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namei.c
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namei.c
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/*
* linux/fs/namei.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
/*
* Some corrections by tytso.
*/
/* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
* lookup logic.
*/
/* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/quotaops.h>
#include <linux/pagemap.h>
#include <linux/dnotify.h>
#include <linux/smp_lock.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/mount.h>
#include <linux/audit.h>
#include <asm/namei.h>
#include <asm/uaccess.h>
#define ACC_MODE(x) ("\000\004\002\006"[(x)&O_ACCMODE])
/* [Feb-1997 T. Schoebel-Theuer]
* Fundamental changes in the pathname lookup mechanisms (namei)
* were necessary because of omirr. The reason is that omirr needs
* to know the _real_ pathname, not the user-supplied one, in case
* of symlinks (and also when transname replacements occur).
*
* The new code replaces the old recursive symlink resolution with
* an iterative one (in case of non-nested symlink chains). It does
* this with calls to <fs>_follow_link().
* As a side effect, dir_namei(), _namei() and follow_link() are now
* replaced with a single function lookup_dentry() that can handle all
* the special cases of the former code.
*
* With the new dcache, the pathname is stored at each inode, at least as
* long as the refcount of the inode is positive. As a side effect, the
* size of the dcache depends on the inode cache and thus is dynamic.
*
* [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
* resolution to correspond with current state of the code.
*
* Note that the symlink resolution is not *completely* iterative.
* There is still a significant amount of tail- and mid- recursion in
* the algorithm. Also, note that <fs>_readlink() is not used in
* lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
* may return different results than <fs>_follow_link(). Many virtual
* filesystems (including /proc) exhibit this behavior.
*/
/* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
* New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
* and the name already exists in form of a symlink, try to create the new
* name indicated by the symlink. The old code always complained that the
* name already exists, due to not following the symlink even if its target
* is nonexistent. The new semantics affects also mknod() and link() when
* the name is a symlink pointing to a non-existant name.
*
* I don't know which semantics is the right one, since I have no access
* to standards. But I found by trial that HP-UX 9.0 has the full "new"
* semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
* "old" one. Personally, I think the new semantics is much more logical.
* Note that "ln old new" where "new" is a symlink pointing to a non-existing
* file does succeed in both HP-UX and SunOs, but not in Solaris
* and in the old Linux semantics.
*/
/* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
* semantics. See the comments in "open_namei" and "do_link" below.
*
* [10-Sep-98 Alan Modra] Another symlink change.
*/
/* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
* inside the path - always follow.
* in the last component in creation/removal/renaming - never follow.
* if LOOKUP_FOLLOW passed - follow.
* if the pathname has trailing slashes - follow.
* otherwise - don't follow.
* (applied in that order).
*
* [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
* restored for 2.4. This is the last surviving part of old 4.2BSD bug.
* During the 2.4 we need to fix the userland stuff depending on it -
* hopefully we will be able to get rid of that wart in 2.5. So far only
* XEmacs seems to be relying on it...
*/
/*
* [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
* implemented. Let's see if raised priority of ->s_vfs_rename_sem gives
* any extra contention...
*/
/* In order to reduce some races, while at the same time doing additional
* checking and hopefully speeding things up, we copy filenames to the
* kernel data space before using them..
*
* POSIX.1 2.4: an empty pathname is invalid (ENOENT).
* PATH_MAX includes the nul terminator --RR.
*/
static inline int do_getname(const char __user *filename, char *page)
{
int retval;
unsigned long len = PATH_MAX;
if (!segment_eq(get_fs(), KERNEL_DS)) {
if ((unsigned long) filename >= TASK_SIZE)
return -EFAULT;
if (TASK_SIZE - (unsigned long) filename < PATH_MAX)
len = TASK_SIZE - (unsigned long) filename;
}
retval = strncpy_from_user(page, filename, len);
if (retval > 0) {
if (retval < len)
return 0;
return -ENAMETOOLONG;
} else if (!retval)
retval = -ENOENT;
return retval;
}
char * getname(const char __user * filename)
{
char *tmp, *result;
result = ERR_PTR(-ENOMEM);
tmp = __getname();
if (tmp) {
int retval = do_getname(filename, tmp);
result = tmp;
if (retval < 0) {
__putname(tmp);
result = ERR_PTR(retval);
}
}
audit_getname(result);
return result;
}
#ifdef CONFIG_AUDITSYSCALL
void putname(const char *name)
{
if (unlikely(current->audit_context))
audit_putname(name);
else
__putname(name);
}
EXPORT_SYMBOL(putname);
#endif
/**
* generic_permission - check for access rights on a Posix-like filesystem
* @inode: inode to check access rights for
* @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
* @check_acl: optional callback to check for Posix ACLs
*
* Used to check for read/write/execute permissions on a file.
