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![Amir Goldstein](/assets/img/avatar_default.png)
On lookup of non directory, we try to decode the origin file handle stored in upper inode. The origin file handle is supposed to be decoded to a disconnected non-dir dentry, which is fine, because we only need the lower inode of a copy up origin. However, if the origin file handle somehow turns out to be a directory we pay the expensive cost of reconnecting the directory dentry, only to get a mismatch file type and drop the dentry. Optimize this case by explicitly opting out of reconnecting the dentry. Opting-out of reconnect is done by passing a NULL acceptable callback to exportfs_decode_fh(). While the case described above is a strange corner case that does not really need to be optimized, the API added for this optimization will be used by a following patch to optimize a more common case of decoding an overlayfs file handle. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
561 lines
14 KiB
C
561 lines
14 KiB
C
/*
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* Copyright (C) Neil Brown 2002
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* Copyright (C) Christoph Hellwig 2007
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*
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* This file contains the code mapping from inodes to NFS file handles,
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* and for mapping back from file handles to dentries.
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*
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* For details on why we do all the strange and hairy things in here
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* take a look at Documentation/filesystems/nfs/Exporting.
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*/
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#include <linux/exportfs.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/module.h>
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#include <linux/mount.h>
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#include <linux/namei.h>
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#include <linux/sched.h>
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#include <linux/cred.h>
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#define dprintk(fmt, args...) do{}while(0)
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static int get_name(const struct path *path, char *name, struct dentry *child);
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static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
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char *name, struct dentry *child)
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{
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const struct export_operations *nop = dir->d_sb->s_export_op;
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struct path path = {.mnt = mnt, .dentry = dir};
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if (nop->get_name)
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return nop->get_name(dir, name, child);
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else
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return get_name(&path, name, child);
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}
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/*
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* Check if the dentry or any of it's aliases is acceptable.
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*/
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static struct dentry *
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find_acceptable_alias(struct dentry *result,
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int (*acceptable)(void *context, struct dentry *dentry),
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void *context)
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{
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struct dentry *dentry, *toput = NULL;
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struct inode *inode;
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if (acceptable(context, result))
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return result;
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inode = result->d_inode;
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spin_lock(&inode->i_lock);
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hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
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dget(dentry);
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spin_unlock(&inode->i_lock);
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if (toput)
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dput(toput);
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if (dentry != result && acceptable(context, dentry)) {
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dput(result);
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return dentry;
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}
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spin_lock(&inode->i_lock);
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toput = dentry;
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}
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spin_unlock(&inode->i_lock);
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if (toput)
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dput(toput);
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return NULL;
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}
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static bool dentry_connected(struct dentry *dentry)
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{
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dget(dentry);
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while (dentry->d_flags & DCACHE_DISCONNECTED) {
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struct dentry *parent = dget_parent(dentry);
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dput(dentry);
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if (IS_ROOT(dentry)) {
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dput(parent);
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return false;
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}
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dentry = parent;
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}
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dput(dentry);
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return true;
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}
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static void clear_disconnected(struct dentry *dentry)
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{
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dget(dentry);
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while (dentry->d_flags & DCACHE_DISCONNECTED) {
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struct dentry *parent = dget_parent(dentry);
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WARN_ON_ONCE(IS_ROOT(dentry));
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spin_lock(&dentry->d_lock);
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dentry->d_flags &= ~DCACHE_DISCONNECTED;
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spin_unlock(&dentry->d_lock);
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dput(dentry);
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dentry = parent;
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}
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dput(dentry);
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}
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/*
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* Reconnect a directory dentry with its parent.
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*
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* This can return a dentry, or NULL, or an error.
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*
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* In the first case the returned dentry is the parent of the given
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* dentry, and may itself need to be reconnected to its parent.
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*
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* In the NULL case, a concurrent VFS operation has either renamed or
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* removed this directory. The concurrent operation has reconnected our
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* dentry, so we no longer need to.
