Fixed MTP to work with TWRP

fs/exportfs/Makefile

@@ -0,0 +1,6 @@
+#
+# Makefile for the filesystem export support routines.
+
+obj-$(CONFIG_EXPORTFS) += exportfs.o
+
+exportfs-objs := expfs.o

fs/exportfs/expfs.c

@@ -0,0 +1,543 @@
+/*
+ * 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;
+
+	if (acceptable(context, result))
+		return result;
+
+	inode = result->d_inode;
+	spin_lock(&inode->i_lock);
+	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.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;
+}
+
+static bool dentry_connected(struct dentry *dentry)
+{
+	dget(dentry);
+	while (dentry->d_flags & DCACHE_DISCONNECTED) {
+		struct dentry *parent = dget_parent(dentry);
+
+		dput(dentry);
+		if (IS_ROOT(dentry)) {
+			dput(parent);
+			return false;
+		}
+		dentry = parent;
+	}
+	dput(dentry);
+	return true;
+}
+
+static void clear_disconnected(struct dentry *dentry)
+{
+	dget(dentry);
+	while (dentry->d_flags & DCACHE_DISCONNECTED) {
+		struct dentry *parent = dget_parent(dentry);
+
+		WARN_ON_ONCE(IS_ROOT(dentry));
+
+		spin_lock(&dentry->d_lock);
+		dentry->d_flags &= ~DCACHE_DISCONNECTED;
+		spin_unlock(&dentry->d_lock);
+
+		dput(dentry);
+		dentry = parent;
+	}
+	dput(dentry);
+}
+
+/*
+ * Reconnect a directory dentry with its parent.
+ *
+ * This can return a dentry, or NULL, or an error.
+ *
+ * In the first case the returned dentry is the parent of the given
+ * dentry, and may itself need to be reconnected to its parent.
+ *
+ * In the NULL case, a concurrent VFS operation has either renamed or
+ * removed this directory.  The concurrent operation has reconnected our
+ * dentry, so we no longer need to.
+ */
+static struct dentry *reconnect_one(struct vfsmount *mnt,
+		struct dentry *dentry, char *nbuf)
+{
+	struct dentry *parent;
+	struct dentry *tmp;
+	int err;
+
+	parent = ERR_PTR(-EACCES);
+	mutex_lock(&dentry->d_inode->i_mutex);
+	if (mnt->mnt_sb->s_export_op->get_parent)
+		parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
+	mutex_unlock(&dentry->d_inode->i_mutex);
+
+	if (IS_ERR(parent)) {
+		dprintk("%s: get_parent of %ld failed, err %d\n",
+			__func__, dentry->d_inode->i_ino, PTR_ERR(parent));
+		return parent;
+	}
+
+	dprintk("%s: find name of %lu in %lu\n", __func__,
+		dentry->d_inode->i_ino, parent->d_inode->i_ino);
+	err = exportfs_get_name(mnt, parent, nbuf, dentry);
+	if (err == -ENOENT)
+		goto out_reconnected;
+	if (err)
+		goto out_err;
+	dprintk("%s: found name: %s\n", __func__, nbuf);
+	mutex_lock(&parent->d_inode->i_mutex);
+	tmp = lookup_one_len(nbuf, parent, strlen(nbuf));
+	mutex_unlock(&parent->d_inode->i_mutex);
+	if (IS_ERR(tmp)) {
+		dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
+		goto out_err;
+	}
+	if (tmp != dentry) {
+		dput(tmp);
+		goto out_reconnected;
+	}
+	dput(tmp);
+	if (IS_ROOT(dentry)) {
+		err = -ESTALE;
+		goto out_err;
+	}
+	return parent;
+
+out_err:
+	dput(parent);
+	return ERR_PTR(err);
+out_reconnected:
+	dput(parent);
+	/*
+	 * Someone must have renamed our entry into another parent, in
+	 * which case it has been reconnected by the rename.
+	 *
+	 * Or someone removed it entirely, in which case filehandle
+	 * lookup will succeed but the directory is now IS_DEAD and
+	 * subsequent operations on it will fail.
+	 *
+	 * Alternatively, maybe there was no race at all, and the
+	 * filesystem is just corrupt and gave us a parent that doesn't
+	 * actually contain any entry pointing to this inode.  So,
+	 * double check that this worked and return -ESTALE if not:
+	 */
+	if (!dentry_connected(dentry))
