io_uring: add basic fixed file allocator

Applications currently always pick where they want fixed files to go.
In preparation for allowing these types of commands with multishot
support, add a basic allocator in the fixed file table.

Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f8a685cc036354e7fc82fbb56a39821ae526d242..8c40411a7e78ceb19e4cc09bdb9f0e77e4e475c3 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -258,6 +258,7 @@ struct io_rsrc_put {
 struct io_file_table {
        struct io_fixed_file *files;
        unsigned long *bitmap;
+       unsigned int alloc_hint;
 };
 
 struct io_rsrc_node {
@@ -4696,6 +4697,31 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
        return __io_openat_prep(req, sqe);
 }
 
+static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
+{
+       struct io_file_table *table = &ctx->file_table;
+       unsigned long nr = ctx->nr_user_files;
+       int ret;
+
+       if (table->alloc_hint >= nr)
+               table->alloc_hint = 0;
+
+       do {
+               ret = find_next_zero_bit(table->bitmap, nr, table->alloc_hint);
+               if (ret != nr) {
+                       table->alloc_hint = ret + 1;
+                       return ret;
+               }
+               if (!table->alloc_hint)
+                       break;
+
+               nr = table->alloc_hint;
+               table->alloc_hint = 0;
+       } while (1);
+
+       return -ENFILE;
+}
+
 static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
 {
        struct open_flags op;
@@ -8664,11 +8690,14 @@ static inline void io_file_bitmap_set(struct io_file_table *table, int bit)
 {
        WARN_ON_ONCE(test_bit(bit, table->bitmap));
        __set_bit(bit, table->bitmap);
+       if (bit == table->alloc_hint)
+               table->alloc_hint++;
 }
 
 static inline void io_file_bitmap_clear(struct io_file_table *table, int bit)
 {
        __clear_bit(bit, table->bitmap);
+       table->alloc_hint = bit;
 }
 
 static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)