too small */
/* Copy the pathname and set up caller's user and group id */
r = sys_safecopyfrom(VFS_PROC_NR, grant, /*offset*/ (vir_bytes) 0,
(vir_bytes) user_path, (size_t) len);
if(r != OK) return(r);
/* Verify this is a null-terminated path. */
if(user_path[len - 1] != '\0') return(EINVAL);
memset(&credentials, 0, sizeof(credentials));
if(!(flags & PATH_GET_UCRED)) { /* Do we have to copy uid/gid credentials? */
caller_uid = fs_m_in.m_vfs_fs_lookup.uid;
caller_gid = fs_m_in.m_vfs_fs_lookup.gid;
} else {
if((r=fs_lookup_credentials(&credentials,
&caller_uid, &caller_gid,
fs_m_in.m_vfs_fs_lookup.grant_ucred,
fs_m_in.m_vfs_fs_lookup.ucred_size)) != OK)
return r;
}
/* Lookup inode */
rip = NULL;
r = parse_path(dir_ino, root_ino, flags, &rip, &offset, &symlinks);
if(symlinks != 0 && (r == ELEAVEMOUNT || r == EENTERMOUNT || r == ESYMLINK)){
len = strlen(user_path)+1;
if(len > path_size) return(ENAMETOOLONG);
r1 = sys_safecopyto(VFS_PROC_NR, grant, (vir_bytes) 0,
(vir_bytes) user_path, (size_t) len);
if(r1 != OK) return(r1);
}
if(r == ELEAVEMOUNT || r == ESYMLINK) {
/* Report offset and the error */
fs_m_out.m_fs_vfs_lookup.offset = offset;
fs_m_out.m_fs_vfs_lookup.symloop = symlinks;
return(r);
}
if (r != OK && r != EENTERMOUNT) return(r);
fs_m_out.m_fs_vfs_lookup.inode = rip->i_num;
fs_m_out.m_fs_vfs_lookup.mode = rip->i_mode;
fs_m_out.m_fs_vfs_lookup.file_size = rip->i_size;
fs_m_out.m_fs_vfs_lookup.symloop = symlinks;
fs_m_out.m_fs_vfs_lookup.uid = rip->i_uid;
fs_m_out.m_fs_vfs_lookup.gid = rip->i_gid;
/* This is only valid for block and character specials. But it doesn't
* cause any harm to always set the device field. */
fs_m_out.m_fs_vfs_lookup.device = (dev_t) rip->i_zone[0];
if(r == EENTERMOUNT) {
fs_m_out.m_fs_vfs_lookup.offset = offset;
put_inode(rip); /* Only return a reference to the final object */
}
return(r);
}
/*===========================================================================*
* parse_path *
*===========================================================================*/
static int parse_path(
ino_t dir_ino,
ino_t root_ino,
int flags,
struct inode **res_inop,
size_t *offsetp,
int *symlinkp
) {
/* Parse the path in user_path, starting at dir_ino. If the path is the empty
* string, just return dir_ino. It is upto the caller to treat an empty
* path in a special way. Otherwise, if the path consists of just one or
* more slash ('/') characters, the path is replaced with ".". Otherwise,
* just look up the first (or only) component in path after skipping any
* leading slashes.
*/
int r, leaving_mount;
struct inode *rip, *dir_ip;
char *cp, *next_cp; /* component and next component */
char component[MFS_NAME_MAX+1];
/* Start parsing path at the first component in user_path */
cp = user_path;
/* No symlinks encountered yet */
*symlinkp = 0;
/* Find starting inode inode according to the request message */
if((rip = find_inode(fs_dev, dir_ino)) == NULL)
return(ENOENT);
/* If dir has been removed return ENOENT. */
if (rip->i_nlinks == NO_LINK) return(ENOENT);
dup_inode(rip);
/* If the given start inode is a mountpoint, we must be here because the file
* system mounted on top returned an ELEAVEMOUNT error. In this case, we must
* only accept ".." as the first path component.