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*/
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static struct dentry *reconnect_one(struct vfsmount *mnt,
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struct dentry *dentry, char *nbuf)
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{
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struct dentry *parent;
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struct dentry *tmp;
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int err;
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parent = ERR_PTR(-EACCES);
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inode_lock(dentry->d_inode);
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if (mnt->mnt_sb->s_export_op->get_parent)
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parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
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inode_unlock(dentry->d_inode);
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if (IS_ERR(parent)) {
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dprintk("%s: get_parent of %ld failed, err %d\n",
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__func__, dentry->d_inode->i_ino, PTR_ERR(parent));
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return parent;
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}
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dprintk("%s: find name of %lu in %lu\n", __func__,
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dentry->d_inode->i_ino, parent->d_inode->i_ino);
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err = exportfs_get_name(mnt, parent, nbuf, dentry);
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if (err == -ENOENT)
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goto out_reconnected;
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if (err)
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goto out_err;
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dprintk("%s: found name: %s\n", __func__, nbuf);
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tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
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if (IS_ERR(tmp)) {
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dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
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goto out_err;
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}
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if (tmp != dentry) {
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/*
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* Somebody has renamed it since exportfs_get_name();
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* great, since it could've only been renamed if it
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* got looked up and thus connected, and it would
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* remain connected afterwards. We are done.
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*/
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dput(tmp);
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goto out_reconnected;
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}
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dput(tmp);
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if (IS_ROOT(dentry)) {
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err = -ESTALE;
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goto out_err;
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}
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return parent;
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out_err:
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dput(parent);
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return ERR_PTR(err);
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out_reconnected:
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dput(parent);
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/*
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* Someone must have renamed our entry into another parent, in
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* which case it has been reconnected by the rename.
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*
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* Or someone removed it entirely, in which case filehandle
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* lookup will succeed but the directory is now IS_DEAD and
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* subsequent operations on it will fail.
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*
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* Alternatively, maybe there was no race at all, and the
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* filesystem is just corrupt and gave us a parent that doesn't
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* actually contain any entry pointing to this inode. So,
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* double check that this worked and return -ESTALE if not:
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*/
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if (!dentry_connected(dentry))
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return ERR_PTR(-ESTALE);
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return NULL;
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}
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/*
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* Make sure target_dir is fully connected to the dentry tree.
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*
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* On successful return, DCACHE_DISCONNECTED will be cleared on
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* target_dir, and target_dir->d_parent->...->d_parent will reach the
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* root of the filesystem.
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*
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* Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
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* But the converse is not true: target_dir may have DCACHE_DISCONNECTED
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* set but already be connected. In that case we'll verify the
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* connection to root and then clear the flag.
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*
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* Note that target_dir could be removed by a concurrent operation. In
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* that case reconnect_path may still succeed with target_dir fully
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* connected, but further operations using the filehandle will fail when
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* necessary (due to S_DEAD being set on the directory).
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*/
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static int
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reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
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{
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struct dentry *dentry, *parent;
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dentry = dget(target_dir);
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while (dentry->d_flags & DCACHE_DISCONNECTED) {
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BUG_ON(dentry == mnt->mnt_sb->s_root);
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if (IS_ROOT(dentry))
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parent = reconnect_one(mnt, dentry, nbuf);
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else
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parent = dget_parent(dentry);
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if (!parent)
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break;
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dput(dentry);
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if (IS_ERR(parent))
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return PTR_ERR(parent);
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dentry = parent;
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}
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dput(dentry);
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clear_disconnected(target_dir);
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return 0;
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}
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struct getdents_callback {
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struct dir_context ctx;
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char *name; /* name that was found. It already points to a
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buffer NAME_MAX+1 is size */
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u64 ino; /* the inum we are looking for */
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int found; /* inode matched? */
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int sequence; /* sequence counter */
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};
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/*
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* A rather strange filldir function to capture
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* the name matching the specified inode number.
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*/
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static int filldir_one(struct dir_context *ctx, const char *name, int len,
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loff_t pos, u64 ino, unsigned int d_type)
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{
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struct getdents_callback *buf =
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container_of(ctx, struct getdents_callback, ctx);
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int result = 0;
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buf->sequence++;
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if (buf->ino == ino && len <= NAME_MAX) {
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memcpy(buf->name, name, len);
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buf->name[len] = '\0';
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buf->found = 1;
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result = -1;
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}
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return result;
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}
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/**
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* get_name - default export_operations->get_name function
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* @path: the directory in which to find a name
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* @name: a pointer to a %NAME_MAX+1 char buffer to store the name
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* @child: the dentry for the child directory.