* We use "fsuid" for this, letting us set arbitrary permissions
* for filesystem access without changing the "normal" uids which
* are used for other things..
*/
int generic_permission(struct inode *inode, int mask,
int (*check_acl)(struct inode *inode, int mask))
{
umode_t mode = inode->i_mode;
if (current->fsuid == inode->i_uid)
mode >>= 6;
else {
if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {
int error = check_acl(inode, mask);
if (error == -EACCES)
goto check_capabilities;
else if (error != -EAGAIN)
return error;
}
if (in_group_p(inode->i_gid))
mode >>= 3;
}
/*
* If the DACs are ok we don't need any capability check.
*/
if (((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask))
return 0;
check_capabilities:
/*
* Read/write DACs are always overridable.
* Executable DACs are overridable if at least one exec bit is set.
*/
if (!(mask & MAY_EXEC) ||
(inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode))
if (capable(CAP_DAC_OVERRIDE))
return 0;
/*
* Searching includes executable on directories, else just read.
*/
if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
if (capable(CAP_DAC_READ_SEARCH))
return 0;
return -EACCES;
}
int permission(struct inode *inode, int mask, struct nameidata *nd)
{
int retval, submask;
if (mask & MAY_WRITE) {
umode_t mode = inode->i_mode;
/*
* Nobody gets write access to a read-only fs.
*/
if (IS_RDONLY(inode) &&
(S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
return -EROFS;
/*
* Nobody gets write access to an immutable file.
*/
if (IS_IMMUTABLE(inode))
return -EACCES;
}
/* Ordinary permission routines do not understand MAY_APPEND. */
submask = mask & ~MAY_APPEND;
if (inode->i_op && inode->i_op->permission)
retval = inode->i_op->permission(inode, submask, nd);
else
retval = generic_permission(inode, submask, NULL);
if (retval)
return retval;
return security_inode_permission(inode, mask, nd);
}
/*
* get_write_access() gets write permission for a file.
* put_write_access() releases this write permission.
* This is used for regular files.
* We cannot support write (and maybe mmap read-write shared) accesses and
* MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode
* can have the following values:
* 0: no writers, no VM_DENYWRITE mappings
* < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist
* > 0: (i_writecount) users are writing to the file.
*
* Normally we operate on that counter with atomic_{inc,dec} and it's safe
* except for the cases where we don't hold i_writecount yet. Then we need to
* use {get,deny}_write_access() - these functions check the sign and refuse
* to do the change if sign is wrong. Exclusion between them is provided by
* the inode->i_lock spinlock.
*/
int get_write_access(struct inode * inode)
{
spin_lock(&inode->i_lock);
if (atomic_read(&inode->i_writecount) < 0) {
spin_unlock(&inode->i_lock);
return -ETXTBSY;
}
atomic_inc(&inode->i_writecount);
spin_unlock(&inode->i_lock);
return 0;
}
int deny_write_access(struct file * file)
{
struct inode *inode = file->f_dentry->d_inode;
spin_lock(&inode->i_lock);
if (atomic_read(&inode->i_writecount) > 0) {
spin_unlock(&inode->i_lock);
return -ETXTBSY;
}
atomic_dec(&inode->i_writecount);
spin_unlock(&inode->i_lock);
return 0;
}
void path_release(struct nameidata *nd)
{
dput(nd->dentry);
mntput(nd->mnt);
}
/*
* umount() mustn't call path_release()/mntput() as that would clear
* mnt_expiry_mark
*/
void path_release_on_umount(struct nameidata *nd)
{
dput(nd->dentry);
_mntput(nd->mnt);
}
/*
* Internal lookup() using the new generic dcache.
* SMP-safe
*/
static struct dentry * cached_lookup(struct dentry * parent, struct qstr * name, struct nameidata *nd)
{
struct dentry * dentry = __d_lookup(parent, name);
/* lockess __d_lookup may fail due to concurrent d_move()
* in some unrelated directory, so try with d_lookup
*/
if (!dentry)
dentry = d_lookup(parent, name);
if (dentry && dentry->d_op && dentry->d_op->d_revalidate) {
if (!dentry->d_op->d_revalidate(dentry, nd) && !d_invalidate(dentry)) {
dput(dentry);
dentry = NULL;
}
}
return dentry;
}
/*
* Short-cut version of permission(), for calling by
* path_walk(), when dcache lock is held. Combines parts
* of permission() and generic_permission(), and tests ONLY for
* MAY_EXEC permission.
