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From: Al Viro <viro@zeniv.linux.org.uk>
To: Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	torvalds@linux-foundation.org
Subject: Re: [PATCH 1/3] iov_iter: add helper to save iov_iter state
Date: Fri, 10 Sep 2021 18:50:43 +0000	[thread overview]
Message-ID: <YTupAx9W2RcLJHGk@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <20210910182536.685100-2-axboe@kernel.dk>

On Fri, Sep 10, 2021 at 12:25:34PM -0600, Jens Axboe wrote:
> +void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state,
> +		      ssize_t did_bytes)
> +{
> +	if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) &&
> +			 !iov_iter_is_kvec(i))
> +		return;
> +	i->iov_offset = state->iov_offset;
> +	i->count = state->count;
> +	/*
> +	 * For the *vec iters, nr_segs + iov is constant - if we increment
> +	 * the vec, then we also decrement the nr_segs count. Hence we don't
> +	 * need to track both of these, just one is enough and we can deduct
> +	 * the other from that. ITER_{BVEC,IOVEC,KVEC} all have their pointers
> +	 * unionized, so we don't need to handle them individually.
> +	 */
> +	i->iov -= state->nr_segs - i->nr_segs;
> +	i->nr_segs = state->nr_segs;
> +}

No.  You can have iovec and kvec handled jointly (struct iovec and struct kvec
always have the same size).  You can *not* do that to bvec - check sizeof of
struct bio_vec and struct iovec on 32bit targets.

  reply	other threads:[~2021-09-10 18:50 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 18:25 [PATCHSET 0/3] Add ability to save/restore " Jens Axboe
2021-09-10 18:25 ` [PATCH 1/3] iov_iter: add helper to save " Jens Axboe
2021-09-10 18:50   ` Al Viro [this message]
2021-09-10 19:15     ` [PATCH v2 " Jens Axboe
2021-09-10 18:25 ` [PATCH 2/3] io_uring: use iov_iter state save/restore helpers Jens Axboe
2021-09-10 18:25 ` [PATCH 3/3] Revert "iov_iter: track truncated size" Jens Axboe
2021-09-13 22:43 ` [PATCHSET 0/3] Add ability to save/restore iov_iter state Jens Axboe
2021-09-13 23:23   ` Linus Torvalds
2021-09-14  1:54     ` Jens Axboe
2021-09-14 14:17 [PATCHSET v2 " Jens Axboe
2021-09-14 14:17 ` [PATCH 1/3] iov_iter: add helper to save " Jens Axboe
2021-09-15 16:29 [PATCHSET v3 0/3] Add ability to save/restore " Jens Axboe
2021-09-15 16:29 ` [PATCH 1/3] iov_iter: add helper to save " Jens Axboe

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