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![David Howells](/assets/img/avatar_default.png)
Fix the lookup method on the dynamic root directory such that creation calls, such as mkdir, open(O_CREAT), symlink, etc. fail with EOPNOTSUPP rather than failing with some odd error (such as EEXIST). lookup() itself tries to create automount directories when it is invoked. These are cached locally in RAM and not committed to storage. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Marc Dionne <marc.dionne@auristor.com> Tested-by: Jonathan Billings <jsbillings@jsbillings.org>
303 lines
6.7 KiB
C
303 lines
6.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* AFS dynamic root handling
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*
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* Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#include <linux/fs.h>
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#include <linux/namei.h>
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#include <linux/dns_resolver.h>
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#include "internal.h"
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/*
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* Probe to see if a cell may exist. This prevents positive dentries from
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* being created unnecessarily.
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*/
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static int afs_probe_cell_name(struct dentry *dentry)
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{
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struct afs_cell *cell;
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struct afs_net *net = afs_d2net(dentry);
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const char *name = dentry->d_name.name;
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size_t len = dentry->d_name.len;
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int ret;
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/* Names prefixed with a dot are R/W mounts. */
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if (name[0] == '.') {
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if (len == 1)
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return -EINVAL;
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name++;
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len--;
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}
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cell = afs_lookup_cell_rcu(net, name, len);
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if (!IS_ERR(cell)) {
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afs_put_cell(net, cell);
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return 0;
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}
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ret = dns_query(net->net, "afsdb", name, len, "srv=1",
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NULL, NULL, false);
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if (ret == -ENODATA)
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ret = -EDESTADDRREQ;
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return ret;
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}
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/*
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* Try to auto mount the mountpoint with pseudo directory, if the autocell
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* operation is setted.
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*/
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struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
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{
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struct afs_vnode *vnode = AFS_FS_I(dir);
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struct inode *inode;
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int ret = -ENOENT;
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_enter("%p{%pd}, {%llx:%llu}",
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dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
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if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
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goto out;
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ret = afs_probe_cell_name(dentry);
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if (ret < 0)
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goto out;
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inode = afs_iget_pseudo_dir(dir->i_sb, false);
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if (IS_ERR(inode)) {
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ret = PTR_ERR(inode);
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goto out;
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}
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_leave("= %p", inode);
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return inode;
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out:
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_leave("= %d", ret);
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return ret == -ENOENT ? NULL : ERR_PTR(ret);
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}
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/*
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* Look up @cell in a dynroot directory. This is a substitution for the
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* local cell name for the net namespace.
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*/
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static struct dentry *afs_lookup_atcell(struct dentry *dentry)
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{
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struct afs_cell *cell;
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struct afs_net *net = afs_d2net(dentry);
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struct dentry *ret;
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unsigned int seq = 0;
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char *name;
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int len;
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if (!net->ws_cell)
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return ERR_PTR(-ENOENT);
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ret = ERR_PTR(-ENOMEM);
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name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
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if (!name)
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goto out_p;
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rcu_read_lock();
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do {
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read_seqbegin_or_lock(&net->cells_lock, &seq);
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cell = rcu_dereference_raw(net->ws_cell);
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if (cell) {
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len = cell->name_len;
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memcpy(name, cell->name, len + 1);
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}
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} while (need_seqretry(&net->cells_lock, seq));
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done_seqretry(&net->cells_lock, seq);
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rcu_read_unlock();
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ret = ERR_PTR(-ENOENT);
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if (!cell)
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goto out_n;
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ret = lookup_one_len(name, dentry->d_parent, len);
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/* We don't want to d_add() the @cell dentry here as we don't want to
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* the cached dentry to hide changes to the local cell name.
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*/
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out_n:
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kfree(name);
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out_p:
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return ret;
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}
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/*
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* Look up an entry in a dynroot directory.
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*/
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static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
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unsigned int flags)
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{
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_enter("%pd", dentry);
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ASSERTCMP(d_inode(dentry), ==, NULL);
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if (flags & LOOKUP_CREATE)
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return ERR_PTR(-EOPNOTSUPP);
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if (dentry->d_name.len >= AFSNAMEMAX) {
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_leave(" = -ENAMETOOLONG");
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return ERR_PTR(-ENAMETOOLONG);
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}
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if (dentry->d_name.len == 5 &&
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memcmp(dentry->d_name.name, "@cell", 5) == 0)
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return afs_lookup_atcell(dentry);
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return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
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}
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const struct inode_operations afs_dynroot_inode_operations = {
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.lookup = afs_dynroot_lookup,
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};
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/*
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* Dirs in the dynamic root don't need revalidation.
