From: Jens Axboe <axboe@kernel.dk>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org,
brauner@kernel.org
Subject: Re: [PATCH 2/8] iov_iter: add iovec_nr_user_vecs() helper
Date: Tue, 28 Mar 2023 13:27:32 -0600 [thread overview]
Message-ID: <8f36e443-e072-3c85-4ff9-b76476d7b98f@kernel.dk> (raw)
In-Reply-To: <20230328184220.GL3390869@ZenIV>
On 3/28/23 12:42 PM, Al Viro wrote:
> On Tue, Mar 28, 2023 at 11:36:07AM -0600, Jens Axboe wrote:
>> This returns the number of user segments in an iov_iter. The input can
>> either be an ITER_IOVEC, where it'll return the number of iovecs. Or it
>> can be an ITER_UBUF, in which case the number of segments is always 1.
>>
>> Outside of those two, no user backed iterators exist. Just return 0 for
>> those.
>
> Umm... Why not set ->nr_segs to 1 in iov_iter_ubuf() instead? Note that
> it won't be more costly; that part of struct iov_iter (8 bytes at offset 40
> on amd64) is *not* left uninitialized - zero gets stored there. That way
> you'll get constant 1 stored there, which is just as cheap...
Good point, let's have a prep patch that does that too.
--
Jens Axboe
next prev parent reply other threads:[~2023-03-28 19:27 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-28 17:36 [PATCHSET v4 0/8] Turn single segment imports into ITER_UBUF Jens Axboe
2023-03-28 17:36 ` [PATCH 1/8] iov_iter: teach iov_iter_iovec() to deal with ITER_UBUF Jens Axboe
2023-03-28 17:36 ` [PATCH 2/8] iov_iter: add iovec_nr_user_vecs() helper Jens Axboe
2023-03-28 18:42 ` Al Viro
2023-03-28 18:45 ` Linus Torvalds
2023-03-28 19:27 ` Jens Axboe [this message]
2023-03-28 17:36 ` [PATCH 3/8] snd: move mapping an iov_iter to user bufs into a helper Jens Axboe
2023-03-28 17:36 ` [PATCH 4/8] snd: make snd_map_bufs() deal with ITER_UBUF Jens Axboe
2023-03-28 17:50 ` Linus Torvalds
2023-03-28 17:52 ` Jens Axboe
2023-03-28 18:52 ` Al Viro
2023-03-28 19:28 ` Jens Axboe
2023-03-28 17:36 ` [PATCH 5/8] IB/hfi1: make hfi1_write_iter() deal with ITER_UBUF iov_iter Jens Axboe
2023-03-28 18:43 ` Linus Torvalds
2023-03-28 18:55 ` Matthew Wilcox
2023-03-28 19:05 ` Linus Torvalds
2023-03-28 19:16 ` Linus Torvalds
2023-03-28 21:21 ` Jens Axboe
2023-03-28 21:38 ` Jens Axboe
2023-03-28 21:51 ` Jens Axboe
2023-03-28 19:30 ` Jens Axboe
2023-03-28 20:38 ` Al Viro
2023-03-28 20:46 ` Jens Axboe
2023-03-28 22:06 ` Linus Torvalds
2023-03-28 17:36 ` [PATCH 6/8] IB/qib: make qib_write_iter() " Jens Axboe
2023-03-28 17:36 ` [PATCH 7/8] iov_iter: convert import_single_range() to ITER_UBUF Jens Axboe
2023-03-28 17:36 ` [PATCH 8/8] iov_iter: import single vector iovecs as ITER_UBUF Jens Axboe
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