afs: Implement sillyrename for unlink and rename

Implement sillyrename for AFS unlink and rename, using the NFS variant
implementation as a basis.

Note that the asynchronous file locking extender/releaser has to be
notified with a state change to stop it complaining if there's a race
between that and the actual file deletion.

A tracepoint, afs_silly_rename, is also added to note the silly rename and
the cleanup.  The afs_edit_dir tracepoint is given some extra reason
indicators and the afs_flock_ev tracepoint is given a silly-delete file
lock cancellation indicator.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 239 insertions, 0 deletions

diff --git a/fs/afs/dir_silly.c b/fs/afs/dir_silly.c
new file mode 100644
index 000000000000..f6f89fdab6b2
--- /dev/null
+++ b/fs/afs/dir_silly.c
@@ -0,0 +1,239 @@
+/* AFS silly rename handling
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ * - Derived from NFS's sillyrename.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/fsnotify.h>
+#include "internal.h"
+
+/*
+ * Actually perform the silly rename step.
+ */
+static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode,
+			       struct dentry *old, struct dentry *new,
+			       struct key *key)
+{
+	struct afs_fs_cursor fc;
+	u64 dir_data_version = dvnode->status.data_version;
+	int ret = -ERESTARTSYS;
+
+	_enter("%pd,%pd", old, new);
+
+	trace_afs_silly_rename(vnode, false);
+	if (afs_begin_vnode_operation(&fc, dvnode, key)) {
+		while (afs_select_fileserver(&fc)) {
+			fc.cb_break = afs_calc_vnode_cb_break(dvnode);
+			afs_fs_rename(&fc, old->d_name.name,
+				      dvnode, new->d_name.name,
+				      dir_data_version, dir_data_version);
+		}
+
+		afs_vnode_commit_status(&fc, dvnode, fc.cb_break);
+		ret = afs_end_vnode_operation(&fc);
+	}
+
+	if (ret == 0) {
+		spin_lock(&old->d_lock);
+		old->d_flags |= DCACHE_NFSFS_RENAMED;
+		spin_unlock(&old->d_lock);
+		if (dvnode->silly_key != key) {
+			key_put(dvnode->silly_key);
+			dvnode->silly_key = key_get(key);
+		}
+
+		if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
+			afs_edit_dir_remove(dvnode, &old->d_name,
+					    afs_edit_dir_for_silly_0);
+		if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
+			afs_edit_dir_add(dvnode, &new->d_name,
+					 &vnode->fid, afs_edit_dir_for_silly_1);
+
+		/* vfs_unlink and the like do not issue this when a file is
+		 * sillyrenamed, so do it here.
+		 */
+		fsnotify_nameremove(old, 0);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/**
+ * afs_sillyrename - Perform a silly-rename of a dentry
+ *
+ * AFS is stateless and the server doesn't know when the client is holding a
+ * file open.  To prevent application problems when a file is unlinked while
+ * it's still open, the client performs a "silly-rename".  That is, it renames
+ * the file to a hidden file in the same directory, and only performs the
+ * unlink once the last reference to it is put.
+ *
+ * The final cleanup is done during dentry_iput.
+ */
+int afs_sillyrename(struct afs_vnode *dvnode, struct afs_vnode *vnode,
+		    struct dentry *dentry, struct key *key)
+{
+	static unsigned int sillycounter;
+	struct dentry *sdentry = NULL;
+	unsigned char silly[16];
+	int ret = -EBUSY;
+
+	_enter("");
+
+	/* We don't allow a dentry to be silly-renamed twice. */
+	if (dentry->d_flags & DCACHE_NFSFS_RENAMED)
+		return -EBUSY;
+
+	sdentry = NULL;
+	do {
+		int slen;
+
+		dput(sdentry);
+		sillycounter++;
+
+		/* Create a silly name.  Note that the ".__afs" prefix is
+		 * understood by the salvager and must not be changed.
+		 */
+		slen = scnprintf(silly, sizeof(silly), ".__afs%04X", sillycounter);
