// SPDX-License-Identifier: GPL-2.0-or-later
/* AFS dynamic root handling
 *
 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/dns_resolver.h>
#include "internal.h"

#define AFS_MIN_DYNROOT_CELL_INO 4 /* Allow for ., .., @cell, .@cell */
#define AFS_MAX_DYNROOT_CELL_INO ((unsigned int)INT_MAX)

static struct dentry *afs_lookup_atcell(struct inode *dir, struct dentry *dentry, ino_t ino);

/*
 * iget5() comparator for inode created by autocell operations
 */
static int afs_iget5_pseudo_test(struct inode *inode, void *opaque)
{
        struct afs_fid *fid = opaque;

        return inode->i_ino == fid->vnode;
}

/*
 * iget5() inode initialiser
 */
static int afs_iget5_pseudo_set(struct inode *inode, void *opaque)
{
        struct afs_super_info *as = AFS_FS_S(inode->i_sb);
        struct afs_vnode *vnode = AFS_FS_I(inode);
        struct afs_fid *fid = opaque;

        vnode->volume           = as->volume;
        vnode->fid              = *fid;
        inode->i_ino            = fid->vnode;
        inode->i_generation     = fid->unique;
        return 0;
}

/*
 * Create an inode for an autocell dynamic automount dir.
 */
static struct inode *afs_iget_pseudo_dir(struct super_block *sb, ino_t ino)
{
        struct afs_vnode *vnode;
        struct inode *inode;
        struct afs_fid fid = { .vnode = ino, .unique = 1, };

        _enter("");

        inode = iget5_locked(sb, fid.vnode,
                             afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
        if (!inode) {
                _leave(" = -ENOMEM");
                return ERR_PTR(-ENOMEM);
        }

        _debug("GOT INODE %p { ino=%lu, vl=%llx, vn=%llx, u=%x }",
               inode, inode->i_ino, fid.vid, fid.vnode, fid.unique);

        vnode = AFS_FS_I(inode);

        if (inode_state_read_once(inode) & I_NEW) {
                netfs_inode_init(&vnode->netfs, NULL, false);
                simple_inode_init_ts(inode);
                set_nlink(inode, 2);
                inode->i_size           = 0;
                inode->i_mode           = S_IFDIR | 0555;
                inode->i_op             = &afs_autocell_inode_operations;
                inode->i_uid            = GLOBAL_ROOT_UID;
                inode->i_gid            = GLOBAL_ROOT_GID;
                inode->i_blocks         = 0;
                inode->i_generation     = 0;
                inode->i_flags          |= S_AUTOMOUNT | S_NOATIME;

                set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
                set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);

                unlock_new_inode(inode);
        }
        _leave(" = %p", inode);
        return inode;
}

/*
 * Try to automount the mountpoint with pseudo directory, if the autocell
 * option is set.
 */
static struct dentry *afs_dynroot_lookup_cell(struct inode *dir, struct dentry *dentry,
                                              unsigned int flags)
{
        struct afs_cell *cell = NULL;
        struct afs_net *net = afs_d2net(dentry);
        struct inode *inode = NULL;
        const char *name = dentry->d_name.name;
        size_t len = dentry->d_name.len;
        bool dotted = false;
        int ret = -ENOENT;

        /* Names prefixed with a dot are R/W mounts. */
        if (name[0] == '.') {
                name++;
                len--;
                dotted = true;
        }

        cell = afs_lookup_cell(net, name, len, NULL,
                               AFS_LOOKUP_CELL_DYNROOT,
                               afs_cell_trace_use_lookup_dynroot);
        if (IS_ERR(cell)) {
                ret = PTR_ERR(cell);
                goto out_no_cell;
        }

        inode = afs_iget_pseudo_dir(dir->i_sb, cell->dynroot_ino * 2 + dotted);
        if (IS_ERR(inode)) {
                ret = PTR_ERR(inode);
                goto out;
        }

        dentry->d_fsdata = cell;
        return d_splice_alias(inode, dentry);

out:
        afs_unuse_cell(cell, afs_cell_trace_unuse_lookup_dynroot);
out_no_cell:
        if (!inode)
                return d_splice_alias(inode, dentry);
        return ret == -ENOENT ? NULL : ERR_PTR(ret);
}

