[PATCH v1 15/17] fuse: add passthrough setattr

[Joanne Koong <joannelkoong@gmail.com>]

Add passthrough setattr for setting the attributes directly on a
backing inode via notify_change() instead of issuing a FUSE_SETATTR
request to the server.

After updating the backing inode, sync the fuse inode's vfs-visible
attributes with a passthrough getattr (which is guaranteed to be
supported, as getattr must be passed through in order to use inode
passthrough) so that it matches the attributes of the backing file.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/fuse/dir.c             |  3 +++
 fs/fuse/fuse_i.h          |  3 ++-
 fs/fuse/passthrough.c     | 31 +++++++++++++++++++++++++++++++
 include/uapi/linux/fuse.h |  1 +
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index ff9a92d8a496..6dea0f8e384f 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -2546,6 +2546,9 @@ static int fuse_setattr(struct mnt_idmap *idmap, struct dentry *entry,
 	if (!attr->ia_valid)
 		return 0;
 
+	if (fuse_inode_passthrough_op(inode, FUSE_SETATTR))
+		return fuse_passthrough_setattr(inode, attr);
+
 	ret = fuse_do_setattr(idmap, entry, attr, file);
 	if (!ret) {
 		/*
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index daf7b664e1b9..d722382676e2 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1571,7 +1571,7 @@ void fuse_file_release(struct inode *inode, struct fuse_file *ff,
 
 /* Inode passthrough operations for backing file attached to inode */
 #define FUSE_PASSTHROUGH_INODE_OPS \
-	(FUSE_PASSTHROUGH_OP_GETATTR)
+	(FUSE_PASSTHROUGH_OP_GETATTR | FUSE_PASSTHROUGH_OP_SETATTR)
 
 #define FUSE_BACKING_MAP_OP(map, op) \
 	((map)->ops_mask & FUSE_PASSTHROUGH_OP(op))
@@ -1683,6 +1683,7 @@ static inline bool fuse_inode_passthrough_op(struct inode *inode,
 
 int fuse_passthrough_getattr(struct inode *inode, struct kstat *stat,
 			     u32 request_mask, unsigned int flags);
+int fuse_passthrough_setattr(struct inode *inode, struct iattr *attr);
 
 static inline bool fuse_use_entry2(struct fuse_conn *fc)
 {
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index 8ecce2a97ee8..c70478f07d6a 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -9,6 +9,7 @@
 
 #include <linux/file.h>
 #include <linux/backing-file.h>
+#include <linux/posix_acl.h>
 #include <linux/splice.h>
 
 static void fuse_file_accessed(struct file *file)
@@ -251,3 +252,33 @@ int fuse_passthrough_getattr(struct inode *inode, struct kstat *stat,
 
 	return 0;
 }
+
+int fuse_passthrough_setattr(struct inode *inode, struct iattr *attr)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_backing *fb = fuse_inode_passthrough(fi);
+	const struct cred *old_cred;
+	struct dentry *backing_entry = fb->file->f_path.dentry;
+	struct mnt_idmap *backing_idmap = mnt_idmap(fb->file->f_path.mnt);
+	int err;
+
+	old_cred = override_creds(fb->cred);
+	inode_lock(d_inode(backing_entry));
+	err = notify_change(backing_idmap, backing_entry, attr, NULL);
+	inode_unlock(d_inode(backing_entry));
+	revert_creds(old_cred);
+
+	if (err)
+		return err;
+
+	if (fc->posix_acl)
+		forget_all_cached_acls(inode);
+
+	/*
+	 * Sync the fuse inode's cached attributes with the backing inode after
+	 * updating the backing inode's attributes. The fuse inode's vfs-visible
+	 * fields need to be in sync with the backing inode
+	 */
+	return fuse_passthrough_getattr(inode, NULL, STATX_BASIC_STATS, 0);
+}
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 3963631558f9..040fee549bb9 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -1158,6 +1158,7 @@ struct fuse_backing_map {
 #define FUSE_PASSTHROUGH_OP_WRITE	FUSE_PASSTHROUGH_OP(FUSE_WRITE)
 #define FUSE_PASSTHROUGH_OP_READDIR	FUSE_PASSTHROUGH_OP(FUSE_READDIR)
 #define FUSE_PASSTHROUGH_OP_GETATTR	FUSE_PASSTHROUGH_OP(FUSE_GETATTR)
+#define FUSE_PASSTHROUGH_OP_SETATTR	FUSE_PASSTHROUGH_OP(FUSE_SETATTR)
 
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
-- 
2.52.0