io_uring/cmd: allow multishot polled commands

Some commands like timestamping in the next patch can make use of
multishot polling, i.e. REQ_F_APOLL_MULTISHOT. Add support for that,
which is condensed in a single helper called io_cmd_poll_multishot().

The user who wants to continue with a request in a multishot mode must
call the function, and only if it returns 0 the user is free to proceed.
Apart from normal terminal errors, it can also end up with -EIOCBQUEUED,
in which case the user must forward it to the core io_uring. It's
forbidden to use task work while the request is executing in a multishot
mode.

The API is not foolproof, hence it's not exported to modules nor exposed
in public headers.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/bcf97c31659662c72b69fc8fcdf2a88cfc16e430.1750065793.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 23 insertions, 0 deletions

diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 9ad0ea5398c2..02cec6231831 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -12,6 +12,7 @@
 #include "alloc_cache.h"
 #include "rsrc.h"
 #include "uring_cmd.h"
+#include "poll.h"
 
 void io_cmd_cache_free(const void *entry)
 {
@@ -136,6 +137,9 @@ void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
 {
 	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
 
+	if (WARN_ON_ONCE(req->flags & REQ_F_APOLL_MULTISHOT))
+		return;
+
 	ioucmd->task_work_cb = task_work_cb;
 	req->io_task_work.func = io_uring_cmd_work;
 	__io_req_task_work_add(req, flags);
@@ -158,6 +162,9 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, u64 res2,
 {
 	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
 
+	if (WARN_ON_ONCE(req->flags & REQ_F_APOLL_MULTISHOT))
+		return;
+
 	io_uring_cmd_del_cancelable(ioucmd, issue_flags);
 
 	if (ret < 0)
@@ -305,3 +312,19 @@ void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd)
 
 	io_req_queue_iowq(req);
 }
+
+int io_cmd_poll_multishot(struct io_uring_cmd *cmd,
+			  unsigned int issue_flags, __poll_t mask)
+{
+	struct io_kiocb *req = cmd_to_io_kiocb(cmd);
+	int ret;
+
+	if (likely(req->flags & REQ_F_APOLL_MULTISHOT))
+		return 0;
+
+	req->flags |= REQ_F_APOLL_MULTISHOT;
+	mask &= ~EPOLLONESHOT;
+
+	ret = io_arm_apoll(req, issue_flags, mask);
+	return ret == IO_APOLL_OK ? -EIOCBQUEUED : -ECANCELED;
+}