/*
 * Copyright (C) Neil Brown 2002
 * Copyright (C) Christoph Hellwig 2007
 *
 * This file contains the code mapping from inodes to NFS file handles,
 * and for mapping back from file handles to dentries.
 *
 * For details on why we do all the strange and hairy things in here
 * take a look at Documentation/filesystems/nfs/Exporting.
 */
#include <linux/exportfs.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/sched.h>

#define dprintk(fmt, args...) do{}while(0)


static int get_name(const struct path *path, char *name, struct dentry *child);


static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
                char *name, struct dentry *child)
{
        const struct export_operations *nop = dir->d_sb->s_export_op;
        struct path path = {.mnt = mnt, .dentry = dir};

        if (nop->get_name)
                return nop->get_name(dir, name, child);
        else
                return get_name(&path, name, child);
}

/*
 * Check if the dentry or any of it's aliases is acceptable.
 */
static struct dentry *
find_acceptable_alias(struct dentry *result,
                int (*acceptable)(void *context, struct dentry *dentry),
                void *context)
{
        struct dentry *dentry, *toput = NULL;
        struct inode *inode;
        struct hlist_node *p;

        if (acceptable(context, result))
                return result;

        inode = result->d_inode;
        spin_lock(&inode->i_lock);
        hlist_for_each_entry(dentry, p, &inode->i_dentry, d_alias) {
                dget(dentry);
                spin_unlock(&inode->i_lock);
                if (toput)
                        dput(toput);
                if (dentry != result && acceptable(context, dentry)) {
                        dput(result);
                        return dentry;
                }
                spin_lock(&inode->i_lock);
                toput = dentry;
        }
        spin_unlock(&inode->i_lock);

        if (toput)
                dput(toput);
        return NULL;
}

/*
 * Find root of a disconnected subtree and return a reference to it.
 */
static struct dentry *
find_disconnected_root(struct dentry *dentry)
{
        dget(dentry);
        while (!IS_ROOT(dentry)) {
                struct dentry *parent = dget_parent(dentry);

                if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
                        dput(parent);
                        break;
                }

                dput(dentry);
                dentry = parent;
        }
        return dentry;
}

/*
 * Make sure target_dir is fully connected to the dentry tree.
 *
 * It may already be, as the flag isn't always updated when connection happens.
 */
static int
reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
{
        int noprogress = 0;
        int err = -ESTALE;

        /*
         * It is possible that a confused file system might not let us complete
         * the path to the root.  For example, if get_parent returns a directory
         * in which we cannot find a name for the child.  While this implies a
         * very sick filesystem we don't want it to cause knfsd to spin.  Hence
         * the noprogress counter.  If we go through the loop 10 times (2 is
         * probably enough) without getting anywhere, we just give up
         */
        while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
                struct dentry *pd = find_disconnected_root(target_dir);

                if (!IS_ROOT(pd)) {
                        /* must have found a connected parent - great */
                        spin_lock(&pd->d_lock);
                        pd->d_flags &= ~DCACHE_DISCONNECTED;
                        spin_unlock(&pd->d_lock);
                        noprogress = 0;
                } else if (pd == mnt->mnt_sb->s_root) {
                        printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
                        spin_lock(&pd->d_lock);
                        pd->d_flags &= ~DCACHE_DISCONNECTED;
                        spin_unlock(&pd->d_lock);
                        noprogress = 0;
                } else {
                        /*
                         * We have hit the top of a disconnected path, try to
                         * find parent and connect.
                         *
                         * Racing with some other process renaming a directory
                         * isn't much of a problem here.  If someone renames
                         * the directory, it will end up properly connected,
                         * which is what we want
                         *
                         * Getting the parent can't be supported generically,
                         * the locking is too icky.
                         *
                         * Instead we just return EACCES.  If server reboots
                         * or inodes get flushed, you lose
                         */
                        struct dentry *ppd = ERR_PTR(-EACCES);
                        struct dentry *npd;

                        mutex_lock(&pd->d_inode->i_mutex);
                        if (mnt->mnt_sb->s_export_op->get_parent)
                                ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
                        mutex_unlock(&pd->d_inode->i_mutex);

                        if (IS_ERR(ppd)) {
                                err = PTR_ERR(ppd);
                                dprintk("%s: get_parent of %ld failed, err %d\n",
                                        __func__, pd->d_inode->i_ino, err);
                                dput(pd);
                                break;
                        }

