selftests/fuse: add FUSE io-uring integration test

jira SECO-478
RFE: FUSE_IO_URING
Add a kselftest for the FUSE io-uring request dispatch path.  A
minimal in-memory FUSE daemon runs in a thread, negotiates
FUSE_OVER_IO_URING during FUSE_INIT, and handles requests through
FUSE_IO_URING_CMD_REGISTER / FUSE_IO_URING_CMD_COMMIT_AND_FETCH.
An atomic counter verifies requests are served through io_uring.

Test cases:
  - read_file: read and verify file content
  - write_and_readback: write data, read it back, compare
  - readdir: list directory, verify entries
  - stat_files: stat root and file, verify attributes
  - concurrent_io: 4 threads doing interleaved reads and writes
  - requests_via_uring: per-operation verification that read, write,
    readdir, and stat each produce io_uring requests
  - sustained_io: write 256KB in 4KB chunks, read back, verify pattern
  - crash_recovery: fork daemon, SIGKILL with active I/O, verify
    kernel health
  - abort_before_ring_ready: negotiate io_uring but never register
    entries, abort connection, verify no deadlock or leak

Tests SKIP when prerequisites are not met (no root, io_uring
disabled, enable_uring != Y).

Signed-off-by: Brett Mastbergen <bmastbergen@ciq.com>

Author: bmastbergen

tools/testing/selftests/filesystems/fuse/.gitignore

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 fuse_mnt
+fuse_uring_test
 fusectl_test

tools/testing/selftests/filesystems/fuse/Makefile

@@ -5,6 +5,15 @@ CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
 TEST_GEN_PROGS := fusectl_test
 TEST_GEN_FILES := fuse_mnt
 
+# fuse_uring_test requires liburing; add it only when the library is present.
+URING_CFLAGS := $(shell pkg-config liburing --cflags 2>/dev/null)
+URING_LDLIBS := $(shell pkg-config liburing --libs 2>/dev/null)
+ifeq ($(URING_LDLIBS),)
+$(warning liburing not found; fuse_uring_test will be skipped)
+else
+TEST_GEN_PROGS += fuse_uring_test
+endif
+
 # fuse_acl_cache_test requires libfuse3; add it only when the library is present.
 ACL_CFLAGS := $(shell pkg-config fuse3 --cflags 2>/dev/null)
 ACL_LDLIBS := $(shell pkg-config fuse3 --libs 2>/dev/null)
@@ -36,3 +45,6 @@ $(OUTPUT)/fuse_mnt: LDLIBS += $(VAR_LDLIBS)
 
 $(OUTPUT)/fuse_acl_cache_test: CFLAGS += $(ACL_CFLAGS)
 $(OUTPUT)/fuse_acl_cache_test: LDLIBS += $(ACL_LDLIBS)
+
+$(OUTPUT)/fuse_uring_test: CFLAGS += $(URING_CFLAGS) -Wextra -Wno-unused-parameter -pthread
+$(OUTPUT)/fuse_uring_test: LDLIBS += $(URING_LDLIBS) -lpthread

tools/testing/selftests/filesystems/fuse/config

@@ -0,0 +1,3 @@
+CONFIG_FUSE_FS=m
+CONFIG_FUSE_IO_URING=y
+CONFIG_IO_URING=y