[PATCH 5.15] io_uring: auto-removal for direct open/accept

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

It might be inconvenient that direct open/accept deviates from the
update semantics and fails if the slot is taken instead of removing a
file sitting there. Implement the auto-removal.

Note that removal might need to allocate and so may fail. However, if an
empty slot is specified, it's guaraneed to not fail on the fd
installation side. It's needed for users that can't tolerate spuriously
closed files, e.g. accepts where the other end doesn't expect it.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 fs/io_uring.c | 59 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 18 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a864a94364c6..29bca3a1ddeb 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7672,6 +7672,7 @@ static void io_rsrc_node_switch(struct io_ring_ctx *ctx,
 	}
 }
 
+/* before changing see io_install_fixed_file(), it might ignore errors */
 static int io_rsrc_node_switch_start(struct io_ring_ctx *ctx)
 {
 	if (ctx->rsrc_backup_node)
@@ -8287,11 +8288,27 @@ static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
 #endif
 }
 
+static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
+				 struct io_rsrc_node *node, void *rsrc)
+{
+	struct io_rsrc_put *prsrc;
+
+	prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
+	if (!prsrc)
+		return -ENOMEM;
+
+	prsrc->tag = *io_get_tag_slot(data, idx);
+	prsrc->rsrc = rsrc;
+	list_add(&prsrc->list, &node->rsrc_list);
+	return 0;
+}
+
 static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 				 unsigned int issue_flags, u32 slot_index)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
+	bool needs_switch = false;
 	struct io_fixed_file *file_slot;
 	int ret = -EBADF;
 
@@ -8304,12 +8321,31 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 	ret = -EINVAL;
 	if (slot_index >= ctx->nr_user_files)
 		goto err;
+	/*
+	 * Ignore error, ->rsrc_backup_node is not needed if the slot is empty,
+	 * and we'd rather not drop the file.
+	 */
+	io_rsrc_node_switch_start(ctx);
 
 	slot_index = array_index_nospec(slot_index, ctx->nr_user_files);
 	file_slot = io_fixed_file_slot(&ctx->file_table, slot_index);
-	ret = -EBADF;
-	if (file_slot->file_ptr)
-		goto err;
+
+	if (file_slot->file_ptr) {
+		struct file *old_file;
+
+		if (!ctx->rsrc_backup_node) {
+			ret = -ENOMEM;
+			goto err;
+		}
+
+		old_file = (struct file *)(file_slot->file_ptr & FFS_MASK);
+		ret = io_queue_rsrc_removal(ctx->file_data, slot_index,
+					    ctx->rsrc_node, old_file);
+		if (ret)
+			goto err;
+		file_slot->file_ptr = 0;
+		needs_switch = true;
+	}
 
 	*io_get_tag_slot(ctx->file_data, slot_index) = 0;
 	io_fixed_file_set(file_slot, file);
@@ -8321,27 +8357,14 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 
 	ret = 0;
 err:
+	if (needs_switch)
+		io_rsrc_node_switch(ctx, ctx->file_data);
 	io_ring_submit_unlock(ctx, !force_nonblock);
 	if (ret)
 		fput(file);
 	return ret;
 }
 
-static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
-				 struct io_rsrc_node *node, void *rsrc)
-{
-	struct io_rsrc_put *prsrc;
-
-	prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
-	if (!prsrc)
-		return -ENOMEM;
-
-	prsrc->tag = *io_get_tag_slot(data, idx);
-	prsrc->rsrc = rsrc;
-	list_add(&prsrc->list, &node->rsrc_list);
-	return 0;
-}
-
 static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 				 struct io_uring_rsrc_update2 *up,
 				 unsigned nr_args)
-- 
2.33.0