/*
 * V9FS FID Management
 *
 *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
 *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to:
 *  Free Software Foundation
 *  51 Franklin Street, Fifth Floor
 *  Boston, MA  02111-1301  USA
 *
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/idr.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>

#include "v9fs.h"
#include "v9fs_vfs.h"
#include "fid.h"

/**
 * v9fs_fid_add - add a fid to a dentry
 * @dentry: dentry that the fid is being added to
 * @fid: fid to add
 *
 */

static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
{
        hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
}

void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
{
        spin_lock(&dentry->d_lock);
        __add_fid(dentry, fid);
        spin_unlock(&dentry->d_lock);
}

/**
 * v9fs_fid_find - retrieve a fid that belongs to the specified uid
 * @dentry: dentry to look for fid in
 * @uid: return fid that belongs to the specified user
 * @any: if non-zero, return any fid associated with the dentry
 *
 */

static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
{
        struct p9_fid *fid, *ret;

        p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p) uid %d any %d\n",
                 dentry, dentry, from_kuid(&init_user_ns, uid),
                 any);
        ret = NULL;
        /* we'll recheck under lock if there's anything to look in */
        if (dentry->d_fsdata) {
                struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
                spin_lock(&dentry->d_lock);
                hlist_for_each_entry(fid, h, dlist) {
                        if (any || uid_eq(fid->uid, uid)) {
                                ret = fid;
                                break;
                        }
                }
                spin_unlock(&dentry->d_lock);
        }

        return ret;
}

/*
 * We need to hold v9ses->rename_sem as long as we hold references
 * to returned path array. Array element contain pointers to
 * dentry names.
 */
static int build_path_from_dentry(struct v9fs_session_info *v9ses,
                                  struct dentry *dentry, const unsigned char ***names)
{
        int n = 0, i;
        const unsigned char **wnames;
        struct dentry *ds;

        for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
                n++;

        wnames = kmalloc_array(n, sizeof(char *), GFP_KERNEL);
        if (!wnames)
                goto err_out;

        for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
                wnames[i] = ds->d_name.name;

        *names = wnames;
        return n;
err_out:
        return -ENOMEM;
}

static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
                                               kuid_t uid, int any)
{
        struct dentry *ds;
        const unsigned char **wnames, *uname;
        int i, n, l, clone, access;
        struct v9fs_session_info *v9ses;
        struct p9_fid *fid, *old_fid = NULL;

        v9ses = v9fs_dentry2v9ses(dentry);
        access = v9ses->flags & V9FS_ACCESS_MASK;
        fid = v9fs_fid_find(dentry, uid, any);
        if (fid)
                return fid;
        /*
         * we don't have a matching fid. To do a TWALK we need
         * parent fid. We need to prevent rename when we want to
         * look at the parent.
         */
        down_read(&v9ses->rename_sem);
        ds = dentry->d_parent;
        fid = v9fs_fid_find(ds, uid, any);
        if (fid) {
                /* Found the parent fid do a lookup with that */
                fid = p9_client_walk(fid, 1, &dentry->d_name.name, 1);
                goto fid_out;
        }
        up_read(&v9ses->rename_sem);

        /* start from the root and try to do a lookup */
        fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
        if (!fid) {
                /* the user is not attached to the fs yet */
                if (access == V9FS_ACCESS_SINGLE)
                        return ERR_PTR(-EPERM);

                if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
                                uname = NULL;
                else
                        uname = v9ses->uname;

                fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
                                       v9ses->aname);
                if (IS_ERR(fid))
                        return fid;

                v9fs_fid_add(dentry->d_sb->s_root, fid);
        }
        /* If we are root ourself just return that */
        if (dentry->d_sb->s_root == dentry)
                return fid;
        /*
         * Do a multipath walk with attached root.
         * When walking parent we need to make sure we
         * don't have a parallel rename happening
         */
        down_read(&v9ses->rename_sem);
        n  = build_path_from_dentry(v9ses, dentry, &wnames);
        if (n < 0) {
                fid = ERR_PTR(n);
                goto err_out;
        }
        clone = 1;
        i = 0;
        while (i < n) {
                l = min(n - i, P9_MAXWELEM);
                /*
                 * We need to hold rename lock when doing a multipath
                 * walk to ensure none of the patch component change
                 */
                fid = p9_client_walk(fid, l, &wnames[i], clone);
                if (IS_ERR(fid)) {
                        if (old_fid) {
                                /*
                                 * If we fail, clunk fid which are mapping
                                 * to path component and not the last component
                                 * of the path.
                                 */
                                p9_client_clunk(old_fid);
                        }
                        kfree(wnames);
                        goto err_out;
                }
                old_fid = fid;
                i += l;
                clone = 0;
        }
        kfree(wnames);
fid_out:
        if (!IS_ERR(fid)) {
                spin_lock(&dentry->d_lock);
                if (d_unhashed(dentry)) {
                        spin_unlock(&dentry->d_lock);
                        p9_client_clunk(fid);
                        fid = ERR_PTR(-ENOENT);
                } else {
                        __add_fid(dentry, fid);
                        spin_unlock(&dentry->d_lock);
                }
        }
err_out:
        up_read(&v9ses->rename_sem);
        return fid;
}

/**
 * v9fs_fid_lookup - lookup for a fid, try to walk if not found
 * @dentry: dentry to look for fid in
 *
 * Look for a fid in the specified dentry for the current user.
 * If no fid is found, try to create one walking from a fid from the parent
 * dentry (if it has one), or the root dentry. If the user haven't accessed
 * the fs yet, attach now and walk from the root.
 */

struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
{
        kuid_t uid;
        int  any, access;
        struct v9fs_session_info *v9ses;

        v9ses = v9fs_dentry2v9ses(dentry);
        access = v9ses->flags & V9FS_ACCESS_MASK;
        switch (access) {
        case V9FS_ACCESS_SINGLE:
        case V9FS_ACCESS_USER:
        case V9FS_ACCESS_CLIENT:
                uid = current_fsuid();
                any = 0;
                break;

        case V9FS_ACCESS_ANY:
                uid = v9ses->uid;
                any = 1;
                break;

        default:
                uid = INVALID_UID;
                any = 0;
                break;
        }
        return v9fs_fid_lookup_with_uid(dentry, uid, any);
}

struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
{
        int err;
        struct p9_fid *fid;

        fid = clone_fid(v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0));
        if (IS_ERR(fid))
                goto error_out;
        /*
         * writeback fid will only be used to write back the
         * dirty pages. We always request for the open fid in read-write
         * mode so that a partial page write which result in page
         * read can work.
         */
        err = p9_client_open(fid, O_RDWR);
        if (err < 0) {
                p9_client_clunk(fid);
                fid = ERR_PTR(err);
                goto error_out;
        }
error_out:
        return fid;
}