[PATCH v3] io-wq: provide IO_WQ_* constants for IORING_REGISTER_IOWQ_MAX_WORKERS arg items

[Eugene Syromiatnikov <esyr@redhat.com>]

The items passed in the array pointed by the arg parameter
of IORING_REGISTER_IOWQ_MAX_WORKERS io_uring_register operation
carry certain semantics: they refer to different io-wq worker categories;
provide IO_WQ_* constants in the UAPI, so these categories can be referenced
in the user space code.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Complements: 2e480058ddc21ec5 ("io-wq: provide a way to limit max number of workers")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
v3:
 - Constants are named in accordance with the suggestion, the internal enum
   is no longer touched, BUILD_BUG_ON checks are added.

v2: https://lore.kernel.org/lkml/20210913104101.GA29616@asgard.redhat.com/
 - IO_WQ_ACCT_NR is no longer exposed directly in UAPI, per Jens Axboe's
    suggestion.

v1: https://lore.kernel.org/lkml/20210912122411.GA27679@asgard.redhat.com/
---
 fs/io-wq.c                    | 5 +++++
 include/uapi/linux/io_uring.h | 8 +++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 6c55362..3d21568 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -14,6 +14,7 @@
 #include <linux/rculist_nulls.h>
 #include <linux/cpu.h>
 #include <linux/tracehook.h>
+#include <uapi/linux/io_uring.h>
 
 #include "io-wq.h"
 
@@ -1287,6 +1288,10 @@ int io_wq_max_workers(struct io_wq *wq, int *new_count)
 {
 	int i, node, prev = 0;
 
+	BUILD_BUG_ON((int) IO_WQ_ACCT_BOUND   != (int) IO_WQ_BOUND);
+	BUILD_BUG_ON((int) IO_WQ_ACCT_UNBOUND != (int) IO_WQ_UNBOUND);
+	BUILD_BUG_ON((int) IO_WQ_ACCT_NR      != 2);
+
 	for (i = 0; i < 2; i++) {
 		if (new_count[i] > task_rlimit(current, RLIMIT_NPROC))
 			new_count[i] = task_rlimit(current, RLIMIT_NPROC);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 59ef351..b270a07 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -317,13 +317,19 @@ enum {
 	IORING_REGISTER_IOWQ_AFF		= 17,
 	IORING_UNREGISTER_IOWQ_AFF		= 18,
 
-	/* set/get max number of workers */
+	/* set/get max number of io-wq workers */
 	IORING_REGISTER_IOWQ_MAX_WORKERS	= 19,
 
 	/* this goes last */
 	IORING_REGISTER_LAST
 };
 
+/* io-wq worker categories */
+enum {
+	IO_WQ_BOUND,
+	IO_WQ_UNBOUND,
+};
+
 /* deprecated, see struct io_uring_rsrc_update */
 struct io_uring_files_update {
 	__u32 offset;
-- 
2.1.4