linux-kernel - Re: [RFC PATCH 03/11] vfs: Use init

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Date:   Fri, 30 Jun 2023 09:39:30 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>
Cc:     Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>,
        Christian Brauner <christian@...uner.io>
Subject: Re: [RFC PATCH 03/11] vfs: Use init_kiocb() to initialise new IOCBs

On 6/30/23 9:25?AM, David Howells wrote:
> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index 1bce2208b65c..1cade1567162 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -655,12 +655,13 @@ static bool need_complete_io(struct io_kiocb *req)
>  		S_ISBLK(file_inode(req->file)->i_mode);
>  }
>  
> -static int io_rw_init_file(struct io_kiocb *req, fmode_t mode)
> +static int io_rw_init_file(struct io_kiocb *req, unsigned int io_direction)
>  {
>  	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
>  	struct kiocb *kiocb = &rw->kiocb;
>  	struct io_ring_ctx *ctx = req->ctx;
>  	struct file *file = req->file;
> +	fmode_t mode = (io_direction == WRITE) ? FMODE_WRITE : FMODE_READ;
>  	int ret;
>  
>  	if (unlikely(!file || !(file->f_mode & mode)))

Not ideal to add a branch here, probably better to just pass in both?

> @@ -870,7 +871,7 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
>  		iov_iter_restore(&s->iter, &s->iter_state);
>  		iovec = NULL;
>  	}
> -	ret = io_rw_init_file(req, FMODE_WRITE);
> +	ret = io_rw_init_file(req, WRITE);
>  	if (unlikely(ret)) {
>  		kfree(iovec);
>  		return ret;
> @@ -914,7 +915,6 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
>  		__sb_writers_release(file_inode(req->file)->i_sb,
>  					SB_FREEZE_WRITE);
>  	}
> -	kiocb->ki_flags |= IOCB_WRITE;
>  
>  	if (likely(req->file->f_op->write_iter))
>  		ret2 = call_write_iter(req->file, kiocb, &s->iter);
> 

One concern here is that we're using IOCB_WRITE here to tell if
sb_start_write() has been done or not, and hence whether
kiocb_end_write() needs to be called. You know set it earlier, which
means if we get a failure if we need to setup async data, then we know
have IOCB_WRITE set at that point even though we did not call
sb_start_write().

-- 
Jens Axboe