                        dprintk("%s: find name of %lu in %lu\n", __func__,
                                pd->d_inode->i_ino, ppd->d_inode->i_ino);
                        err = exportfs_get_name(mnt, ppd, nbuf, pd);
                        if (err) {
                                dput(ppd);
                                dput(pd);
                                if (err == -ENOENT)
                                        /* some race between get_parent and
                                         * get_name?  just try again
                                         */
                                        continue;
                                break;
                        }
                        dprintk("%s: found name: %s\n", __func__, nbuf);
                        mutex_lock(&ppd->d_inode->i_mutex);
                        npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
                        mutex_unlock(&ppd->d_inode->i_mutex);
                        if (IS_ERR(npd)) {
                                err = PTR_ERR(npd);
                                dprintk("%s: lookup failed: %d\n",
                                        __func__, err);
                                dput(ppd);
                                dput(pd);
                                break;
                        }
                        /* we didn't really want npd, we really wanted
                         * a side-effect of the lookup.
                         * hopefully, npd == pd, though it isn't really
                         * a problem if it isn't
                         */
                        if (npd == pd)
                                noprogress = 0;
                        else
                                printk("%s: npd != pd\n", __func__);
                        dput(npd);
                        dput(ppd);
                        if (IS_ROOT(pd)) {
                                /* something went wrong, we have to give up */
                                dput(pd);
                                break;
                        }
                }
                dput(pd);
        }

        if (target_dir->d_flags & DCACHE_DISCONNECTED) {
                /* something went wrong - oh-well */
                if (!err)
                        err = -ESTALE;
                return err;
        }

        return 0;
}

struct getdents_callback {
        char *name;             /* name that was found. It already points to a
                                   buffer NAME_MAX+1 is size */
        unsigned long ino;      /* the inum we are looking for */
        int found;              /* inode matched? */
        int sequence;           /* sequence counter */
};

/*
 * A rather strange filldir function to capture
 * the name matching the specified inode number.
 */
static int filldir_one(void * __buf, const char * name, int len,
                        loff_t pos, u64 ino, unsigned int d_type)
{
        struct getdents_callback *buf = __buf;
        int result = 0;

        buf->sequence++;
        if (buf->ino == ino) {
                memcpy(buf->name, name, len);
                buf->name[len] = '\0';
                buf->found = 1;
                result = -1;
        }
        return result;
}

/**
 * get_name - default export_operations->get_name function
 * @dentry: the directory in which to find a name
 * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
 * @child:  the dentry for the child directory.
 *
 * calls readdir on the parent until it finds an entry with
 * the same inode number as the child, and returns that.
 */
static int get_name(const struct path *path, char *name, struct dentry *child)
{
        const struct cred *cred = current_cred();
        struct inode *dir = path->dentry->d_inode;
        int error;
        struct file *file;
        struct getdents_callback buffer;

        error = -ENOTDIR;
        if (!dir || !S_ISDIR(dir->i_mode))
                goto out;
        error = -EINVAL;
        if (!dir->i_fop)
                goto out;
        /*
         * Open the directory ...
         */
        file = dentry_open(path, O_RDONLY, cred);
        error = PTR_ERR(file);
        if (IS_ERR(file))
                goto out;

        error = -EINVAL;
        if (!file->f_op->readdir)
                goto out_close;

        buffer.name = name;
        buffer.ino = child->d_inode->i_ino;
        buffer.found = 0;
        buffer.sequence = 0;
        while (1) {
                int old_seq = buffer.sequence;

                error = vfs_readdir(file, filldir_one, &buffer);
                if (buffer.found) {
                        error = 0;
                        break;
                }

                if (error < 0)
                        break;

                error = -ENOENT;
                if (old_seq == buffer.sequence)
                        break;
        }

out_close:
        fput(file);
out:
        return error;
}

/**
 * export_encode_fh - default export_operations->encode_fh function
 * @inode:   the object to encode
 * @fh:      where to store the file handle fragment
 * @max_len: maximum length to store there
 * @parent:  parent directory inode, if wanted
 *
 * This default encode_fh function assumes that the 32 inode number
 * is suitable for locating an inode, and that the generation number
 * can be used to check that it is still valid.  It places them in the
 * filehandle fragment where export_decode_fh expects to find them.
 */
static int export_encode_fh(struct inode *inode, struct fid *fid,
                int *max_len, struct inode *parent)
{
        int len = *max_len;
        int type = FILEID_INO32_GEN;