*/
leaving_mount = rip->i_mountpoint; /* True iff rip is a mountpoint */
/* Scan the path component by component. */
while (TRUE) {
if(cp[0] == '\0') {
/* We're done; either the path was empty or we've parsed all
components of the path */
*res_inop = rip;
*offsetp += cp - user_path;
/* Return EENTERMOUNT if we are at a mount point */
if (rip->i_mountpoint) return(EENTERMOUNT);
return(OK);
}
while(cp[0] == '/') cp++;
next_cp = get_name(cp, component);
/* Special code for '..'. A process is not allowed to leave a chrooted
* environment. A lookup of '..' at the root of a mounted filesystem
* has to return ELEAVEMOUNT. In both cases, the caller needs search
* permission for the current inode, as it is used as directory.
*/
if(strcmp(component, "..") == 0) {
/* 'rip' is now accessed as directory */
if ((r = forbidden(rip, X_BIT)) != OK) {
put_inode(rip);
return(r);
}
if (rip->i_num == root_ino) {
cp = next_cp;
continue; /* Ignore the '..' at a process' root
and move on to the next component */
}
if (rip->i_num == ROOT_INODE && !rip->i_sp->s_is_root) {
/* Climbing up to parent FS */
put_inode(rip);
*offsetp += cp - user_path;
return(ELEAVEMOUNT);
}
}
/* Only check for a mount point if we are not coming from one. */
if (!leaving_mount && rip->i_mountpoint) {
/* Going to enter a child FS */
*res_inop = rip;
*offsetp += cp - user_path;
return(EENTERMOUNT);
}
/* There is more path. Keep parsing.
* If we're leaving a mountpoint, skip directory permission checks.
*/
dir_ip = rip;
rip = advance(dir_ip, leaving_mount ? dot2 : component, CHK_PERM);
if(err_code == ELEAVEMOUNT || err_code == EENTERMOUNT)
err_code = OK;
if (err_code != OK) {
put_inode(dir_ip);
return(err_code);
}
leaving_mount = 0;
/* The call to advance() succeeded. Fetch next component. */
if (S_ISLNK(rip->i_mode)) {
if (next_cp[0] == '\0' && (flags & PATH_RET_SYMLINK)) {
put_inode(dir_ip);
*res_inop = rip;
*offsetp += next_cp - user_path;
return(OK);
}
/* Extract path name from the symlink file */
r = ltraverse(rip, next_cp);
next_cp = user_path;
*offsetp = 0;
/* Symloop limit reached? */
if (++(*symlinkp) > _POSIX_SYMLOOP_MAX)
r = ELOOP;
if (r != OK) {
put_inode(dir_ip);
put_inode(rip);
return(r);
}
if (next_cp[0] == '/') {
put_inode(dir_ip);
put_inode(rip);
return(ESYMLINK);
}
put_inode(rip);
dup_inode(dir_ip);
rip = dir_ip;
}
put_inode(dir_ip);
cp = next_cp; /* Process subsequent component in next round */
}
}
/*===========================================================================*
* ltraverse *
*===========================================================================*/
static int ltraverse(rip, suffix)
register struct inode *rip; /* symbolic link */
char *suffix; /* current remaining path. Has to point in the
* user_path buffer
*/
{
/* Traverse a symbolic link. Copy the link text from the inode and insert
* the text into the path. Return error code or report success. Base
* directory has to be determined according to the first character of the
* new pathname.
*/
size_t llen; /* length of link */
size_t slen; /* length of suffix */
struct buf *bp; /* buffer containing link text */
char *sp; /* start of link text */
if(!(bp = get_block_map(rip, 0)))
return(EIO);
llen = (size_t) rip->i_size;
sp = b_data(bp);
slen = strlen(suffix);
/* The path we're parsing looks like this:
* /already/processed/path/<link> or
* /already/processed/path/<link>/not/yet/processed/path
* After expanding the <link>, the path will look like
* <expandedlink> or
* <expandedlink>/not/yet/processed
* In both cases user_path must have enough room to hold <expandedlink>.
