>
> Also, to avoid code duplication, is there any reason why path_lookup()
> can't be implemented (possibly inlined) just as:
>
> static int path_lookup(const char *name, struct nameidata *nd, int flags)
> {
>
> if(!path_init(name, flags, nd))
> return 0;
>
> return path_walk(name, nd);
>
> }
Hello Paul,
Thank you for taking the time to look over my patch and sending
your comments. In response, Yes, there is a reason why I can't implement
path_lookup by calling path_init. path_init calls dget which increments
the d_count. The function I wrote holds the dcache_lock instead of
incrementing d_count at that point.
Following is the patch calling path_walk in path_init_walk
as you suggested.
Thanks for your input.
Hanna
------------
diff -Nru linux/fs/dcache.c linux-fastwalk/fs/dcache.c
--- linux/fs/dcache.c Fri Dec 21 09:41:55 2001
+++ linux-fastwalk/fs/dcache.c Wed Feb 13 11:25:44 2002
@@ -703,39 +703,45 @@
struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
{
- unsigned int len = name->len;
- unsigned int hash = name->hash;
- const unsigned char *str = name->name;
- struct list_head *head = d_hash(parent,hash);
- struct list_head *tmp;
-
- spin_lock(&dcache_lock);
- tmp = head->next;
- for (;;) {
- struct dentry * dentry = list_entry(tmp, struct dentry, d_hash);
- if (tmp == head)
- break;
- tmp = tmp->next;
- if (dentry->d_name.hash != hash)
- continue;
- if (dentry->d_parent != parent)
- continue;
- if (parent->d_op && parent->d_op->d_compare) {
- if (parent->d_op->d_compare(parent, &dentry->d_name, name))
- continue;
- } else {
- if (dentry->d_name.len != len)
- continue;
- if (memcmp(dentry->d_name.name, str, len))
- continue;
- }
- __dget_locked(dentry);
- dentry->d_vfs_flags |= DCACHE_REFERENCED;
- spin_unlock(&dcache_lock);
- return dentry;
- }
- spin_unlock(&dcache_lock);
- return NULL;
+ struct dentry *dentry = NULL;
+
+ spin_lock(&dcache_lock);
+ dentry = __d_lookup(parent, name);
+ spin_unlock(&dcache_lock);
+ return dentry;
+}
+
+struct dentry * __d_lookup(struct dentry *parent, struct qstr *name)
+{
+ unsigned int len = name->len;
+ unsigned int hash = name->hash;
+ const unsigned char *str = name->name;
+ struct list_head *head = d_hash(parent,hash);
+ struct list_head *tmp;
+
+ tmp = head->next;
+ for (;;) {
+ struct dentry * dentry = list_entry(tmp, struct dentry, d_hash);
+ if (tmp == head)
+ return NULL;
+ tmp = tmp->next;
+ if (dentry->d_name.hash != hash)
+ continue;
+ if (dentry->d_parent != parent)
+ continue;
+ if (parent->d_op && parent->d_op->d_compare) {
+ if (parent->d_op->d_compare(parent, &dentry->d_name, name))
+ continue;
+ } else {
+ if (dentry->d_name.len != len)
+ continue;
+ if (memcmp(dentry->d_name.name, str, len))
+ continue;
+ }
+ __dget_locked(dentry);
+ dentry->d_vfs_flags |= DCACHE_REFERENCED;
+ return dentry;
+ }
}
/**
diff -Nru linux/fs/exec.c linux-fastwalk/fs/exec.c
--- linux/fs/exec.c Fri Dec 21 09:41:55 2001
+++ linux-fastwalk/fs/exec.c Wed Feb 13 11:25:44 2002
@@ -343,8 +343,7 @@
struct file *file;
int err = 0;
- if (path_init(name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd))
- err = path_walk(name, &nd);
+ err = path_init_walk(name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd);
file = ERR_PTR(err);
if (!err) {
inode = nd.dentry->d_inode;
diff -Nru linux/fs/namei.c linux-fastwalk/fs/namei.c
--- linux/fs/namei.c Wed Oct 17 14:46:29 2001
+++ linux-fastwalk/fs/namei.c Thu Feb 14 14:49:51 2002
@@ -261,7 +261,13 @@
*/
static struct dentry * cached_lookup(struct dentry * parent, struct qstr * name, int flags)
{