*
* If appropriate, check DAC only. If not appropriate, or
* short-cut DAC fails, then call permission() to do more
* complete permission check.
*/
static inline int exec_permission_lite(struct inode *inode,
struct nameidata *nd)
{
umode_t mode = inode->i_mode;
if (inode->i_op && inode->i_op->permission)
return -EAGAIN;
if (current->fsuid == inode->i_uid)
mode >>= 6;
else if (in_group_p(inode->i_gid))
mode >>= 3;
if (mode & MAY_EXEC)
goto ok;
if ((inode->i_mode & S_IXUGO) && capable(CAP_DAC_OVERRIDE))
goto ok;
if (S_ISDIR(inode->i_mode) && capable(CAP_DAC_OVERRIDE))
goto ok;
if (S_ISDIR(inode->i_mode) && capable(CAP_DAC_READ_SEARCH))
goto ok;
return -EACCES;
ok:
return security_inode_permission(inode, MAY_EXEC, nd);
}
/*
* This is called when everything else fails, and we actually have
* to go to the low-level filesystem to find out what we should do..
*
* We get the directory semaphore, and after getting that we also
* make sure that nobody added the entry to the dcache in the meantime..
* SMP-safe
*/
static struct dentry * real_lookup(struct dentry * parent, struct qstr * name, struct nameidata *nd)
{
struct dentry * result;
struct inode *dir = parent->d_inode;
down(&dir->i_sem);
/*
* First re-do the cached lookup just in case it was created
* while we waited for the directory semaphore..
*
* FIXME! This could use version numbering or similar to
* avoid unnecessary cache lookups.
*
* The "dcache_lock" is purely to protect the RCU list walker
* from concurrent renames at this point (we mustn't get false
* negatives from the RCU list walk here, unlike the optimistic
* fast walk).
*
* so doing d_lookup() (with seqlock), instead of lockfree __d_lookup
*/
result = d_lookup(parent, name);
if (!result) {
struct dentry * dentry = d_alloc(parent, name);
result = ERR_PTR(-ENOMEM);
if (dentry) {
result = dir->i_op->lookup(dir, dentry, nd);
if (result)
dput(dentry);
else
result = dentry;
}
up(&dir->i_sem);
return result;
}
/*
* Uhhuh! Nasty case: the cache was re-populated while
* we waited on the semaphore. Need to revalidate.
*/
up(&dir->i_sem);
if (result->d_op && result->d_op->d_revalidate) {
if (!result->d_op->d_revalidate(result, nd) && !d_invalidate(result)) {
dput(result);
result = ERR_PTR(-ENOENT);
}
}
return result;
}
static int __emul_lookup_dentry(const char *, struct nameidata *);
/* SMP-safe */
static inline int
walk_init_root(const char *name, struct nameidata *nd)
{
read_lock(¤t->fs->lock);
if (current->fs->altroot && !(nd->flags & LOOKUP_NOALT)) {
nd->mnt = mntget(current->fs->altrootmnt);
nd->dentry = dget(current->fs->altroot);
read_unlock(¤t->fs->lock);
if (__emul_lookup_dentry(name,nd))
return 0;
read_lock(¤t->fs->lock);
}
nd->mnt = mntget(current->fs->rootmnt);
nd->dentry = dget(current->fs->root);
read_unlock(¤t->fs->lock);
return 1;
}
static inline int __vfs_follow_link(struct nameidata *nd, const char *link)
{
int res = 0;
char *name;
if (IS_ERR(link))
goto fail;
if (*link == '/') {
path_release(nd);
if (!walk_init_root(link, nd))
/* weird __emul_prefix() stuff did it */
goto out;
}
res = link_path_walk(link, nd);
out:
if (nd->depth || res || nd->last_type!=LAST_NORM)
return res;
/*
* If it is an iterative symlinks resolution in open_namei() we
* have to copy the last component. And all that crap because of
* bloody create() on broken symlinks. Furrfu...
