[RFC PATCH v2 20/21] fuse-bpf: Add symlink/link support

[Daniel Rosenberg <drosen@google.com>]

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 fs/fuse/backing.c | 271 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/fuse/dir.c     |  11 ++
 fs/fuse/fuse_i.h  |  20 ++++
 3 files changed, 302 insertions(+)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 05fb88865289..a77414e8f3df 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -2319,6 +2319,104 @@ int fuse_bpf_unlink(int *out, struct inode *dir, struct dentry *entry)
 				dir, entry);
 }
 
+static int fuse_link_initialize_in(struct fuse_args *fa, struct fuse_link_in *fli,
+				   struct dentry *entry, struct inode *dir,
+				   struct dentry *newent)
+{
+	struct inode *src_inode = entry->d_inode;
+
+	*fli = (struct fuse_link_in) {
+		.oldnodeid = get_node_id(src_inode),
+	};
+
+	fa->opcode = FUSE_LINK;
+	fa->in_numargs = 2;
+	fa->in_args[0].size = sizeof(*fli);
+	fa->in_args[0].value = fli;
+	fa->in_args[1].size = newent->d_name.len + 1;
+	fa->in_args[1].value = (void *) newent->d_name.name;
+
+	return 0;
+}
+
+static int fuse_link_initialize_out(struct fuse_args *fa, struct fuse_link_in *fli,
+				    struct dentry *entry, struct inode *dir,
+				    struct dentry *newent)
+{
+	return 0;
+}
+
+static int fuse_link_backing(struct fuse_args *fa, int *out, struct dentry *entry,
+			     struct inode *dir, struct dentry *newent)
+{
+	struct path backing_old_path;
+	struct path backing_new_path;
+	struct dentry *backing_dir_dentry;
+	struct inode *fuse_new_inode = NULL;
+	struct fuse_inode *fuse_dir_inode = get_fuse_inode(dir);
+	struct inode *backing_dir_inode = fuse_dir_inode->backing_inode;
+
+	*out = 0;
+	get_fuse_backing_path(entry, &backing_old_path);
+	if (!backing_old_path.dentry)
+		return -EBADF;
+
+	get_fuse_backing_path(newent, &backing_new_path);
+	if (!backing_new_path.dentry) {
+		*out = -EBADF;
+		goto err_dst_path;
+	}
+
+	backing_dir_dentry = dget_parent(backing_new_path.dentry);
+	backing_dir_inode = d_inode(backing_dir_dentry);
+
+	inode_lock_nested(backing_dir_inode, I_MUTEX_PARENT);
+	*out = vfs_link(backing_old_path.dentry, &init_user_ns,
+		       backing_dir_inode, backing_new_path.dentry, NULL);
+	inode_unlock(backing_dir_inode);
+	if (*out)
+		goto out;
+
+	if (d_really_is_negative(backing_new_path.dentry) ||
+	    unlikely(d_unhashed(backing_new_path.dentry))) {
+		*out = -EINVAL;
+		/**
+		 * TODO: overlayfs responds to this situation with a
+		 * lookupOneLen. Should we do that too?
+		 */
+		goto out;
+	}
+
+	fuse_new_inode = fuse_iget_backing(dir->i_sb, fuse_dir_inode->nodeid, backing_dir_inode);
+	if (IS_ERR(fuse_new_inode)) {
+		*out = PTR_ERR(fuse_new_inode);
+		goto out;
+	}
+	d_instantiate(newent, fuse_new_inode);
+
+out:
+	dput(backing_dir_dentry);
+	path_put(&backing_new_path);
+err_dst_path:
+	path_put(&backing_old_path);
+	return *out;
+}
+
+static int fuse_link_finalize(struct fuse_args *fa, int *out, struct dentry *entry,
+			      struct inode *dir, struct dentry *newent)
+{
+	return 0;
+}
+
+int fuse_bpf_link(int *out, struct inode *inode, struct dentry *entry,
+		  struct inode *newdir, struct dentry *newent)
+{
+	return fuse_bpf_backing(inode, struct fuse_link_in, out,
+				fuse_link_initialize_in, fuse_link_initialize_out,
+				fuse_link_backing, fuse_link_finalize, entry,
+				newdir, newent);
+}
+
 struct fuse_getattr_io {
 	struct fuse_getattr_in fgi;
 	struct fuse_attr_out fao;
@@ -2600,6 +2698,179 @@ int fuse_bpf_statfs(int *out, struct inode *inode, struct dentry *dentry, struct
 				dentry, buf);
 }
 