* However, in the latter case we have to move /not/yet/processed to the
* right place first, before we expand <link>. When strlen(<expandedlink>) is
* smaller than strlen(/already/processes/path), we move the suffix to the
* left. Is strlen(<expandedlink>) greater then we move it to the right. Else
* we do nothing.
*/
if (slen > 0) { /* Do we have path after the link? */
/* For simplicity we require that suffix starts with a slash */
if (suffix[0] != '/') {
panic("ltraverse: suffix does not start with a slash");
}
/* To be able to expand the <link>, we have to move the 'suffix'
* to the right place.
*/
if (slen + llen + 1 > sizeof(user_path))
return(ENAMETOOLONG);/* <expandedlink>+suffix+\0 does not fit*/
if ((unsigned) (suffix-user_path) != llen) {
/* Move suffix left or right */
memmove(&user_path[llen], suffix, slen+1);
}
} else {
if (llen + 1 > sizeof(user_path))
return(ENAMETOOLONG); /* <expandedlink> + \0 does not fix */
/* Set terminating nul */
user_path[llen]= '\0';
}
/* Everything is set, now copy the expanded link to user_path */
memmove(user_path, sp, llen);
put_block(bp, DIRECTORY_BLOCK);
return(OK);
}
/*===========================================================================*
* advance *
*===========================================================================*/
struct inode *advance(dirp, string, chk_perm)
struct inode *dirp; /* inode for directory to be searched */
char string[MFS_NAME_MAX]; /* component name to look for */
int chk_perm; /* check permissions when string is looked up*/
{
/* Given a directory and a component of a path, look up the component in
* the directory, find the inode, open it, and return a pointer to its inode
* slot.
*/
ino_t numb;
struct inode *rip;
/* If 'string' is empty, return an error. */
if (string[0] == '\0') {
err_code = ENOENT;
return(NULL);
}
/* Check for NULL. */
if (dirp == NULL) return(NULL);
/* If 'string' is not present in the directory, signal error. */
if ( (err_code = search_dir(dirp, string, &numb, LOOK_UP, chk_perm)) != OK) {
return(NULL);
}
/* The component has been found in the directory. Get inode. */
if ( (rip = get_inode(dirp->i_dev, (int) numb)) == NULL) {
return(NULL);
}
/* The following test is for "mountpoint/.." where mountpoint is a
* mountpoint. ".." will refer to the root of the mounted filesystem,
* but has to become a reference to the parent of the 'mountpoint'
* directory.
*
* This case is recognized by the looked up name pointing to a
* root inode, and the directory in which it is held being a
* root inode, _and_ the name[1] being '.'. (This is a test for '..'
* and excludes '.'.)
*/
if (rip->i_num == ROOT_INODE) {
if (dirp->i_num == ROOT_INODE) {
if (string[1] == '.') {
if (!rip->i_sp->s_is_root) {
/* Climbing up mountpoint */
err_code = ELEAVEMOUNT;
}
}
}
}
/* See if the inode is mounted on. If so, switch to root directory of the
* mounted file system. The super_block provides the linkage between the
* inode mounted on and the root directory of the mounted file system.
*/
if (rip->i_mountpoint) {
/* Mountpoint encountered, report it */
err_code = EENTERMOUNT;
}
return(rip);
}
/*===========================================================================*
* get_name *
*===========================================================================*/
static char *get_name(path_name, string)
char *path_name; /* path name to parse */
char string[MFS_NAME_MAX+1]; /* component extracted from 'old_name' */
{
/* Given a pointer to a path name in fs space, 'path_name', copy the first
* component to 'string' (truncated if necessary, always nul terminated).
