io_uring: let to set a range for file slot allocation

From recently io_uring provides an option to allocate a file index for
operation registering fixed files. However, it's utterly unusable with
mixed approaches when for a part of files the userspace knows better
where to place it, as it may race and users don't have any sane way to
pick a slot and hoping it will not be taken.

Let the userspace to register a range of fixed file slots in which the
auto-allocation happens. The use case is splittting the fixed table in
two parts, where on of them is used for auto-allocation and another for
slot-specified operations.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/66ab0394e436f38437cf7c44676e1920d09687ad.1656154403.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 20 insertions, 4 deletions

diff --git a/io_uring/filetable.c b/io_uring/filetable.c
index abaa5ba7f655..7b473259f3f4 100644
--- a/io_uring/filetable.c
+++ b/io_uring/filetable.c
@@ -16,7 +16,7 @@
 static int io_file_bitmap_get(struct io_ring_ctx *ctx)
 {
 	struct io_file_table *table = &ctx->file_table;
-	unsigned long nr = ctx->nr_user_files;
+	unsigned long nr = ctx->file_alloc_end;
 	int ret;
 
 	do {
@@ -24,11 +24,10 @@ static int io_file_bitmap_get(struct io_ring_ctx *ctx)
 		if (ret != nr)
 			return ret;
 
-		if (!table->alloc_hint)
+		if (table->alloc_hint == ctx->file_alloc_start)
 			break;
-
 		nr = table->alloc_hint;
-		table->alloc_hint = 0;
+		table->alloc_hint = ctx->file_alloc_start;
 	} while (1);
 
 	return -ENFILE;
@@ -175,3 +174,20 @@ int io_fixed_fd_remove(struct io_ring_ctx *ctx, unsigned int offset)
 	io_rsrc_node_switch(ctx, ctx->file_data);
 	return 0;
 }
+
+int io_register_file_alloc_range(struct io_ring_ctx *ctx,
+				 struct io_uring_file_index_range __user *arg)
+{
+	struct io_uring_file_index_range range;
+	u32 end;
+
+	if (copy_from_user(&range, arg, sizeof(range)))
+		return -EFAULT;
+	if (check_add_overflow(range.off, range.len, &end))
+		return -EOVERFLOW;
+	if (range.resv || end > ctx->nr_user_files)
+		return -EINVAL;
+
+	io_file_table_set_alloc_range(ctx, range.off, range.len);
+	return 0;
+}