        if (parent && (len < 4)) {
                *max_len = 4;
                return 255;
        } else if (len < 2) {
                *max_len = 2;
                return 255;
        }

        len = 2;
        fid->i32.ino = inode->i_ino;
        fid->i32.gen = inode->i_generation;
        if (parent) {
                fid->i32.parent_ino = parent->i_ino;
                fid->i32.parent_gen = parent->i_generation;
                len = 4;
                type = FILEID_INO32_GEN_PARENT;
        }
        *max_len = len;
        return type;
}

int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
                int connectable)
{
        const struct export_operations *nop = dentry->d_sb->s_export_op;
        int error;
        struct dentry *p = NULL;
        struct inode *inode = dentry->d_inode, *parent = NULL;

        if (connectable && !S_ISDIR(inode->i_mode)) {
                p = dget_parent(dentry);
                /*
                 * note that while p might've ceased to be our parent already,
                 * it's still pinned by and still positive.
                 */
                parent = p->d_inode;
        }
        if (nop->encode_fh)
                error = nop->encode_fh(inode, fid->raw, max_len, parent);
        else
                error = export_encode_fh(inode, fid, max_len, parent);
        dput(p);

        return error;
}
EXPORT_SYMBOL_GPL(exportfs_encode_fh);

struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
                int fh_len, int fileid_type,
                int (*acceptable)(void *, struct dentry *), void *context)
{
        const struct export_operations *nop = mnt->mnt_sb->s_export_op;
        struct dentry *result, *alias;
        char nbuf[NAME_MAX+1];
        int err;

        /*
         * Try to get any dentry for the given file handle from the filesystem.
         */
        if (!nop || !nop->fh_to_dentry)
                return ERR_PTR(-ESTALE);
        result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
        if (!result)
                result = ERR_PTR(-ESTALE);
        if (IS_ERR(result))
                return result;

        if (S_ISDIR(result->d_inode->i_mode)) {
                /*
                 * This request is for a directory.
                 *
                 * On the positive side there is only one dentry for each
                 * directory inode.  On the negative side this implies that we
                 * to ensure our dentry is connected all the way up to the
                 * filesystem root.
                 */
                if (result->d_flags & DCACHE_DISCONNECTED) {
                        err = reconnect_path(mnt, result, nbuf);
                        if (err)
                                goto err_result;
                }

                if (!acceptable(context, result)) {
                        err = -EACCES;
                        goto err_result;
                }

                return result;
        } else {
                /*
                 * It's not a directory.  Life is a little more complicated.
                 */
                struct dentry *target_dir, *nresult;

                /*
                 * See if either the dentry we just got from the filesystem
                 * or any alias for it is acceptable.  This is always true
                 * if this filesystem is exported without the subtreecheck
                 * option.  If the filesystem is exported with the subtree
                 * check option there's a fair chance we need to look at
                 * the parent directory in the file handle and make sure
                 * it's connected to the filesystem root.
                 */
                alias = find_acceptable_alias(result, acceptable, context);
                if (alias)
                        return alias;

                /*
                 * Try to extract a dentry for the parent directory from the
                 * file handle.  If this fails we'll have to give up.
                 */
                err = -ESTALE;
                if (!nop->fh_to_parent)
                        goto err_result;

                target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
                                fh_len, fileid_type);
                if (!target_dir)
                        goto err_result;
                err = PTR_ERR(target_dir);
                if (IS_ERR(target_dir))
                        goto err_result;

                /*
                 * And as usual we need to make sure the parent directory is
                 * connected to the filesystem root.  The VFS really doesn't
                 * like disconnected directories..
                 */
                err = reconnect_path(mnt, target_dir, nbuf);
                if (err) {
                        dput(target_dir);
                        goto err_result;
                }

                /*
                 * 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) {
                        mutex_lock(&target_dir->d_inode->i_mutex);
                        nresult = lookup_one_len(nbuf, target_dir,
                                                 strlen(nbuf));
                        mutex_unlock(&target_dir->d_inode->i_mutex);
                        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);
        return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(exportfs_decode_fh);

MODULE_LICENSE("GPL");