- struct dentry * dentry = d_lookup(parent, name);
+ struct dentry *dentry = NULL;
+ if(flags & LOOKUP_LOCKED){
+ dentry = __d_lookup(parent, name);
+ spin_unlock(&dcache_lock);
+ }
+ else
+ dentry = d_lookup(parent, name);
if (dentry && dentry->d_op && dentry->d_op->d_revalidate) {
if (!dentry->d_op->d_revalidate(dentry, flags) && !d_invalidate(dentry)) {
@@ -269,6 +275,8 @@
dentry = NULL;
}
}
+ if(flags & LOOKUP_LOCKED)
+ spin_lock(&dcache_lock);
return dentry;
}
@@ -380,18 +388,18 @@
static inline int __follow_down(struct vfsmount **mnt, struct dentry **dentry)
{
- struct vfsmount *mounted;
+ struct vfsmount *mounted;
spin_lock(&dcache_lock);
- mounted = lookup_mnt(*mnt, *dentry);
- if (mounted) {
- *mnt = mntget(mounted);
- spin_unlock(&dcache_lock);
- dput(*dentry);
- mntput(mounted->mnt_parent);
- *dentry = dget(mounted->mnt_root);
- return 1;
- }
+ mounted = lookup_mnt(*mnt, *dentry);
+ if (mounted) {
+ *mnt = mntget(mounted);
+ spin_unlock(&dcache_lock);
+ dput(*dentry);
+ mntput(mounted->mnt_parent);
+ *dentry = dget(mounted->mnt_root);
+ return 1;
+ }
spin_unlock(&dcache_lock);
return 0;
}
@@ -400,6 +408,17 @@
{
return __follow_down(mnt,dentry);
}
+
+/* for fastwalking */
+static inline void undo_locked( struct nameidata *nd)
+{
+ if(nd->flags & LOOKUP_LOCKED){
+ dget(nd->dentry);
+ mntget(nd->mnt);
+ spin_unlock(&dcache_lock);
+ nd->flags &= ~LOOKUP_LOCKED;
+ }
+}
static inline void follow_dotdot(struct nameidata *nd)
{
@@ -501,6 +520,7 @@
case 2:
if (this.name[1] != '.')
break;
+ undo_locked(nd);
follow_dotdot(nd);
inode = nd->dentry->d_inode;
/* fallthrough */
@@ -516,17 +536,26 @@
if (err < 0)
break;
}
- /* This does the actual lookups.. */
- dentry = cached_lookup(nd->dentry, &this, LOOKUP_CONTINUE);
+ if(nd->flags & LOOKUP_LOCKED){
+ /* This does the actual lookups.. */
+ dentry = cached_lookup(nd->dentry, &this, LOOKUP_CONTINUE|LOOKUP_LOCKED);
+ }
+ else{
+ /* This does the actual lookups.. */
+ dentry = cached_lookup(nd->dentry, &this, LOOKUP_CONTINUE);
+ }
if (!dentry) {
+ undo_locked(nd);
dentry = real_lookup(nd->dentry, &this, LOOKUP_CONTINUE);
err = PTR_ERR(dentry);
if (IS_ERR(dentry))
break;
}
/* Check mountpoints.. */
- while (d_mountpoint(dentry) && __follow_down(&nd->mnt, &dentry))
- ;
+ if(d_mountpoint(dentry)){
+ undo_locked(nd);
+ while ( d_mountpoint(dentry) && __follow_down(&nd->mnt, &dentry));
+ }
err = -ENOENT;
inode = dentry->d_inode;
@@ -537,6 +566,7 @@
goto out_dput;
if (inode->i_op->follow_link) {
+ undo_locked(nd);
err = do_follow_link(dentry, nd);
dput(dentry);
if (err)
@@ -549,7 +579,8 @@
if (!inode->i_op)
break;
} else {
- dput(nd->dentry);
+ if (!nd->flags & LOOKUP_LOCKED)
+ dput(dentry);
nd->dentry = dentry;
}
err = -ENOTDIR;
@@ -569,6 +600,7 @@
case 2:
if (this.name[1] != '.')
break;
+ undo_locked(nd);
follow_dotdot(nd);
inode = nd->dentry->d_inode;
/* fallthrough */
@@ -580,15 +612,18 @@
if (err < 0)
break;
}
- dentry = cached_lookup(nd->dentry, &this, 0);
+ if(nd->flags & LOOKUP_LOCKED)
+ dentry = cached_lookup(nd->dentry, &this, LOOKUP_LOCKED);
+ else
+ dentry = cached_lookup(nd->dentry, &this, 0);
+ undo_locked(nd);
if (!dentry) {
dentry = real_lookup(nd->dentry, &this, 0);
err = PTR_ERR(dentry);
if (IS_ERR(dentry))
break;
}
- while (d_mountpoint(dentry) && __follow_down(&nd->mnt, &dentry))
- ;
+ while (d_mountpoint(dentry) && __follow_down(&nd->mnt, &dentry));
inode = dentry->d_inode;
if ((lookup_flags & LOOKUP_FOLLOW)
&& inode && inode->i_op && inode->i_op->follow_link) {
@@ -625,11 +660,14 @@
else if (this.len == 2 && this.name[1] == '.')