+static int fuse_get_link_initialize_in(struct fuse_args *fa, struct fuse_unused_io *unused,
+				       struct inode *inode, struct dentry *dentry,
+				       struct delayed_call *callback)
+{
+	/*
+	 * TODO
+	 * If we want to handle changing these things, we'll need to copy
+	 * the lower fs's data into our own buffer, and provide our own callback
+	 * to free that buffer.
+	 *
+	 * Pre could change the name we're looking at
+	 * postfilter can change the name we return
+	 *
+	 * We ought to only make that buffer if it's been requested, so leaving
+	 * this unimplemented for the moment
+	 */
+	*fa = (struct fuse_args) {
+		.opcode = FUSE_READLINK,
+		.nodeid = get_node_id(inode),
+		.in_numargs = 1,
+		.in_args[0] = (struct fuse_in_arg) {
+			.size = dentry->d_name.len + 1,
+			.value =  (void *) dentry->d_name.name,
+		},
+		/*
+		 * .out_argvar = 1,
+		 * .out_numargs = 1,
+		 * .out_args[0].size = ,
+		 * .out_args[0].value = ,
+		 */
+	};
+
+	return 0;
+}
+
+static int fuse_get_link_initialize_out(struct fuse_args *fa, struct fuse_unused_io *unused,
+					struct inode *inode, struct dentry *dentry,
+					struct delayed_call *callback)
+{
+	/*
+	 * .out_argvar = 1,
+	 * .out_numargs = 1,
+	 * .out_args[0].size = ,
+	 * .out_args[0].value = ,
+	 */
+
+	return 0;
+}
+
+static int fuse_get_link_backing(struct fuse_args *fa, const char **out,
+				 struct inode *inode, struct dentry *dentry,
+				 struct delayed_call *callback)
+{
+	struct path backing_path;
+
+	if (!dentry) {
+		*out = ERR_PTR(-ECHILD);
+		return PTR_ERR(*out);
+	}
+
+	get_fuse_backing_path(dentry, &backing_path);
+	if (!backing_path.dentry) {
+		*out = ERR_PTR(-ECHILD);
+		return PTR_ERR(*out);
+	}
+
+	/*
+	 * TODO: If we want to do our own thing, copy the data and then call the
+	 * callback
+	 */
+	*out = vfs_get_link(backing_path.dentry, callback);
+
+	path_put(&backing_path);
+	return 0;
+}
+
+static int fuse_get_link_finalize(struct fuse_args *fa, const char **out,
+				  struct inode *inode, struct dentry *dentry,
+				  struct delayed_call *callback)
+{
+	return 0;
+}
+
+int fuse_bpf_get_link(const char **out, struct inode *inode, struct dentry *dentry,
+		      struct delayed_call *callback)
+{
+	return fuse_bpf_backing(inode, struct fuse_unused_io, out,
+				fuse_get_link_initialize_in, fuse_get_link_initialize_out,
+				fuse_get_link_backing,
+				fuse_get_link_finalize,
+				inode, dentry, callback);
+}
+
+static int fuse_symlink_initialize_in(struct fuse_args *fa, struct fuse_unused_io *unused,
+				      struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+	*fa = (struct fuse_args) {
+		.nodeid = get_node_id(dir),
+		.opcode = FUSE_SYMLINK,
+		.in_numargs = 2,
+		.in_args[0] = (struct fuse_in_arg) {
+			.size = entry->d_name.len + 1,
+			.value =  (void *) entry->d_name.name,
+		},
+		.in_args[1] = (struct fuse_in_arg) {
+			.size = len,
+			.value = (void *) link,
+		},
+	};
+
+	return 0;
+}
+
+static int fuse_symlink_initialize_out(struct fuse_args *fa, struct fuse_unused_io *unused,
+				       struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+	return 0;
+}
+
+static int fuse_symlink_backing(struct fuse_args *fa, int *out,
+				struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+	struct fuse_inode *fuse_inode = get_fuse_inode(dir);
+	struct inode *backing_inode = fuse_inode->backing_inode;
+	struct path backing_path;
+	struct inode *inode = NULL;
+
+	*out = 0;
+	//TODO Actually deal with changing the backing entry in symlink
+	get_fuse_backing_path(entry, &backing_path);
+	if (!backing_path.dentry)
+		return -EBADF;
+
+	inode_lock_nested(backing_inode, I_MUTEX_PARENT);
+	*out = vfs_symlink(&init_user_ns, backing_inode, backing_path.dentry,
+			  link);
+	inode_unlock(backing_inode);
+	if (*out)
+		goto out;
+	if (d_really_is_negative(backing_path.dentry) ||
+	    unlikely(d_unhashed(backing_path.dentry))) {
+		*out = -EINVAL;
+		/**
+		 * TODO: overlayfs responds to this situation with a
+		 * lookupOneLen. Should we do that too?
+		 */
+		goto out;
+	}
+	inode = fuse_iget_backing(dir->i_sb, fuse_inode->nodeid, backing_inode);
+	if (IS_ERR(inode)) {
+		*out = PTR_ERR(inode);
+		goto out;
+	}
+	d_instantiate(entry, inode);
+out:
+	path_put(&backing_path);
+	return *out;
+}
+
+static int  fuse_symlink_finalize(struct fuse_args *fa, int *out,
+				  struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+	return 0;
+}
+
+int  fuse_bpf_symlink(int *out, struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+	return fuse_bpf_backing(dir, struct fuse_unused_io, out,
+				fuse_symlink_initialize_in, fuse_symlink_initialize_out,
+				fuse_symlink_backing, fuse_symlink_finalize,
+				dir, entry, link, len);
+}
+
 struct fuse_read_io {
 	struct fuse_read_in fri;
 	struct fuse_read_out fro;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 899de6c84c2e..1f9105edc7e2 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -945,6 +945,10 @@ static int fuse_symlink(struct user_namespace *mnt_userns, struct inode *dir,
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	unsigned len = strlen(link) + 1;
 	FUSE_ARGS(args);
+	int err;
+
+	if (fuse_bpf_symlink(&err, dir, entry, link, len))
+		return err;
 