*/
name = __getname();
if (unlikely(!name)) {
path_release(nd);
return -ENOMEM;
}
strcpy(name, nd->last.name);
nd->last.name = name;
return 0;
fail:
path_release(nd);
return PTR_ERR(link);
}
struct path {
struct vfsmount *mnt;
struct dentry *dentry;
};
static inline int __do_follow_link(struct dentry *dentry, struct nameidata *nd)
{
int error;
touch_atime(nd->mnt, dentry);
nd_set_link(nd, NULL);
error = dentry->d_inode->i_op->follow_link(dentry, nd);
if (!error) {
char *s = nd_get_link(nd);
if (s)
error = __vfs_follow_link(nd, s);
if (dentry->d_inode->i_op->put_link)
dentry->d_inode->i_op->put_link(dentry, nd);
}
return error;
}
/*
* This limits recursive symlink follows to 8, while
* limiting consecutive symlinks to 40.
*
* Without that kind of total limit, nasty chains of consecutive
* symlinks can cause almost arbitrarily long lookups.
*/
static inline int do_follow_link(struct path *path, struct nameidata *nd)
{
int err = -ELOOP;
if (current->link_count >= MAX_NESTED_LINKS)
goto loop;
if (current->total_link_count >= 40)
goto loop;
BUG_ON(nd->depth >= MAX_NESTED_LINKS);
cond_resched();
err = security_inode_follow_link(path->dentry, nd);
if (err)
goto loop;
current->link_count++;
current->total_link_count++;
nd->depth++;
err = __do_follow_link(path->dentry, nd);
current->link_count--;
nd->depth--;
return err;
loop:
path_release(nd);
return err;
}
int follow_up(struct vfsmount **mnt, struct dentry **dentry)
{
struct vfsmount *parent;
struct dentry *mountpoint;
spin_lock(&vfsmount_lock);
parent=(*mnt)->mnt_parent;
if (parent == *mnt) {
spin_unlock(&vfsmount_lock);
return 0;
}
mntget(parent);
mountpoint=dget((*mnt)->mnt_mountpoint);
spin_unlock(&vfsmount_lock);
dput(*dentry);
*dentry = mountpoint;
mntput(*mnt);
*mnt = parent;
return 1;
}
/* no need for dcache_lock, as serialization is taken care in
* namespace.c
*/
static int follow_mount(struct vfsmount **mnt, struct dentry **dentry)
{
int res = 0;
while (d_mountpoint(*dentry)) {
struct vfsmount *mounted = lookup_mnt(*mnt, *dentry);
if (!mounted)
break;
mntput(*mnt);
*mnt = mounted;
dput(*dentry);
*dentry = dget(mounted->mnt_root);
res = 1;
}
return res;
}
/* no need for dcache_lock, as serialization is taken care in
* namespace.c
*/
static inline int __follow_down(struct vfsmount **mnt, struct dentry **dentry)
{
struct vfsmount *mounted;
mounted = lookup_mnt(*mnt, *dentry);
if (mounted) {
mntput(*mnt);
*mnt = mounted;
dput(*dentry);
*dentry = dget(mounted->mnt_root);
return 1;
}
return 0;
}
int follow_down(struct vfsmount **mnt, struct dentry **dentry)
{
return __follow_down(mnt,dentry);
}
static inline void follow_dotdot(struct vfsmount **mnt, struct dentry **dentry)
{
while(1) {
struct vfsmount *parent;
struct dentry *old = *dentry;
read_lock(¤t->fs->lock);
if (*dentry == current->fs->root &&
*mnt == current->fs->rootmnt) {
read_unlock(¤t->fs->lock);
break;
}
read_unlock(¤t->fs->lock);
spin_lock(&dcache_lock);
if (*dentry != (*mnt)->mnt_root) {
*dentry = dget((*dentry)->d_parent);
spin_unlock(&dcache_lock);
dput(old);
break;
}
spin_unlock(&dcache_lock);
spin_lock(&vfsmount_lock);
parent = (*mnt)->mnt_parent;
if (parent == *mnt) {
spin_unlock(&vfsmount_lock);
break;
}
mntget(parent);
*dentry = dget((*mnt)->mnt_mountpoint);
spin_unlock(&vfsmount_lock);
dput(old);
mntput(*mnt);
*mnt = parent;
}
follow_mount(mnt, dentry);
}
/*
* It's more convoluted than I'd like it to be, but... it's still fairly
* small and for now I'd prefer to have fast path as straight as possible.
* It _is_ time-critical.