* A pointer to the string after the first component of the name as yet
* unparsed is returned. Roughly speaking,
* 'get_name' = 'path_name' - 'string'.
*
* This routine follows the standard convention that /usr/ast, /usr//ast,
* //usr///ast and /usr/ast/ are all equivalent.
*/
size_t len;
char *cp, *ep;
cp = path_name;
/* Skip leading slashes */
while (cp[0] == '/') cp++;
/* Find the end of the first component */
ep = cp;
while(ep[0] != '\0' && ep[0] != '/')
ep++;
len = (size_t) (ep - cp);
/* Truncate the amount to be copied if it exceeds MFS_NAME_MAX */
if (len > MFS_NAME_MAX) len = MFS_NAME_MAX;
/* Special case of the string at cp is empty */
if (len == 0)
strlcpy(string, ".", MFS_NAME_MAX + 1); /* Return "." */
else {
memcpy(string, cp, len);
string[len]= '\0';
}
return(ep);
}
/*===========================================================================*
* search_dir *
*===========================================================================*/
int search_dir(ldir_ptr, string, numb, flag, check_permissions)
register struct inode *ldir_ptr; /* ptr to inode for dir to search */
char string[MFS_NAME_MAX]; /* component to search for */
ino_t *numb; /* pointer to inode number */
int flag; /* LOOK_UP, ENTER, DELETE or IS_EMPTY */
int check_permissions; /* check permissions when flag is !IS_EMPTY */
{
/* This function searches the directory whose inode is pointed to by 'ldip':
* if (flag == ENTER) enter 'string' in the directory with inode # '*numb';
* if (flag == DELETE) delete 'string' from the directory;
* if (flag == LOOK_UP) search for 'string' and return inode # in 'numb';
* if (flag == IS_EMPTY) return OK if only . and .. in dir else ENOTEMPTY;
*
* if 'string' is dot1 or dot2, no access permissions are checked.
*/
register struct direct *dp = NULL;
register struct buf *bp = NULL;
int i, r, e_hit, t, match;
mode_t bits;
off_t pos;
unsigned new_slots, old_slots;
struct super_block *sp;
int extended = 0;
/* If 'ldir_ptr' is not a pointer to a dir inode, error. */
if ( (ldir_ptr->i_mode & I_TYPE) != I_DIRECTORY) {
return(ENOTDIR);
}
if((flag == DELETE || flag == ENTER) && ldir_ptr->i_sp->s_rd_only)
return EROFS;
r = OK;
if (flag != IS_EMPTY) {
bits = (flag == LOOK_UP ? X_BIT : W_BIT | X_BIT);
if (string == dot1 || string == dot2) {
if (flag != LOOK_UP) r = read_only(ldir_ptr);
/* only a writable device is required. */
} else if(check_permissions) {
r = forbidden(ldir_ptr, bits); /* check access permissions */
}
}
if (r != OK) return(r);
/* Step through the directory one block at a time. */
old_slots = (unsigned) (ldir_ptr->i_size/DIR_ENTRY_SIZE);
new_slots = 0;
e_hit = FALSE;
match = 0; /* set when a string match occurs */
pos = 0;
if (flag == ENTER && ldir_ptr->i_last_dpos < ldir_ptr->i_size) {
pos = ldir_ptr->i_last_dpos;
new_slots = (unsigned) (pos/DIR_ENTRY_SIZE);
}
for (; pos < ldir_ptr->i_size; pos += ldir_ptr->i_sp->s_block_size) {
assert(ldir_ptr->i_dev != NO_DEV);
/* Since directories don't have holes, 'b' cannot be NO_BLOCK. */
bp = get_block_map(ldir_ptr, pos);
