Re: [PATCH v3 2/2] io_uring: add support for ftruncate

[Jens Axboe <axboe@kernel.dk>]

On 1/23/24 2:19 PM, Tony Solomonik wrote:
> Libraries that are built on io_uring currently need to maintain a
> separate thread pool implementation when they want to truncate a file.

Since we're getting down to nit picking, this commit message is not good
at all. It states a need, but it should also mention something ala:

This patch adds support for doing truncate through io_uring, eliminating
the need for applications to roll their own thread pool or offload
mechanism to be able to do non-blocking truncates.

> @@ -469,6 +470,11 @@ const struct io_issue_def io_issue_defs[] = {
>  		.prep			= io_eopnotsupp_prep,
>  #endif
>  	},
> +	[IORING_OP_FTRUNCATE] = {
> +		.needs_file		= 1,
> +		.prep			= io_ftruncate_prep,
> +		.issue			= io_ftruncate,
> +	},
>  };

Probably want to set hash_reg_file = 1 here as well, as it kind of works
like a buffered write in terms of serialization. Not strictly required,
as I can't see anything sane doing overlapping writes or truncates.

> diff --git a/io_uring/truncate.c b/io_uring/truncate.c
> new file mode 100644
> index 000000000000..4b48376149f9
> --- /dev/null
> +++ b/io_uring/truncate.c
> @@ -0,0 +1,48 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +#include <linux/fs.h>
> +#include <linux/file.h>
> +#include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/syscalls.h>
> +#include <linux/io_uring.h>
> +
> +#include <uapi/linux/io_uring.h>
> +
> +#include "../fs/internal.h"
> +
> +#include "io_uring.h"
> +#include "truncate.h"
> +
> +struct io_ftrunc {
> +	struct file			*file;
> +	loff_t				len;
> +};
> +
> +int io_ftruncate_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> +{
> +	struct io_ftrunc *ft = io_kiocb_to_cmd(req, struct io_ftrunc);
> +
> +	if (sqe->rw_flags || sqe->addr || sqe->len || sqe->buf_index ||
> +	    sqe->splice_fd_in || sqe->addr3)
> +		return -EINVAL;
> +
> +	ft->len = READ_ONCE(sqe->off);
> +
> +	req->flags |= REQ_F_FORCE_ASYNC;
> +	return 0;
> +}
> +
> +int io_ftruncate(struct io_kiocb *req, unsigned int issue_flags)
> +{
> +	struct io_ftrunc *ft = io_kiocb_to_cmd(req, struct io_ftrunc);
> +	int ret;
> +
> +	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
> +
> +	ret = ftruncate_file(req->file, ft->len, 0);
> +
> +	io_req_set_res(req, ret, 0);
> +	return IOU_OK;
> +}
> diff --git a/io_uring/truncate.h b/io_uring/truncate.h
> new file mode 100644
> index 000000000000..ec088293a478
> --- /dev/null
> +++ b/io_uring/truncate.h
> @@ -0,0 +1,4 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +int io_ftruncate_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
> +int io_ftruncate(struct io_kiocb *req, unsigned int issue_flags);

Rest looks good to me!

-- 
Jens Axboe