*/
static int do_lookup(struct nameidata *nd, struct qstr *name,
struct path *path)
{
struct vfsmount *mnt = nd->mnt;
struct dentry *dentry = __d_lookup(nd->dentry, name);
if (!dentry)
goto need_lookup;
if (dentry->d_op && dentry->d_op->d_revalidate)
goto need_revalidate;
done:
path->mnt = mnt;
path->dentry = dentry;
return 0;
need_lookup:
dentry = real_lookup(nd->dentry, name, nd);
if (IS_ERR(dentry))
goto fail;
goto done;
need_revalidate:
if (dentry->d_op->d_revalidate(dentry, nd))
goto done;
if (d_invalidate(dentry))
goto done;
dput(dentry);
goto need_lookup;
fail:
return PTR_ERR(dentry);
}
/*
* Name resolution.
* This is the basic name resolution function, turning a pathname into
* the final dentry. We expect 'base' to be positive and a directory.
*
* Returns 0 and nd will have valid dentry and mnt on success.
* Returns error and drops reference to input namei data on failure.
*/
static fastcall int __link_path_walk(const char * name, struct nameidata *nd)
{
struct path next;
struct inode *inode;
int err;
unsigned int lookup_flags = nd->flags;
while (*name=='/')
name++;
if (!*name)
goto return_reval;
inode = nd->dentry->d_inode;
if (nd->depth)
lookup_flags = LOOKUP_FOLLOW;
/* At this point we know we have a real path component. */
for(;;) {
unsigned long hash;
struct qstr this;
unsigned int c;
err = exec_permission_lite(inode, nd);
if (err == -EAGAIN) {
err = permission(inode, MAY_EXEC, nd);
}
if (err)
break;
this.name = name;
c = *(const unsigned char *)name;
hash = init_name_hash();
do {
name++;
hash = partial_name_hash(c, hash);
c = *(const unsigned char *)name;
} while (c && (c != '/'));
this.len = name - (const char *) this.name;
this.hash = end_name_hash(hash);
/* remove trailing slashes? */
if (!c)
goto last_component;
while (*++name == '/');
if (!*name)
goto last_with_slashes;
/*
* "." and ".." are special - ".." especially so because it has
* to be able to know about the current root directory and
* parent relationships.
*/
if (this.name[0] == '.') switch (this.len) {
default:
break;
case 2:
if (this.name[1] != '.')
break;
follow_dotdot(&nd->mnt, &nd->dentry);
inode = nd->dentry->d_inode;
/* fallthrough */
case 1:
continue;
}
/*
* See if the low-level filesystem might want
* to use its own hash..
*/
if (nd->dentry->d_op && nd->dentry->d_op->d_hash) {
err = nd->dentry->d_op->d_hash(nd->dentry, &this);
if (err < 0)
break;
}
nd->flags |= LOOKUP_CONTINUE;
/* This does the actual lookups.. */
err = do_lookup(nd, &this, &next);
if (err)
break;
/* Check mountpoints.. */
follow_mount(&next.mnt, &next.dentry);
err = -ENOENT;
inode = next.dentry->d_inode;
if (!inode)
goto out_dput;
err = -ENOTDIR;
if (!inode->i_op)
goto out_dput;
if (inode->i_op->follow_link) {
mntget(next.mnt);
err = do_follow_link(&next, nd);
dput(next.dentry);
mntput(next.mnt);
if (err)
goto return_err;
err = -ENOENT;
inode = nd->dentry->d_inode;
if (!inode)
break;
err = -ENOTDIR;
if (!inode->i_op)
break;
} else {
dput(nd->dentry);
nd->mnt = next.mnt;
nd->dentry = next.dentry;
}
err = -ENOTDIR;
if (!inode->i_op->lookup)
break;
continue;
/* here ends the main loop */
last_with_slashes:
lookup_flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
last_component:
nd->flags &= ~LOOKUP_CONTINUE;
if (lookup_flags & LOOKUP_PARENT)
goto lookup_parent;
if (this.name[0] == '.') switch (this.len) {
default:
break;
case 2:
if (this.name[1] != '.')
