[PATCH 3/8] fuse: capture the unique id of fuse commands being sent

Darrick J. Wong
2025-09-16T00:24:49Z

The fuse_request_{send,end} tracepoints capture the value of
req->in.h.unique in the trace output. It would be really nice if we
could use this to match a request to its response for debugging and
latency analysis, but the call to trace_fuse_request_send occurs before
the unique id has been set:

fuse_request_send: connection 8388608 req 0 opcode 1 (FUSE_LOOKUP) len 107
fuse_request_end: connection 8388608 req 6 len 16 error -2

(Notice that req moves from 0 to 6)

Move the callsites to trace_fuse_request_send to after the unique id has
been set by introducing a helper to do that for standard fuse_req
requests. FUSE_FORGET requests are not covered by this because they
appear to be synthesized into the event stream without a fuse_req
object and are never replied to.

Requests that are aborted without ever having been submitted to the fuse
server retain the behavior that only the fuse_request_end tracepoint
shows up in the trace record, and with req==0.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
fs/fuse/fuse_i.h | 5 +++++
fs/fuse/dev.c | 27 +++++++++++++++++++++++----
fs/fuse/dev_uring.c | 4 ++--
fs/fuse/virtio_fs.c | 3 +--
4 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 8edca9ad13a9d1..e93a3c3f11d901 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1254,6 +1254,11 @@ static inline ssize_t fuse_simple_idmap_request(struct mnt_idmap *idmap,
int fuse_simple_background(struct fuse_mount *fm, struct fuse_args *args,
gfp_t gfp_flags);

+/**
+ * Assign a unique id to a fuse request
+ */
+void fuse_request_assign_unique(struct fuse_iqueue *fiq, struct fuse_req *req);
+
/**
* End a finished request
*/
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index dcd338b65b2fc7..f06208e4364642 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -370,12 +370,32 @@ void fuse_dev_queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
}
}

+static inline void fuse_request_assign_unique_locked(struct fuse_iqueue *fiq,
+ struct fuse_req *req)
+{
+ if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
+ req->in.h.unique = fuse_get_unique_locked(fiq);
+
+ /* tracepoint captures in.h.unique and in.h.len */
+ trace_fuse_request_send(req);
+}
+
+inline void fuse_request_assign_unique(struct fuse_iqueue *fiq,
+ struct fuse_req *req)
+{
+ if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
+ req->in.h.unique = fuse_get_unique(fiq);
+
+ /* tracepoint captures in.h.unique and in.h.len */
+ trace_fuse_request_send(req);
+}
+EXPORT_SYMBOL_GPL(fuse_request_assign_unique);
+
static void fuse_dev_queue_req(struct fuse_iqueue *fiq, struct fuse_req *req)
{
spin_lock(&fiq->lock);
if (fiq->connected) {
- if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
- req->in.h.unique = fuse_get_unique_locked(fiq);
+ fuse_request_assign_unique_locked(fiq, req);
list_add_tail(&req->list, &fiq->pending);
fuse_dev_wake_and_unlock(fiq);
} else {
@@ -398,7 +418,6 @@ static void fuse_send_one(struct fuse_iqueue *fiq, struct fuse_req *req)
req->in.h.len = sizeof(struct fuse_in_header) +
fuse_len_args(req->args->in_numargs,
(struct fuse_arg *) req->args->in_args);
- trace_fuse_request_send(req);
fiq->ops->send_req(fiq, req);
}

@@ -688,10 +707,10 @@ static bool fuse_request_queue_background_uring(struct fuse_conn *fc,
{
struct fuse_iqueue *fiq = &fc->iq;

- req->in.h.unique = fuse_get_unique(fiq);
req->in.h.len = sizeof(struct fuse_in_header) +
fuse_len_args(req->args->in_numargs,
(struct fuse_arg *) req->args->in_args);
+ fuse_request_assign_unique(fiq, req);

return fuse_uring_queue_bq_req(req);
}
diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index 249b210becb1cc..7b541aeea1813f 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -7,6 +7,7 @@
#include "fuse_i.h"
#include "dev_uring_i.h"
#include "fuse_dev_i.h"
+#include "fuse_trace.h"

#include <linux/fs.h>
#include <linux/io_uring/cmd.h>
@@ -1268,8 +1269,7 @@ void fuse_uring_queue_fuse_req(struct fuse_iqueue *fiq, struct fuse_req *req)
if (!queue)
goto err;

- if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
- req->in.h.unique = fuse_get_unique(fiq);
+ fuse_request_assign_unique(fiq, req);

spin_lock(&queue->lock);
err = -ENOTCONN;
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 76c8fd0bfc75d5..a880294549a6bd 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -1480,8 +1480,7 @@ static void virtio_fs_send_req(struct fuse_iqueue *fiq, struct fuse_req *req)
struct virtio_fs_vq *fsvq;
int ret;

- if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
- req->in.h.unique = fuse_get_unique(fiq);
+ fuse_request_assign_unique(fiq, req);

clear_bit(FR_PENDING, &req->flags);