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*/
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static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
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{
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return 1;
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}
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/*
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* Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
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* sleep)
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* - called from dput() when d_count is going to 0.
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* - return 1 to request dentry be unhashed, 0 otherwise
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*/
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static int afs_dynroot_d_delete(const struct dentry *dentry)
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{
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return d_really_is_positive(dentry);
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}
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const struct dentry_operations afs_dynroot_dentry_operations = {
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.d_revalidate = afs_dynroot_d_revalidate,
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.d_delete = afs_dynroot_d_delete,
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.d_release = afs_d_release,
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.d_automount = afs_d_automount,
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};
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/*
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* Create a manually added cell mount directory.
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* - The caller must hold net->proc_cells_lock
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*/
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int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
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{
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struct super_block *sb = net->dynroot_sb;
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struct dentry *root, *subdir;
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int ret;
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if (!sb || atomic_read(&sb->s_active) == 0)
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return 0;
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/* Let the ->lookup op do the creation */
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root = sb->s_root;
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inode_lock(root->d_inode);
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subdir = lookup_one_len(cell->name, root, cell->name_len);
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if (IS_ERR(subdir)) {
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ret = PTR_ERR(subdir);
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goto unlock;
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}
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/* Note that we're retaining an extra ref on the dentry */
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subdir->d_fsdata = (void *)1UL;
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ret = 0;
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unlock:
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inode_unlock(root->d_inode);
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return ret;
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}
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/*
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* Remove a manually added cell mount directory.
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* - The caller must hold net->proc_cells_lock
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*/
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void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
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{
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struct super_block *sb = net->dynroot_sb;
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struct dentry *root, *subdir;
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if (!sb || atomic_read(&sb->s_active) == 0)
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return;
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root = sb->s_root;
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inode_lock(root->d_inode);
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/* Don't want to trigger a lookup call, which will re-add the cell */
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subdir = try_lookup_one_len(cell->name, root, cell->name_len);
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if (IS_ERR_OR_NULL(subdir)) {
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_debug("lookup %ld", PTR_ERR(subdir));
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goto no_dentry;
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}
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_debug("rmdir %pd %u", subdir, d_count(subdir));
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if (subdir->d_fsdata) {
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_debug("unpin %u", d_count(subdir));
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subdir->d_fsdata = NULL;
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dput(subdir);
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}
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dput(subdir);
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no_dentry:
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inode_unlock(root->d_inode);
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_leave("");
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}
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/*
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* Populate a newly created dynamic root with cell names.
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*/
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int afs_dynroot_populate(struct super_block *sb)
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{
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struct afs_cell *cell;
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struct afs_net *net = afs_sb2net(sb);
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int ret;
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mutex_lock(&net->proc_cells_lock);
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net->dynroot_sb = sb;
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hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
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ret = afs_dynroot_mkdir(net, cell);
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if (ret < 0)
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goto error;
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}
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ret = 0;
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out:
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mutex_unlock(&net->proc_cells_lock);
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return ret;
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error:
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net->dynroot_sb = NULL;
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goto out;
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}
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/*
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* When a dynamic root that's in the process of being destroyed, depopulate it
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* of pinned directories.
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*/
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void afs_dynroot_depopulate(struct super_block *sb)
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{
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struct afs_net *net = afs_sb2net(sb);
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struct dentry *root = sb->s_root, *subdir, *tmp;
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/* Prevent more subdirs from being created */
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mutex_lock(&net->proc_cells_lock);
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if (net->dynroot_sb == sb)
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net->dynroot_sb = NULL;
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mutex_unlock(&net->proc_cells_lock);
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inode_lock(root->d_inode);
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/* Remove all the pins for dirs created for manually added cells */
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list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
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if (subdir->d_fsdata) {
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subdir->d_fsdata = NULL;
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dput(subdir);
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}
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}
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inode_unlock(root->d_inode);
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}
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