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*
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* calls readdir on the parent until it finds an entry with
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* the same inode number as the child, and returns that.
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*/
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static int get_name(const struct path *path, char *name, struct dentry *child)
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{
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const struct cred *cred = current_cred();
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struct inode *dir = path->dentry->d_inode;
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int error;
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struct file *file;
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struct kstat stat;
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struct path child_path = {
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.mnt = path->mnt,
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.dentry = child,
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};
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struct getdents_callback buffer = {
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.ctx.actor = filldir_one,
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.name = name,
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};
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error = -ENOTDIR;
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if (!dir || !S_ISDIR(dir->i_mode))
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goto out;
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error = -EINVAL;
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if (!dir->i_fop)
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goto out;
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/*
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* inode->i_ino is unsigned long, kstat->ino is u64, so the
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* former would be insufficient on 32-bit hosts when the
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* filesystem supports 64-bit inode numbers. So we need to
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* actually call ->getattr, not just read i_ino:
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*/
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error = vfs_getattr_nosec(&child_path, &stat,
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STATX_INO, AT_STATX_SYNC_AS_STAT);
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if (error)
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return error;
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buffer.ino = stat.ino;
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/*
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* Open the directory ...
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*/
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file = dentry_open(path, O_RDONLY, cred);
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error = PTR_ERR(file);
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if (IS_ERR(file))
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goto out;
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error = -EINVAL;
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if (!file->f_op->iterate && !file->f_op->iterate_shared)
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goto out_close;
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buffer.sequence = 0;
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while (1) {
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int old_seq = buffer.sequence;
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error = iterate_dir(file, &buffer.ctx);
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if (buffer.found) {
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error = 0;
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break;
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}
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if (error < 0)
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break;
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error = -ENOENT;
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if (old_seq == buffer.sequence)
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break;
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}
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out_close:
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fput(file);
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out:
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return error;
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}
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/**
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* export_encode_fh - default export_operations->encode_fh function
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* @inode: the object to encode
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* @fid: where to store the file handle fragment
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* @max_len: maximum length to store there
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* @parent: parent directory inode, if wanted
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*
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* This default encode_fh function assumes that the 32 inode number
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* is suitable for locating an inode, and that the generation number
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* can be used to check that it is still valid. It places them in the
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* filehandle fragment where export_decode_fh expects to find them.
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*/
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static int export_encode_fh(struct inode *inode, struct fid *fid,
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int *max_len, struct inode *parent)
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{
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int len = *max_len;
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int type = FILEID_INO32_GEN;
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if (parent && (len < 4)) {
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*max_len = 4;
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return FILEID_INVALID;
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} else if (len < 2) {
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*max_len = 2;
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return FILEID_INVALID;
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}
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len = 2;
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fid->i32.ino = inode->i_ino;
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fid->i32.gen = inode->i_generation;
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if (parent) {
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fid->i32.parent_ino = parent->i_ino;
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fid->i32.parent_gen = parent->i_generation;
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len = 4;
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type = FILEID_INO32_GEN_PARENT;
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}
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*max_len = len;
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return type;
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}
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int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
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int *max_len, struct inode *parent)
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{
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const struct export_operations *nop = inode->i_sb->s_export_op;
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if (nop && nop->encode_fh)
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return nop->encode_fh(inode, fid->raw, max_len, parent);
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return export_encode_fh(inode, fid, max_len, parent);
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}
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EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
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int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
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int connectable)
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{
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int error;
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struct dentry *p = NULL;
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struct inode *inode = dentry->d_inode, *parent = NULL;
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if (connectable && !S_ISDIR(inode->i_mode)) {
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p = dget_parent(dentry);
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/*
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* note that while p might've ceased to be our parent already,
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* it's still pinned by and still positive.