+		sdentry = lookup_one_len(silly, dentry->d_parent, slen);
+
+		/* N.B. Better to return EBUSY here ... it could be dangerous
+		 * to delete the file while it's in use.
+		 */
+		if (IS_ERR(sdentry))
+			goto out;
+	} while (!d_is_negative(sdentry));
+
+	ihold(&vnode->vfs_inode);
+
+	ret = afs_do_silly_rename(dvnode, vnode, dentry, sdentry, key);
+	switch (ret) {
+	case 0:
+		/* The rename succeeded. */
+		d_move(dentry, sdentry);
+		break;
+	case -ERESTARTSYS:
+		/* The result of the rename is unknown. Play it safe by forcing
+		 * a new lookup.
+		 */
+		d_drop(dentry);
+		d_drop(sdentry);
+	}
+
+	iput(&vnode->vfs_inode);
+	dput(sdentry);
+out:
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Tell the server to remove a sillyrename file.
+ */
+static int afs_do_silly_unlink(struct afs_vnode *dvnode, struct afs_vnode *vnode,
+			       struct dentry *dentry, struct key *key)
+{
+	struct afs_fs_cursor fc;
+	u64 dir_data_version = dvnode->status.data_version;
+	int ret = -ERESTARTSYS;
+
+	_enter("");
+
+	trace_afs_silly_rename(vnode, true);
+	if (afs_begin_vnode_operation(&fc, dvnode, key)) {
+		while (afs_select_fileserver(&fc)) {
+			fc.cb_break = afs_calc_vnode_cb_break(dvnode);
+
+			if (test_bit(AFS_SERVER_FL_IS_YFS, &fc.cbi->server->flags) &&
+			    !test_bit(AFS_SERVER_FL_NO_RM2, &fc.cbi->server->flags)) {
+				yfs_fs_remove_file2(&fc, vnode, dentry->d_name.name,
+						    dir_data_version);
+				if (fc.ac.error != -ECONNABORTED ||
+				    fc.ac.abort_code != RXGEN_OPCODE)
+					continue;
+				set_bit(AFS_SERVER_FL_NO_RM2, &fc.cbi->server->flags);
+			}
+
+			afs_fs_remove(&fc, vnode, dentry->d_name.name, false,
+				      dir_data_version);
+		}
+
+		afs_vnode_commit_status(&fc, dvnode, fc.cb_break);
+		ret = afs_end_vnode_operation(&fc);
+		if (ret == 0) {
+			drop_nlink(&vnode->vfs_inode);
+			if (vnode->vfs_inode.i_nlink == 0) {
+				set_bit(AFS_VNODE_DELETED, &vnode->flags);
+				clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
+			}
+		}
+		if (ret == 0 &&
+		    test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
+			afs_edit_dir_remove(dvnode, &dentry->d_name,
+					    afs_edit_dir_for_unlink);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Remove sillyrename file on iput.
+ */
+int afs_silly_iput(struct dentry *dentry, struct inode *inode)
+{
+	struct afs_vnode *dvnode = AFS_FS_I(d_inode(dentry->d_parent));
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct dentry *alias;
+	int ret;
+
+	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
+
+	_enter("%p{%pd},%llx", dentry, dentry, vnode->fid.vnode);
+
+	down_read(&dvnode->rmdir_lock);
+
+	alias = d_alloc_parallel(dentry->d_parent, &dentry->d_name, &wq);
+	if (IS_ERR(alias)) {
+		up_read(&dvnode->rmdir_lock);
+		return 0;
+	}
+
+	if (!d_in_lookup(alias)) {
+		/* We raced with lookup...  See if we need to transfer the
+		 * sillyrename information to the aliased dentry.
+		 */
+		ret = 0;
+		spin_lock(&alias->d_lock);
+		if (d_really_is_positive(alias) &&
+		    !(alias->d_flags & DCACHE_NFSFS_RENAMED)) {
+			alias->d_flags |= DCACHE_NFSFS_RENAMED;
+			ret = 1;
+		}
+		spin_unlock(&alias->d_lock);
+		up_read(&dvnode->rmdir_lock);
+		dput(alias);
+		return ret;
+	}
+
+	/* Stop lock-release from complaining. */
+	spin_lock(&vnode->lock);
+	vnode->lock_state = AFS_VNODE_LOCK_DELETED;
+	trace_afs_flock_ev(vnode, NULL, afs_flock_silly_delete, 0);
+	spin_unlock(&vnode->lock);
+
+	afs_do_silly_unlink(dvnode, vnode, dentry, dvnode->silly_key);
+	up_read(&dvnode->rmdir_lock);
+	d_lookup_done(alias);
+	dput(alias);
+	return 1;
+}