/*
 * Look up an entry in a dynroot directory.
 */
static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
                                         unsigned int flags)
{
        _enter("%pd", dentry);

        if (flags & LOOKUP_CREATE)
                return ERR_PTR(-EOPNOTSUPP);

        if (dentry->d_name.len >= AFSNAMEMAX) {
                _leave(" = -ENAMETOOLONG");
                return ERR_PTR(-ENAMETOOLONG);
        }

        if (dentry->d_name.len == 5 &&
            memcmp(dentry->d_name.name, "@cell", 5) == 0)
                return afs_lookup_atcell(dir, dentry, 2);

        if (dentry->d_name.len == 6 &&
            memcmp(dentry->d_name.name, ".@cell", 6) == 0)
                return afs_lookup_atcell(dir, dentry, 3);

        return afs_dynroot_lookup_cell(dir, dentry, flags);
}

const struct inode_operations afs_dynroot_inode_operations = {
        .lookup         = afs_dynroot_lookup,
};

static void afs_dynroot_d_release(struct dentry *dentry)
{
        struct afs_cell *cell = dentry->d_fsdata;

        afs_unuse_cell(cell, afs_cell_trace_unuse_dynroot_mntpt);
}

/*
 * Keep @cell symlink dentries around, but only keep cell autodirs when they're
 * being used.
 */
static int afs_dynroot_delete_dentry(const struct dentry *dentry)
{
        const struct qstr *name = &dentry->d_name;

        if (name->len == 5 && memcmp(name->name, "@cell", 5) == 0)
                return 0;
        if (name->len == 6 && memcmp(name->name, ".@cell", 6) == 0)
                return 0;
        return 1;
}

const struct dentry_operations afs_dynroot_dentry_operations = {
        .d_delete       = afs_dynroot_delete_dentry,
        .d_release      = afs_dynroot_d_release,
        .d_automount    = afs_d_automount,
};

static void afs_atcell_delayed_put_cell(void *arg)
{
        struct afs_cell *cell = arg;

        afs_put_cell(cell, afs_cell_trace_put_atcell);
}

/*
 * Read @cell or .@cell symlinks.
 */
static const char *afs_atcell_get_link(struct dentry *dentry, struct inode *inode,
                                       struct delayed_call *done)
{
        struct afs_vnode *vnode = AFS_FS_I(inode);
        struct afs_cell *cell;
        struct afs_net *net = afs_i2net(inode);
        const char *name;
        bool dotted = vnode->fid.vnode == 3;

        if (!rcu_access_pointer(net->ws_cell))
                return ERR_PTR(-ENOENT);

        if (!dentry) {
                /* We're in RCU-pathwalk. */
                cell = rcu_dereference(net->ws_cell);
                if (dotted)
                        name = cell->name - 1;
                else
                        name = cell->name;
                /* Shouldn't need to set a delayed call. */
                return name;
        }

        down_read(&net->cells_lock);

        cell = rcu_dereference_protected(net->ws_cell, lockdep_is_held(&net->cells_lock));
        if (dotted)
                name = cell->name - 1;
        else
                name = cell->name;
        afs_get_cell(cell, afs_cell_trace_get_atcell);
        set_delayed_call(done, afs_atcell_delayed_put_cell, cell);

        up_read(&net->cells_lock);
        return name;
}

static const struct inode_operations afs_atcell_inode_operations = {
        .get_link       = afs_atcell_get_link,
};

/*
 * Create an inode for the @cell or .@cell symlinks.
 */
static struct dentry *afs_lookup_atcell(struct inode *dir, struct dentry *dentry, ino_t ino)
{
        struct afs_vnode *vnode;
        struct inode *inode;
        struct afs_fid fid = { .vnode = ino, .unique = 1, };

        inode = iget5_locked(dir->i_sb, fid.vnode,
                             afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
        if (!inode)
                return ERR_PTR(-ENOMEM);

        vnode = AFS_FS_I(inode);

        if (inode_state_read_once(inode) & I_NEW) {
                netfs_inode_init(&vnode->netfs, NULL, false);
                simple_inode_init_ts(inode);
                set_nlink(inode, 1);
                inode->i_size           = 0;
                inode->i_mode           = S_IFLNK | 0555;
                inode->i_op             = &afs_atcell_inode_operations;
                inode->i_uid            = GLOBAL_ROOT_UID;
                inode->i_gid            = GLOBAL_ROOT_GID;
                inode->i_blocks         = 0;
                inode->i_generation     = 0;
                inode->i_flags          |= S_NOATIME;

                unlock_new_inode(inode);
        }
        return d_splice_alias(inode, dentry);
}

