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reduce vfs_path_lookup() to do_path_lookup()

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New lookup flag: LOOKUP_ROOT.  nd->root is set (and held) by caller,
path_init() starts walking from that place and all pathname resolution
machinery never drops nd->root if that flag is set.  That turns
vfs_path_lookup() into a special case of do_path_lookup() *and*
gets us down to 3 callers of link_path_walk(), making it finally
feasible to rip the handling of trailing symlink out of link_path_walk().
That will not only simply the living hell out of it, but make life
much simpler for unionfs merge.  Trailing symlink handling will
become iterative, which is a good thing for stack footprint in
a lot of situations as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2011-03-09 23:04:47 -05:00
parent 5a18fff209
commit 5b6ca027d8
2 changed files with 44 additions and 52 deletions
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95
fs/namei.c
View File

@ -401,9 +401,11 @@ static int nameidata_drop_rcu(struct nameidata *nd)
{
struct fs_struct *fs = current->fs;
struct dentry *dentry = nd->path.dentry;
int want_root = 0;
BUG_ON(!(nd->flags & LOOKUP_RCU));
if (nd->root.mnt) {
if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
want_root = 1;
spin_lock(&fs->lock);
if (nd->root.mnt != fs->root.mnt ||
nd->root.dentry != fs->root.dentry)
@ -414,7 +416,7 @@ static int nameidata_drop_rcu(struct nameidata *nd)
goto err;
BUG_ON(nd->inode != dentry->d_inode);
spin_unlock(&dentry->d_lock);
if (nd->root.mnt) {
if (want_root) {
path_get(&nd->root);
spin_unlock(&fs->lock);
}
@ -427,7 +429,7 @@ static int nameidata_drop_rcu(struct nameidata *nd)
err:
spin_unlock(&dentry->d_lock);
err_root:
if (nd->root.mnt)
if (want_root)
spin_unlock(&fs->lock);
return -ECHILD;
}
@ -454,9 +456,11 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
{
struct fs_struct *fs = current->fs;
struct dentry *parent = nd->path.dentry;
int want_root = 0;
BUG_ON(!(nd->flags & LOOKUP_RCU));
if (nd->root.mnt) {
if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
want_root = 1;
spin_lock(&fs->lock);
if (nd->root.mnt != fs->root.mnt ||
nd->root.dentry != fs->root.dentry)
@ -476,7 +480,7 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
parent->d_count++;
spin_unlock(&dentry->d_lock);
spin_unlock(&parent->d_lock);
if (nd->root.mnt) {
if (want_root) {
path_get(&nd->root);
spin_unlock(&fs->lock);
}
@ -490,7 +494,7 @@ err:
spin_unlock(&dentry->d_lock);
spin_unlock(&parent->d_lock);
err_root:
if (nd->root.mnt)
if (want_root)
spin_unlock(&fs->lock);
return -ECHILD;
}
@ -501,7 +505,8 @@ static inline int nameidata_dentry_drop_rcu_maybe(struct nameidata *nd, struct d
if (nd->flags & LOOKUP_RCU) {
if (unlikely(nameidata_dentry_drop_rcu(nd, dentry))) {
nd->flags &= ~LOOKUP_RCU;
nd->root.mnt = NULL;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
br_read_unlock(vfsmount_lock);
return -ECHILD;
@ -525,7 +530,8 @@ static int nameidata_drop_rcu_last(struct nameidata *nd)
BUG_ON(!(nd->flags & LOOKUP_RCU));
nd->flags &= ~LOOKUP_RCU;
nd->root.mnt = NULL;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
spin_lock(&dentry->d_lock);
if (!__d_rcu_to_refcount(dentry, nd->seq))
goto err_unlock;
@ -1053,7 +1059,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
failed:
nd->flags &= ~LOOKUP_RCU;
nd->root.mnt = NULL;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
br_read_unlock(vfsmount_lock);
return -ECHILD;
@ -1310,7 +1317,8 @@ static void terminate_walk(struct nameidata *nd)
path_put(&nd->path);
} else {
nd->flags &= ~LOOKUP_RCU;
nd->root.mnt = NULL;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
rcu_read_unlock();
br_read_unlock(vfsmount_lock);
}
@ -1477,6 +1485,25 @@ static int path_init(int dfd, const char *name, unsigned int flags,
nd->last_type = LAST_ROOT; /* if there are only slashes... */
nd->flags = flags | LOOKUP_JUMPED;
nd->depth = 0;
if (flags & LOOKUP_ROOT) {
struct inode *inode = nd->root.dentry->d_inode;
if (!inode->i_op->lookup)
return -ENOTDIR;
retval = inode_permission(inode, MAY_EXEC);
if (retval)
return retval;
nd->path = nd->root;
nd->inode = inode;
if (flags & LOOKUP_RCU) {
br_read_lock(vfsmount_lock);
rcu_read_lock();
nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
} else {
path_get(&nd->path);
}
return 0;
}
nd->root.mnt = NULL;
if (*name=='/') {
@ -1587,7 +1614,7 @@ static int path_lookupat(int dfd, const char *name,
if (base)
fput(base);
if (nd->root.mnt) {
if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
path_put(&nd->root);
nd->root.mnt = NULL;
}
@ -1638,46 +1665,10 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
const char *name, unsigned int flags,
struct nameidata *nd)
{
int result;
/* same as do_path_lookup */
nd->last_type = LAST_ROOT;
nd->flags = flags | LOOKUP_JUMPED;
nd->depth = 0;
nd->path.dentry = dentry;
nd->path.mnt = mnt;
path_get(&nd->path);
nd->root = nd->path;
path_get(&nd->root);
nd->inode = nd->path.dentry->d_inode;
current->total_link_count = 0;
result = link_path_walk(name, nd);
if (!result)
result = handle_reval_path(nd);
if (result == -ESTALE) {
/* nd->path had been dropped */
current->total_link_count = 0;
nd->path.dentry = dentry;
nd->path.mnt = mnt;
nd->inode = dentry->d_inode;
path_get(&nd->path);
nd->flags = flags | LOOKUP_JUMPED | LOOKUP_REVAL;
result = link_path_walk(name, nd);
if (!result)
result = handle_reval_path(nd);
}
if (unlikely(!result && !audit_dummy_context() && nd->path.dentry &&
nd->inode))
audit_inode(name, nd->path.dentry);
path_put(&nd->root);
nd->root.mnt = NULL;
return result;
nd->root.dentry = dentry;
nd->root.mnt = mnt;
/* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */
return do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, nd);
}
static struct dentry *__lookup_hash(struct qstr *name,
@ -2320,7 +2311,7 @@ static struct file *path_openat(int dfd, const char *pathname,
path_put(&link);
}
out:
if (nd.root.mnt)
if (nd.root.mnt && !(nd.flags & LOOKUP_ROOT))
path_put(&nd.root);
if (base)
fput(base);

1
include/linux/namei.h
View File

@ -63,6 +63,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
#define LOOKUP_RENAME_TARGET 0x0800
#define LOOKUP_JUMPED 0x1000
#define LOOKUP_ROOT 0x2000
extern int user_path_at(int, const char __user *, unsigned, struct path *);