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*/
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parent = p->d_inode;
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}
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error = exportfs_encode_inode_fh(inode, fid, max_len, parent);
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dput(p);
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return error;
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}
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EXPORT_SYMBOL_GPL(exportfs_encode_fh);
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struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
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int fh_len, int fileid_type,
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int (*acceptable)(void *, struct dentry *), void *context)
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{
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const struct export_operations *nop = mnt->mnt_sb->s_export_op;
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struct dentry *result, *alias;
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char nbuf[NAME_MAX+1];
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int err;
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/*
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* Try to get any dentry for the given file handle from the filesystem.
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*/
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if (!nop || !nop->fh_to_dentry)
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return ERR_PTR(-ESTALE);
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result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
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if (PTR_ERR(result) == -ENOMEM)
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return ERR_CAST(result);
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if (IS_ERR_OR_NULL(result))
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return ERR_PTR(-ESTALE);
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/*
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* If no acceptance criteria was specified by caller, a disconnected
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* dentry is also accepatable. Callers may use this mode to query if
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* file handle is stale or to get a reference to an inode without
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* risking the high overhead caused by directory reconnect.
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*/
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if (!acceptable)
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return result;
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if (d_is_dir(result)) {
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/*
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* This request is for a directory.
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*
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* On the positive side there is only one dentry for each
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* directory inode. On the negative side this implies that we
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* to ensure our dentry is connected all the way up to the
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* filesystem root.
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*/
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if (result->d_flags & DCACHE_DISCONNECTED) {
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err = reconnect_path(mnt, result, nbuf);
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if (err)
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goto err_result;
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}
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if (!acceptable(context, result)) {
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err = -EACCES;
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goto err_result;
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}
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return result;
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} else {
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/*
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* It's not a directory. Life is a little more complicated.
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*/
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struct dentry *target_dir, *nresult;
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/*
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* See if either the dentry we just got from the filesystem
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* or any alias for it is acceptable. This is always true
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* if this filesystem is exported without the subtreecheck
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* option. If the filesystem is exported with the subtree
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* check option there's a fair chance we need to look at
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* the parent directory in the file handle and make sure
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* it's connected to the filesystem root.
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*/
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alias = find_acceptable_alias(result, acceptable, context);
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if (alias)
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return alias;
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/*
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* Try to extract a dentry for the parent directory from the
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* file handle. If this fails we'll have to give up.
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*/
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err = -ESTALE;
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if (!nop->fh_to_parent)
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goto err_result;
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target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
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fh_len, fileid_type);
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if (!target_dir)
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goto err_result;
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err = PTR_ERR(target_dir);
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if (IS_ERR(target_dir))
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goto err_result;
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/*
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* And as usual we need to make sure the parent directory is
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* connected to the filesystem root. The VFS really doesn't
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* like disconnected directories..
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*/
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err = reconnect_path(mnt, target_dir, nbuf);
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if (err) {
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dput(target_dir);
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goto err_result;
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}
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/*
|
|
* Now that we've got both a well-connected parent and a
|
|
* dentry for the inode we're after, make sure that our
|
|
* inode is actually connected to the parent.
|
|
*/
|
|
err = exportfs_get_name(mnt, target_dir, nbuf, result);
|
|
if (!err) {
|
|
inode_lock(target_dir->d_inode);
|
|
nresult = lookup_one_len(nbuf, target_dir,
|
|
strlen(nbuf));
|
|
inode_unlock(target_dir->d_inode);
|
|
if (!IS_ERR(nresult)) {
|
|
if (nresult->d_inode) {
|
|
dput(result);
|
|
result = nresult;
|
|
} else
|
|
dput(nresult);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* At this point we are done with the parent, but it's pinned
|
|
* by the child dentry anyway.
|
|
*/
|
|
dput(target_dir);
|
|
|
|
/*
|
|
* And finally make sure the dentry is actually acceptable
|
|
* to NFSD.
|
|
*/
|
|
alias = find_acceptable_alias(result, acceptable, context);
|
|
if (!alias) {
|
|
err = -EACCES;
|
|
goto err_result;
|
|
}
|
|
|
|
return alias;
|
|
}
|
|
|
|
err_result:
|
|
dput(result);
|
|
if (err != -ENOMEM)
|
|
err = -ESTALE;
|
|
return ERR_PTR(err);
|
|
}
|
|
EXPORT_SYMBOL_GPL(exportfs_decode_fh);
|
|
|
|
MODULE_LICENSE("GPL");
|