assert(ldir_ptr->i_dev != NO_DEV);
assert(bp != NULL);
assert(lmfs_dev(bp) != NO_DEV);
/* Search a directory block. */
for (dp = &b_dir(bp)[0];
dp < &b_dir(bp)[NR_DIR_ENTRIES(ldir_ptr->i_sp->s_block_size)];
dp++) {
if (++new_slots > old_slots) { /* not found, but room left */
if (flag == ENTER) e_hit = TRUE;
break;
}
/* Match occurs if string found. */
if (flag != ENTER && dp->mfs_d_ino != NO_ENTRY) {
if (flag == IS_EMPTY) {
/* If this test succeeds, dir is not empty. */
if (strcmp(dp->mfs_d_name, "." ) != 0 &&
strcmp(dp->mfs_d_name, "..") != 0) match = 1;
} else {
if (strncmp(dp->mfs_d_name, string,
sizeof(dp->mfs_d_name)) == 0){
match = 1;
}
}
}
if (match) {
/* LOOK_UP or DELETE found what it wanted. */
r = OK;
if (flag == IS_EMPTY) r = ENOTEMPTY;
else if (flag == DELETE) {
/* Save d_ino for recovery. */
t = MFS_NAME_MAX - sizeof(ino_t);
*((ino_t *) &dp->mfs_d_name[t]) = dp->mfs_d_ino;
dp->mfs_d_ino = NO_ENTRY; /* erase entry */
MARKDIRTY(bp);
ldir_ptr->i_update |= CTIME | MTIME;
IN_MARKDIRTY(ldir_ptr);
if (pos < ldir_ptr->i_last_dpos)
ldir_ptr->i_last_dpos = pos;
} else {
sp = ldir_ptr->i_sp; /* 'flag' is LOOK_UP */
*numb = (ino_t) conv4(sp->s_native,
(int) dp->mfs_d_ino);
}
assert(lmfs_dev(bp) != NO_DEV);
put_block(bp, DIRECTORY_BLOCK);
return(r);
}
/* Check for free slot for the benefit of ENTER. */
if (flag == ENTER && dp->mfs_d_ino == 0) {
e_hit = TRUE; /* we found a free slot */
break;
}
}
/* The whole block has been searched or ENTER has a free slot. */
if (e_hit) break; /* e_hit set if ENTER can be performed now */
assert(lmfs_dev(bp) != NO_DEV);
put_block(bp, DIRECTORY_BLOCK); /* otherwise, continue searching dir */
}
/* The whole directory has now been searched. */
if (flag != ENTER) {
return(flag == IS_EMPTY ? OK : ENOENT);
}
/* When ENTER next time, start searching for free slot from
* i_last_dpos. It gives some performance improvement (3-5%).
*/
ldir_ptr->i_last_dpos = pos;
/* This call is for ENTER. If no free slot has been found so far, try to
* extend directory.
*/
if (e_hit == FALSE) { /* directory is full and no room left in last block */
new_slots++; /* increase directory size by 1 entry */
if (new_slots == 0) return(EFBIG); /* dir size limited by slot count */
if ( (bp = new_block(ldir_ptr, ldir_ptr->i_size)) == NULL)
return(err_code);
dp = &b_dir(bp)[0];
extended = 1;
}
/* 'bp' now points to a directory block with space. 'dp' points to slot. */
(void) memset(dp->mfs_d_name, 0, (size_t) MFS_NAME_MAX); /* clear entry */
for (i = 0; i < MFS_NAME_MAX && string[i]; i++) dp->mfs_d_name[i] = string[i];
sp = ldir_ptr->i_sp;
dp->mfs_d_ino = conv4(sp->s_native, (int) *numb);
MARKDIRTY(bp);
put_block(bp, DIRECTORY_BLOCK);
ldir_ptr->i_update |= CTIME | MTIME; /* mark mtime for update later */
IN_MARKDIRTY(ldir_ptr);
if (new_slots > old_slots) {
ldir_ptr->i_size = (off_t) new_slots * DIR_ENTRY_SIZE;
/* Send the change to disk if the directory is extended. */
if (extended) rw_inode(ldir_ptr, WRITING);
}
return(OK);
}
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