[PATCH] fuse: Cache unsupported ioctl requests

[Stanislav Kinsburskii]

A server that does not implement FUSE_IOCTL returns -ENOSYS for each
request. Cache this response on the connection and return -ENOTTY for
subsequent ioctl requests without contacting the server.

Only cache request-level -ENOSYS. Errors in fuse_ioctl_out.result apply
to individual commands and must not disable ioctl support for the
connection.

Check the cached flag before preparing regular ioctl requests and before
opening a file for file-attribute ioctls, avoiding unnecessary allocations
and open/release requests.

Signed-off-by: Robet Byrnes <byrnes@xxxxxxxxxxxxxxx>
Signed-off-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxx>
---
 fs/fuse/fuse_i.h |  3 +++
 fs/fuse/ioctl.c  | 12 ++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 97d356588d00..e9d8b48069dd 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -720,6 +720,9 @@ struct fuse_conn {
 	/** @sync_init: Is synchronous FUSE_INIT allowed? */
 	unsigned int sync_init:1;
 
+	/** @no_ioctl: Is ioctl not implemented by fs? */
+	unsigned no_ioctl:1;
+
 	/** @max_stack_depth: Maximum stack depth for passthrough backing files */
 	int max_stack_depth;
 
diff --git a/fs/fuse/ioctl.c b/fs/fuse/ioctl.c
index dc3a188f5d72..3ae50a25064b 100644
--- a/fs/fuse/ioctl.c
+++ b/fs/fuse/ioctl.c
@@ -23,9 +23,11 @@ static ssize_t fuse_send_ioctl(struct fuse_mount *fm, struct fuse_args *args,
 
 	ret = fuse_simple_request(fm, args);
 
-	/* Translate ENOSYS, which shouldn't be returned from fs */
-	if (ret == -ENOSYS)
+	/* Cache request-level ENOSYS only; outarg->result is per-command. */
+	if (ret == -ENOSYS) {
+		fm->fc->no_ioctl = 1;
 		ret = -ENOTTY;
+	}
 
 	if (ret >= 0 && outarg->result == -ENOSYS)
 		outarg->result = -ENOTTY;
@@ -233,6 +235,9 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 	struct iov_iter ii;
 	struct fuse_args_pages ap = {};
 
+	if (fm->fc->no_ioctl)
+		return -ENOTTY;
+
 #if BITS_PER_LONG == 32
 	inarg.flags |= FUSE_IOCTL_32BIT;
 #else
@@ -492,6 +497,9 @@ static struct fuse_file *fuse_priv_ioctl_prepare(struct inode *inode)
 	if (!S_ISREG(inode->i_mode) && !isdir)
 		return ERR_PTR(-ENOTTY);
 
+	if (fm->fc->no_ioctl)
+		return ERR_PTR(-ENOTTY);
+
 	return fuse_file_open(fm, get_node_id(inode), O_RDONLY, isdir);
 }
 

---
base-commit: 68142f986ff04b2b70b31db00f719bf690f64a9a
change-id: 20260911-fuse-cache-no-ioctl-1bb573a27597

Best regards,
-- 
Stanislav Kinsburskii <skinsburskii@xxxxxxxxx>