 	args.opcode = FUSE_SYMLINK;
 	args.in_numargs = 2;
@@ -1151,6 +1155,9 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
 	struct fuse_mount *fm = get_fuse_mount(inode);
 	FUSE_ARGS(args);
 
+	if (fuse_bpf_link(&err, inode, entry, newdir, newent))
+		return err;
+
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.oldnodeid = get_node_id(inode);
 	args.opcode = FUSE_LINK;
@@ -1543,12 +1550,16 @@ static const char *fuse_get_link(struct dentry *dentry, struct inode *inode,
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct page *page;
+	const char *out = NULL;
 	int err;
 
 	err = -EIO;
 	if (fuse_is_bad(inode))
 		goto out_err;
 
+	if (fuse_bpf_get_link(&out, inode, dentry, callback))
+		return out;
+
 	if (fc->cache_symlinks)
 		return page_get_link(dentry, inode, callback);
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 37b29a3ea330..99c9231ec98b 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1412,6 +1412,7 @@ int fuse_bpf_rename2(int *out, struct inode *olddir, struct dentry *oldent,
 int fuse_bpf_rename(int *out, struct inode *olddir, struct dentry *oldent,
 		    struct inode *newdir, struct dentry *newent);
 int fuse_bpf_unlink(int *out, struct inode *dir, struct dentry *entry);
+int fuse_bpf_link(int *out, struct inode *inode, struct dentry *entry, struct inode *dir, struct dentry *newent);
 int fuse_bpf_release(int *out, struct inode *inode, struct file *file);
 int fuse_bpf_releasedir(int *out, struct inode *inode, struct file *file);
 int fuse_bpf_flush(int *out, struct inode *inode, struct file *file, fl_owner_t id);
@@ -1436,6 +1437,9 @@ int fuse_bpf_getattr(int *out, struct inode *inode, const struct dentry *entry,
 		     u32 request_mask, unsigned int flags);
 int fuse_bpf_setattr(int *out, struct inode *inode, struct dentry *dentry, struct iattr *attr, struct file *file);
 int fuse_bpf_statfs(int *out, struct inode *inode, struct dentry *dentry, struct kstatfs *buf);
+int fuse_bpf_get_link(const char **out, struct inode *inode, struct dentry *dentry,
+		      struct delayed_call *callback);
+int fuse_bpf_symlink(int *out, struct inode *dir, struct dentry *entry, const char *link, int len);
 int fuse_bpf_readdir(int *out, struct inode *inode, struct file *file, struct dir_context *ctx);
 int fuse_bpf_access(int *out, struct inode *inode, int mask);
 
@@ -1485,6 +1489,11 @@ static inline int fuse_bpf_unlink(int *out, struct inode *dir, struct dentry *en
 	return 0;
 }
 
+static inline int fuse_bpf_link(int *out, struct inode *inode, struct dentry *entry, struct inode *dir, struct dentry *newent)
+{
+	return 0;
+}
+
 static inline int fuse_bpf_release(int *out, struct inode *inode, struct file *file)
 {
 	return 0;
@@ -1581,6 +1590,17 @@ static inline int fuse_bpf_statfs(int *out, struct inode *inode, struct dentry *
 	return 0;
 }
 
+static inline int fuse_bpf_get_link(const char **out, struct inode *inode, struct dentry *dentry,
+		      struct delayed_call *callback)
+{
+	return 0;
+}
+
+static inline int fuse_bpf_symlink(int *out, struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+	return 0;
+}
+
 static inline int fuse_bpf_readdir(int *out, struct inode *inode, struct file *file, struct dir_context *ctx)
 {
 	return 0;
-- 
2.38.1.584.g0f3c55d4c2-goog