Re: [PATCH] fs: io_uring.c: Add skip option for __io_sqe_files_update

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Sun, Dec 20, 2020 at 03:18:05PM +0000, Pavel Begunkov wrote:
> On 20/12/2020 06:50, noah wrote:> From: noah <goldstein.n@wustl.edu>
> > 
> > This patch makes it so that specify a file descriptor value of -2 will
> > skip updating the corresponding fixed file index.
> > 
> > This will allow for users to reduce the number of syscalls necessary
> > to update a sparse file range when using the fixed file option.
> 
> Answering the github thread -- it's indeed a simple change, I had it the
> same day you posted the issue. See below it's a bit cleaner. However, I
> want to first review "io_uring: buffer registration enhancements", and
> if it's good, for easier merging/etc I'd rather prefer to let it go
> first (even if partially).
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 941fe9b64fd9..b3ae9d5da17e 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7847,9 +7847,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>  	if (IS_ERR(ref_node))
>  		return PTR_ERR(ref_node);
>  
> -	done = 0;
>  	fds = u64_to_user_ptr(up->fds);
> -	while (nr_args) {
> +	for (done = 0; done < nr_args; done++) {
>  		struct fixed_file_table *table;
>  		unsigned index;
>  
> @@ -7858,7 +7857,10 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>  			err = -EFAULT;
>  			break;
>  		}
> -		i = array_index_nospec(up->offset, ctx->nr_user_files);
> +		if (fd == IORING_REGISTER_FILES_SKIP)
> +			continue;
> +
> +		i = array_index_nospec(up->offset + done, ctx->nr_user_files);
>  		table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
>  		index = i & IORING_FILE_TABLE_MASK;
>  		if (table->files[index]) {
> @@ -7896,9 +7898,6 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>  				break;
>  			}
>  		}
> -		nr_args--;
> -		done++;
> -		up->offset++;
>  	}
>  
>  	if (needs_switch) {
> 
> -- 
> Pavel Begunkov
Ah. Got it.