+		return ERR_PTR(-ESTALE);
+	return NULL;
+}
+
+/*
+ * Make sure target_dir is fully connected to the dentry tree.
+ *
+ * On successful return, DCACHE_DISCONNECTED will be cleared on
+ * target_dir, and target_dir->d_parent->...->d_parent will reach the
+ * root of the filesystem.
+ *
+ * Whenever DCACHE_DISCONNECTED is unset, target_dir is fully connected.
+ * But the converse is not true: target_dir may have DCACHE_DISCONNECTED
+ * set but already be connected.  In that case we'll verify the
+ * connection to root and then clear the flag.
+ *
+ * Note that target_dir could be removed by a concurrent operation.  In
+ * that case reconnect_path may still succeed with target_dir fully
+ * connected, but further operations using the filehandle will fail when
+ * necessary (due to S_DEAD being set on the directory).
+ */
+static int
+reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
+{
+	struct dentry *dentry, *parent;
+
+	dentry = dget(target_dir);
+
+	while (dentry->d_flags & DCACHE_DISCONNECTED) {
+		BUG_ON(dentry == mnt->mnt_sb->s_root);
+
+		if (IS_ROOT(dentry))
+			parent = reconnect_one(mnt, dentry, nbuf);
+		else
+			parent = dget_parent(dentry);
+
+		if (!parent)
+			break;
+		dput(dentry);
+		if (IS_ERR(parent))
+			return PTR_ERR(parent);
+		dentry = parent;
+	}
+	dput(dentry);
+	clear_disconnected(target_dir);
+	return 0;
+}
+
+struct getdents_callback {
+	struct dir_context ctx;
+	char *name;		/* name that was found. It already points to a
+				   buffer NAME_MAX+1 is size */
+	u64 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 && len <= NAME_MAX) {
+		memcpy(buf->name, name, len);
+		buf->name[len] = '\0';
+		buf->found = 1;
+		result = -1;
+	}
+	return result;
+}
+
+/**
+ * get_name - default export_operations->get_name function
+ * @path:   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 kstat stat;
+	struct path child_path = {
+		.mnt = path->mnt,
+		.dentry = child,
+	};
+	struct getdents_callback buffer = {
+		.ctx.actor = filldir_one,
+		.name = name,
+	};
+
+	error = -ENOTDIR;
+	if (!dir || !S_ISDIR(dir->i_mode))
+		goto out;
+	error = -EINVAL;
+	if (!dir->i_fop)
+		goto out;
+	/*
+	 * inode->i_ino is unsigned long, kstat->ino is u64, so the
+	 * former would be insufficient on 32-bit hosts when the
+	 * filesystem supports 64-bit inode numbers.  So we need to
+	 * actually call ->getattr, not just read i_ino:
+	 */
+	error = vfs_getattr_nosec(&child_path, &stat);
+	if (error)
+		return error;
+	buffer.ino = stat.ino;
+	/*
+	 * 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->iterate)
+		goto out_close;
+
+	buffer.sequence = 0;
+	while (1) {
+		int old_seq = buffer.sequence;
+
+		error = iterate_dir(file, &buffer.ctx);
+		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
+ * @fid:     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 FILEID_INVALID;
+	} else if (len < 2) {
+		*max_len = 2;
+		return FILEID_INVALID;
+	}
+
+	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_inode_fh(struct inode *inode, struct fid *fid,
+			     int *max_len, struct inode *parent)
+{
+	const struct export_operations *nop = inode->i_sb->s_export_op;
+
+	if (nop && nop->encode_fh)
+		return nop->encode_fh(inode, fid->raw, max_len, parent);
+
+	return export_encode_fh(inode, fid, max_len, parent);
+}
+EXPORT_SYMBOL_GPL(exportfs_encode_inode_fh);
+
+int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
+		int connectable)
+{
+	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;
+	}
+
+	error = exportfs_encode_inode_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");