nd->last_type = LAST_DOTDOT;
return_base:
+ undo_locked(nd);
return 0;
out_dput:
+ undo_locked(nd);
dput(dentry);
break;
- }
+ } /* end of for loop */
+ undo_locked(nd);
path_release(nd);
return_err:
return err;
@@ -736,6 +774,38 @@
return 1;
}
+/* SMP-safe */
+int path_init_walk(const char *name, unsigned int flags, struct nameidata *nd)
+{
+ nd->last_type = LAST_ROOT; /* if there are only slashes... */
+ nd->flags = flags;
+ spin_lock(&dcache_lock);
+ if (*name=='/'){
+ read_lock(¤t->fs->lock);
+ if (current->fs->altroot && !(nd->flags & LOOKUP_NOALT)) {
+ nd->mnt = current->fs->altrootmnt;
+ nd->dentry = current->fs->altroot;
+ read_unlock(¤t->fs->lock);
+ spin_unlock(&dcache_lock);
+ if (__emul_lookup_dentry(name,nd))
+ return 0;
+ read_lock(¤t->fs->lock);
+ spin_lock(&dcache_lock);
+ }
+ nd->mnt = current->fs->rootmnt;
+ nd->dentry = current->fs->root;
+ read_unlock(¤t->fs->lock);
+ }
+ else{
+ read_lock(¤t->fs->lock);
+ nd->mnt = current->fs->pwdmnt;
+ nd->dentry = current->fs->pwd;
+ read_unlock(¤t->fs->lock);
+ }
+ nd->flags |= LOOKUP_LOCKED;
+ return (path_walk(name, nd));
+}
+
/*
* Restricted form of lookup. Doesn't follow links, single-component only,
* needs parent already locked. Doesn't follow mounts.
@@ -1316,8 +1386,7 @@
struct dentry *dentry;
struct nameidata nd;
- if (path_init(tmp, LOOKUP_PARENT, &nd))
- error = path_walk(tmp, &nd);
+ error = path_init_walk(tmp, LOOKUP_PARENT, &nd);
if (error)
goto out;
dentry = lookup_create(&nd, 1);
diff -Nru linux/fs/namespace.c linux-fastwalk/fs/namespace.c
--- linux/fs/namespace.c Fri Dec 21 09:41:55 2001
+++ linux-fastwalk/fs/namespace.c Wed Feb 13 11:25:44 2002
@@ -375,8 +375,7 @@
if (IS_ERR(kname))
goto out;
retval = 0;
- if (path_init(kname, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &nd))
- retval = path_walk(kname, &nd);
+ retval = path_init_walk(kname, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &nd);
putname(kname);
if (retval)
goto out;
@@ -505,8 +504,7 @@
return err;
if (!old_name || !*old_name)
return -EINVAL;
- if (path_init(old_name, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &old_nd))
- err = path_walk(old_name, &old_nd);
+ err = path_init_walk(old_name, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &old_nd);
if (err)
return err;
@@ -669,8 +667,7 @@
flags &= ~(MS_NOSUID|MS_NOEXEC|MS_NODEV);
/* ... and get the mountpoint */
- if (path_init(dir_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd))
- retval = path_walk(dir_name, &nd);
+ retval = path_init_walk(dir_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd);
if (retval)
return retval;
@@ -780,8 +777,7 @@
if (IS_ERR(name))
goto out0;
error = 0;
- if (path_init(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &new_nd))
- error = path_walk(name, &new_nd);
+ error = path_init_walk(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &new_nd);
putname(name);
if (error)
goto out0;
@@ -794,8 +790,7 @@
if (IS_ERR(name))
goto out1;
error = 0;
- if (path_init(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &old_nd))
- error = path_walk(name, &old_nd);
+ error = path_init_walk(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &old_nd);
putname(name);
if (error)
goto out1;
@@ -985,8 +980,7 @@
old_rootmnt = mntget(current->fs->rootmnt);
read_unlock(¤t->fs->lock);
/* First unmount devfs if mounted */
- if (path_init("/dev", LOOKUP_FOLLOW|LOOKUP_POSITIVE, &devfs_nd))
- error = path_walk("/dev", &devfs_nd);
+ error = path_init_walk("/dev", LOOKUP_FOLLOW|LOOKUP_POSITIVE, &devfs_nd);
if (!error) {
if (devfs_nd.mnt->mnt_sb->s_magic == DEVFS_SUPER_MAGIC &&
devfs_nd.dentry == devfs_nd.mnt->mnt_root) {
@@ -1009,8 +1003,7 @@