/*
 * Transcribe the cell database into readdir content under the RCU read lock.
 * Each cell produces two entries, one prefixed with a dot and one not.
 */
static int afs_dynroot_readdir_cells(struct afs_net *net, struct dir_context *ctx)
{
        const struct afs_cell *cell;
        loff_t newpos;

        _enter("%llu", ctx->pos);

        for (;;) {
                unsigned int ix = ctx->pos >> 1;

                cell = idr_get_next(&net->cells_dyn_ino, &ix);
                if (!cell)
                        return 0;
                if (READ_ONCE(cell->state) == AFS_CELL_REMOVING ||
                    READ_ONCE(cell->state) == AFS_CELL_DEAD) {
                        ctx->pos += 2;
                        ctx->pos &= ~1;
                        continue;
                }

                newpos = ix << 1;
                if (newpos > ctx->pos)
                        ctx->pos = newpos;

                _debug("pos %llu -> cell %u", ctx->pos, cell->dynroot_ino);

                if ((ctx->pos & 1) == 0) {
                        if (!dir_emit(ctx, cell->name, cell->name_len,
                                      cell->dynroot_ino, DT_DIR))
                                return 0;
                        ctx->pos++;
                }
                if ((ctx->pos & 1) == 1) {
                        if (!dir_emit(ctx, cell->name - 1, cell->name_len + 1,
                                      cell->dynroot_ino + 1, DT_DIR))
                                return 0;
                        ctx->pos++;
                }
        }
        return 0;
}

/*
 * Read the AFS dynamic root directory.  This produces a list of cellnames,
 * dotted and undotted, along with @cell and .@cell links if configured.
 */
static int afs_dynroot_readdir(struct file *file, struct dir_context *ctx)
{
        struct afs_net *net = afs_d2net(file->f_path.dentry);
        int ret = 0;

        if (!dir_emit_dots(file, ctx))
                return 0;

        if (ctx->pos == 2) {
                if (rcu_access_pointer(net->ws_cell) &&
                    !dir_emit(ctx, "@cell", 5, 2, DT_LNK))
                        return 0;
                ctx->pos = 3;
        }
        if (ctx->pos == 3) {
                if (rcu_access_pointer(net->ws_cell) &&
                    !dir_emit(ctx, ".@cell", 6, 3, DT_LNK))
                        return 0;
                ctx->pos = 4;
        }

        if ((unsigned long long)ctx->pos <= AFS_MAX_DYNROOT_CELL_INO) {
                down_read(&net->cells_lock);
                ret = afs_dynroot_readdir_cells(net, ctx);
                up_read(&net->cells_lock);
        }
        return ret;
}

static const struct file_operations afs_dynroot_file_operations = {
        .llseek         = generic_file_llseek,
        .read           = generic_read_dir,
        .iterate_shared = afs_dynroot_readdir,
        .fsync          = noop_fsync,
};

/*
 * Create an inode for a dynamic root directory.
 */
struct inode *afs_dynroot_iget_root(struct super_block *sb)
{
        struct afs_super_info *as = AFS_FS_S(sb);
        struct afs_vnode *vnode;
        struct inode *inode;
        struct afs_fid fid = { .vid = 0, .vnode = 1, .unique = 1,};

        if (as->volume)
                fid.vid = as->volume->vid;

        inode = iget5_locked(sb, fid.vnode,
                             afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
        if (!inode)
                return ERR_PTR(-ENOMEM);

        vnode = AFS_FS_I(inode);

        /* there shouldn't be an existing inode */
        if (inode_state_read_once(inode) & I_NEW) {
                netfs_inode_init(&vnode->netfs, NULL, false);
                simple_inode_init_ts(inode);
                set_nlink(inode, 2);
                inode->i_size           = 0;
                inode->i_mode           = S_IFDIR | 0555;
                inode->i_op             = &afs_dynroot_inode_operations;
                inode->i_fop            = &afs_dynroot_file_operations;
                inode->i_uid            = GLOBAL_ROOT_UID;
                inode->i_gid            = GLOBAL_ROOT_GID;
                inode->i_blocks         = 0;
                inode->i_generation     = 0;
                inode->i_flags          |= S_NOATIME;

                set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
                unlock_new_inode(inode);
        }
        _leave(" = %p", inode);
        return inode;
}