break;
follow_dotdot(&nd->mnt, &nd->dentry);
inode = nd->dentry->d_inode;
/* fallthrough */
case 1:
goto return_reval;
}
if (nd->dentry->d_op && nd->dentry->d_op->d_hash) {
err = nd->dentry->d_op->d_hash(nd->dentry, &this);
if (err < 0)
break;
}
err = do_lookup(nd, &this, &next);
if (err)
break;
follow_mount(&next.mnt, &next.dentry);
inode = next.dentry->d_inode;
if ((lookup_flags & LOOKUP_FOLLOW)
&& inode && inode->i_op && inode->i_op->follow_link) {
mntget(next.mnt);
err = do_follow_link(&next, nd);
dput(next.dentry);
mntput(next.mnt);
if (err)
goto return_err;
inode = nd->dentry->d_inode;
} else {
dput(nd->dentry);
nd->mnt = next.mnt;
nd->dentry = next.dentry;
}
err = -ENOENT;
if (!inode)
break;
if (lookup_flags & LOOKUP_DIRECTORY) {
err = -ENOTDIR;
if (!inode->i_op || !inode->i_op->lookup)
break;
}
goto return_base;
lookup_parent:
nd->last = this;
nd->last_type = LAST_NORM;
if (this.name[0] != '.')
goto return_base;
if (this.len == 1)
nd->last_type = LAST_DOT;
else if (this.len == 2 && this.name[1] == '.')
nd->last_type = LAST_DOTDOT;
else
goto return_base;
return_reval:
/*
* We bypassed the ordinary revalidation routines.
* We may need to check the cached dentry for staleness.
*/
if (nd->dentry && nd->dentry->d_sb &&
(nd->dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)) {
err = -ESTALE;
/* Note: we do not d_invalidate() */
if (!nd->dentry->d_op->d_revalidate(nd->dentry, nd))
break;
}
return_base:
return 0;
out_dput:
dput(next.dentry);
break;
}
path_release(nd);
return_err:
return err;
}
/*
* Wrapper to retry pathname resolution whenever the underlying
* file system returns an ESTALE.
*
* Retry the whole path once, forcing real lookup requests
* instead of relying on the dcache.
*/
int fastcall link_path_walk(const char *name, struct nameidata *nd)
{
struct nameidata save = *nd;
int result;
/* make sure the stuff we saved doesn't go away */
dget(save.dentry);
mntget(save.mnt);
result = __link_path_walk(name, nd);
if (result == -ESTALE) {
*nd = save;
dget(nd->dentry);
mntget(nd->mnt);
nd->flags |= LOOKUP_REVAL;
result = __link_path_walk(name, nd);
}
dput(save.dentry);
mntput(save.mnt);
return result;
}
int fastcall path_walk(const char * name, struct nameidata *nd)
{
current->total_link_count = 0;
return link_path_walk(name, nd);
}
/*
* SMP-safe: Returns 1 and nd will have valid dentry and mnt, if
* everything is done. Returns 0 and drops input nd, if lookup failed;
*/
static int __emul_lookup_dentry(const char *name, struct nameidata *nd)
{
if (path_walk(name, nd))
return 0; /* something went wrong... */
if (!nd->dentry->d_inode || S_ISDIR(nd->dentry->d_inode->i_mode)) {
struct dentry *old_dentry = nd->dentry;
struct vfsmount *old_mnt = nd->mnt;
struct qstr last = nd->last;
int last_type = nd->last_type;
/*
* NAME was not found in alternate root or it's a directory. Try to find
* it in the normal root:
*/
nd->last_type = LAST_ROOT;
read_lock(¤t->fs->lock);
nd->mnt = mntget(current->fs->rootmnt);
nd->dentry = dget(current->fs->root);
read_unlock(¤t->fs->lock);
if (path_walk(name, nd) == 0) {
if (nd->dentry->d_inode) {
dput(old_dentry);
mntput(old_mnt);
return 1;
}
path_release(nd);
}
nd->dentry = old_dentry;
nd->mnt = old_mnt;
nd->last = last;
nd->last_type = last_type;
}
return 1;
}
void set_fs_altroot(void)
{
char *emul = __emul_prefix();
struct nameidata nd;
struct vfsmount *mnt = NULL, *oldmnt;
struct dentry *dentry = NULL, *olddentry;
int err;
if (!emul)
goto set_it;
err = path_lookup(emul, LOOKUP_FOLLOW|LOOKUP_DIRECTORY|LOOKUP_NOALT, &nd);
if (!err) {
mnt = nd.mnt;
dentry = nd.dentry;
}
set_it:
write_lock(¤t->fs->lock);
oldmnt = current->fs->altrootmnt;
olddentry = current->fs->altroot;
current->fs->altrootmnt = mnt;
current->fs->altroot = dentry;
write_unlock(¤t->fs->lock);
if (olddentry) {
dput(olddentry);
mntput(oldmnt);
}
}
/* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
int fastcall path_lookup(const char *name, unsigned int flags, struct nameidata *nd)