[PATCH 1/3] io_uring: add support for async work inheriting files table

[Jens Axboe <axboe@kernel.dk>]

This is in preparation for adding opcodes that need to modify files
in a process file table, either adding new ones or closing old ones.

If an opcode needs this, it must set REQ_F_NEED_FILES in the request
structure. If work that needs to get punted to async context have this
set, they will grab a reference to the process file table. When the
work is completed, the reference is dropped again.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 635856023fdf..ad462237275e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -267,10 +267,11 @@ struct io_ring_ctx {
 struct sqe_submit {
 	const struct io_uring_sqe	*sqe;
 	unsigned short			index;
+	bool				has_user : 1;
+	bool				in_async : 1;
+	bool				needs_fixed_file : 1;
 	u32				sequence;
-	bool				has_user;
-	bool				in_async;
-	bool				needs_fixed_file;
+	struct files_struct		*files;
 };
 
 /*
@@ -323,6 +324,7 @@ struct io_kiocb {
 #define REQ_F_FAIL_LINK		256	/* fail rest of links */
 #define REQ_F_SHADOW_DRAIN	512	/* link-drain shadow req */
 #define REQ_F_TIMEOUT		1024	/* timeout request */
+#define REQ_F_NEED_FILES	2048	/* needs to assume file table */
 	u64			user_data;
 	u32			result;
 	u32			sequence;
@@ -2191,6 +2193,7 @@ static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
 static void io_sq_wq_submit_work(struct work_struct *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+	struct files_struct *old_files = NULL;
 	struct io_ring_ctx *ctx = req->ctx;
 	struct mm_struct *cur_mm = NULL;
 	struct async_list *async_list;
@@ -2220,6 +2223,10 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 				set_fs(USER_DS);
 			}
 		}
+		if (s->files && !old_files) {
+			old_files = current->files;
+			current->files = s->files;
+		}
 
 		if (!ret) {
 			s->has_user = cur_mm != NULL;
@@ -2312,6 +2319,11 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+	if (old_files) {
+		struct files_struct *files = current->files;
+		current->files = old_files;
+		put_files_struct(files);
+	}
 }
 
 /*
@@ -2413,6 +2425,8 @@ static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 
 			s->sqe = sqe_copy;
 			memcpy(&req->submit, s, sizeof(*s));
+			if (req->flags & REQ_F_NEED_FILES)
+				req->submit.files = get_files_struct(current);
 			list = io_async_list_from_sqe(ctx, s->sqe);
 			if (!io_add_to_prev_work(list, req)) {
 				if (list)
@@ -2633,6 +2647,7 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 		s->index = head;
 		s->sqe = &ctx->sq_sqes[head];
 		s->sequence = ctx->cached_sq_head;
+		s->files = NULL;
 		ctx->cached_sq_head++;
 		return true;
 	}
-- 
2.17.1