[PATCH 2/2] fuse: Add passthrough for mkdir and rmdir (WIP)

[Paul Lawrence <paullawrence@google.com>]

As proof of concept of setting a backing file at lookup, implement mkdir
and rmdir which work off the nodeid only and do not open the file.

Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 fs/fuse/dir.c             |  8 +++++++-
 fs/fuse/fuse_i.h          | 11 +++++++++--
 fs/fuse/passthrough.c     | 38 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/fuse.h |  2 ++
 4 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index c0bef93dd078..25d6929d600a 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -129,7 +129,7 @@ void fuse_invalidate_attr(struct inode *inode)
 	fuse_invalidate_attr_mask(inode, STATX_BASIC_STATS);
 }
 
-static void fuse_dir_changed(struct inode *dir)
+void fuse_dir_changed(struct inode *dir)
 {
 	fuse_invalidate_attr(dir);
 	inode_maybe_inc_iversion(dir, false);
@@ -951,6 +951,9 @@ static struct dentry *fuse_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (!fm->fc->dont_mask)
 		mode &= ~current_umask();
 
+	if (fuse_inode_passthrough_op(dir, FUSE_MKDIR))
+		return fuse_passthrough_mkdir(idmap, dir, entry, mode);
+
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.mode = mode;
 	inarg.umask = current_umask();
@@ -1058,6 +1061,9 @@ static int fuse_rmdir(struct inode *dir, struct dentry *entry)
 	if (fuse_is_bad(dir))
 		return -EIO;
 
+	if (fuse_inode_passthrough_op(dir, FUSE_RMDIR))
+		return fuse_passthrough_rmdir(dir, entry);
+
 	args.opcode = FUSE_RMDIR;
 	args.nodeid = get_node_id(dir);
 	args.in_numargs = 2;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index aebd338751f1..d8df2d5a73ac 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1279,6 +1279,7 @@ void fuse_check_timeout(struct work_struct *work);
 #define FUSE_STATX_MODSIZE	(FUSE_STATX_MODIFY | STATX_SIZE)
 
 void fuse_invalidate_attr(struct inode *inode);
+void fuse_dir_changed(struct inode *dir);
 void fuse_invalidate_attr_mask(struct inode *inode, u32 mask);
 
 void fuse_invalidate_entry_cache(struct dentry *entry);
@@ -1521,7 +1522,8 @@ void fuse_file_release(struct inode *inode, struct fuse_file *ff,
 
 /* Passthrough operations for directories */
 #define FUSE_PASSTHROUGH_DIR_OPS \
-	(FUSE_PASSTHROUGH_OP_READDIR)
+	(FUSE_PASSTHROUGH_OP_READDIR | FUSE_PASSTHROUGH_OP_MKDIR | \
+	 FUSE_PASSTHROUGH_OP_RMDIR)
 
 /* Inode passthrough operations for backing file attached to inode */
 #define FUSE_PASSTHROUGH_INODE_OPS \
@@ -1532,7 +1534,8 @@ void fuse_file_release(struct inode *inode, struct fuse_file *ff,
 	((map)->ops_mask & FUSE_PASSTHROUGH_OP(op))
 
 #define FUSE_BACKING_MAP_VALID_OPS \
-	(FUSE_PASSTHROUGH_RW_OPS | FUSE_PASSTHROUGH_INODE_OPS)
+	(FUSE_PASSTHROUGH_RW_OPS | FUSE_PASSTHROUGH_INODE_OPS |\
+	 FUSE_PASSTHROUGH_DIR_OPS)
 
 static inline struct fuse_backing *fuse_inode_backing(struct fuse_inode *fi)
 {
@@ -1626,6 +1629,10 @@ ssize_t fuse_passthrough_getxattr(struct inode *inode, const char *name,
 				  void *value, size_t size);
 ssize_t fuse_passthrough_listxattr(struct dentry *entry, char *list,
 				   size_t size);
+struct dentry *fuse_passthrough_mkdir(struct mnt_idmap *idmap,
+				      struct inode *dir, struct dentry *entry,
+				      umode_t mode);
+int fuse_passthrough_rmdir(struct inode *dir, struct dentry *entry);
 
 #ifdef CONFIG_SYSCTL
 extern int fuse_sysctl_register(void);
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index cee40e1c6e4a..acb06fbbd828 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -7,6 +7,7 @@
 
 #include "fuse_i.h"
 
+#include "linux/namei.h"
 #include <linux/file.h>
 #include <linux/backing-file.h>
 #include <linux/splice.h>
@@ -497,3 +498,40 @@ ssize_t fuse_passthrough_listxattr(struct dentry *entry, char *list,
 	revert_creds(old_cred);
 	return res;
 }
+
+struct dentry *fuse_passthrough_mkdir(struct mnt_idmap *idmap,
+				      struct inode *dir, struct dentry *entry,
+				      umode_t mode)
+{
+	struct fuse_backing *fb = fuse_inode_backing(get_fuse_inode(dir));
+	struct dentry *backing_entry, *new_entry;
+	const struct cred *old_cred;
+
+	old_cred = override_creds(fb->cred);
+	backing_entry = lookup_one_unlocked(idmap, &entry->d_name,
+		fb->file->f_path.dentry);
+	new_entry = vfs_mkdir(idmap, fb->file->f_inode, backing_entry, mode);
+	d_drop(entry);
+	revert_creds(old_cred);
+	fuse_dir_changed(dir);
+	return new_entry;
+}
+
+int fuse_passthrough_rmdir(struct inode *dir, struct dentry *entry)
+{
+	int err;
+	struct dentry *backing_entry;
+	struct fuse_backing *fb = fuse_inode_backing(get_fuse_inode(dir));
+	const struct cred *old_cred;
+
+	old_cred = override_creds(fb->cred);
+	backing_entry = lookup_one_unlocked(&nop_mnt_idmap, &entry->d_name,
+		fb->file->f_path.dentry);
+	err = vfs_rmdir(&nop_mnt_idmap, fb->file->f_inode, backing_entry);
+	dput(backing_entry);
+	if (!err)
+		d_drop(entry);
+	revert_creds(old_cred);
+	return err;
+}
+
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 6dbb045c794d..8181d07b7bf1 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -1135,6 +1135,8 @@ struct fuse_backing_map {
 #define FUSE_PASSTHROUGH_OP_STATX	FUSE_PASSTHROUGH_OP(FUSE_STATX)
 #define FUSE_PASSTHROUGH_OP_GETXATTR	FUSE_PASSTHROUGH_OP(FUSE_GETXATTR)
 #define FUSE_PASSTHROUGH_OP_LISTXATTR	FUSE_PASSTHROUGH_OP(FUSE_LISTXATTR)
+#define FUSE_PASSTHROUGH_OP_MKDIR	FUSE_PASSTHROUGH_OP(FUSE_MKDIR)
+#define FUSE_PASSTHROUGH_OP_RMDIR	FUSE_PASSTHROUGH_OP(FUSE_RMDIR)
 
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
-- 
2.50.1.565.gc32cd1483b-goog