* Get the new mount directory
*/
error = 0;
- if (path_init(put_old, LOOKUP_FOLLOW|LOOKUP_POSITIVE|LOOKUP_DIRECTORY, &nd))
- error = path_walk(put_old, &nd);
+ error = path_init_walk(put_old, LOOKUP_FOLLOW|LOOKUP_POSITIVE|LOOKUP_DIRECTORY, &nd);
if (error) {
int blivet;
struct block_device *ramdisk = old_rootmnt->mnt_sb->s_bdev;
diff -Nru linux/fs/open.c linux-fastwalk/fs/open.c
--- linux/fs/open.c Fri Oct 12 13:48:42 2001
+++ linux-fastwalk/fs/open.c Wed Feb 13 11:25:44 2002
@@ -368,8 +368,7 @@
goto out;
error = 0;
- if (path_init(name,LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY,&nd))
- error = path_walk(name, &nd);
+ error = path_init_walk(name,LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY,&nd);
putname(name);
if (error)
goto out;
@@ -427,9 +426,8 @@
if (IS_ERR(name))
goto out;
- path_init(name, LOOKUP_POSITIVE | LOOKUP_FOLLOW |
+ error = path_init_walk(name, LOOKUP_POSITIVE | LOOKUP_FOLLOW |
LOOKUP_DIRECTORY | LOOKUP_NOALT, &nd);
- error = path_walk(name, &nd);
putname(name);
if (error)
goto out;
diff -Nru linux/fs/super.c linux-fastwalk/fs/super.c
--- linux/fs/super.c Fri Dec 21 09:42:03 2001
+++ linux-fastwalk/fs/super.c Wed Feb 13 11:25:44 2002
@@ -548,8 +548,7 @@
/* What device it is? */
if (!dev_name || !*dev_name)
return ERR_PTR(-EINVAL);
- if (path_init(dev_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd))
- error = path_walk(dev_name, &nd);
+ error = path_init_walk(dev_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd);
if (error)
return ERR_PTR(error);
inode = nd.dentry->d_inode;
diff -Nru linux/include/linux/dcache.h linux-fastwalk/include/linux/dcache.h
--- linux/include/linux/dcache.h Thu Nov 22 11:46:18 2001
+++ linux-fastwalk/include/linux/dcache.h Wed Feb 13 11:25:44 2002
@@ -218,6 +218,7 @@
/* appendix may either be NULL or be used for transname suffixes */
extern struct dentry * d_lookup(struct dentry *, struct qstr *);
+extern struct dentry * __d_lookup(struct dentry *, struct qstr *);
/* validate "insecure" dentry pointer */
extern int d_validate(struct dentry *, struct dentry *);
diff -Nru linux/include/linux/fs.h linux-fastwalk/include/linux/fs.h
--- linux/include/linux/fs.h Fri Dec 21 09:42:03 2001
+++ linux-fastwalk/include/linux/fs.h Wed Feb 13 11:25:44 2002
@@ -1270,6 +1270,7 @@
* - require a directory
* - ending slashes ok even for nonexistent files
* - internal "there are more path compnents" flag
+ * - locked on when the dcache_lock is held
*/
#define LOOKUP_FOLLOW (1)
#define LOOKUP_DIRECTORY (2)
@@ -1277,6 +1278,8 @@
#define LOOKUP_POSITIVE (8)
#define LOOKUP_PARENT (16)
#define LOOKUP_NOALT (32)
+#define LOOKUP_LOCKED (64)
+
/*
* Type of the last component on LOOKUP_PARENT
*/
@@ -1306,6 +1309,7 @@
extern int FASTCALL(__user_walk(const char *, unsigned, struct nameidata *));
extern int FASTCALL(path_init(const char *, unsigned, struct nameidata *));
extern int FASTCALL(path_walk(const char *, struct nameidata *));
+extern int FASTCALL(path_init_walk(const char *, unsigned, struct nameidata *));
extern int FASTCALL(link_path_walk(const char *, struct nameidata *));
extern void path_release(struct nameidata *);
extern int follow_down(struct vfsmount **, struct dentry **);
diff -Nru linux/kernel/ksyms.c linux-fastwalk/kernel/ksyms.c
--- linux/kernel/ksyms.c Fri Dec 21 09:42:04 2001
+++ linux-fastwalk/kernel/ksyms.c Wed Feb 13 11:25:44 2002
@@ -144,6 +144,7 @@
EXPORT_SYMBOL(lookup_mnt);
EXPORT_SYMBOL(path_init);
EXPORT_SYMBOL(path_walk);
+EXPORT_SYMBOL(path_init_walk);
EXPORT_SYMBOL(path_release);
EXPORT_SYMBOL(__user_walk);
EXPORT_SYMBOL(lookup_one_len);
-
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