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From: Nadav Amit <[email protected]>
To: Jens Axboe <[email protected]>
Cc: "[email protected]" <[email protected]>,
	Andrea Arcangeli <[email protected]>,
	Peter Xu <[email protected]>,
	Alexander Viro <[email protected]>,
	"[email protected]" <[email protected]>,
	LKML <[email protected]>,
	"[email protected]" <[email protected]>
Subject: Re: [RFC PATCH 07/13] fs/userfaultfd: support read_iter to use io_uring
Date: Mon, 30 Nov 2020 19:23:07 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

> On Nov 30, 2020, at 10:20 AM, Jens Axboe <[email protected]> wrote:
> 
> On 11/28/20 5:45 PM, Nadav Amit wrote:
>> From: Nadav Amit <[email protected]>
>> 
>> iouring with userfaultfd cannot currently be used fixed buffers since
>> userfaultfd does not provide read_iter(). This is required to allow
>> asynchronous (queued) reads from userfaultfd.
>> 
>> To support async-reads of userfaultfd provide read_iter() instead of
>> read().
>> 
>> Cc: Jens Axboe <[email protected]>
>> Cc: Andrea Arcangeli <[email protected]>
>> Cc: Peter Xu <[email protected]>
>> Cc: Alexander Viro <[email protected]>
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
>> Signed-off-by: Nadav Amit <[email protected]>
>> ---
>> fs/userfaultfd.c | 18 ++++++++++--------
>> 1 file changed, 10 insertions(+), 8 deletions(-)
>> 
>> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
>> index b6a04e526025..6333b4632742 100644
>> --- a/fs/userfaultfd.c
>> +++ b/fs/userfaultfd.c
>> @@ -1195,9 +1195,9 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
>> 	return ret;
>> }
>> 
>> -static ssize_t userfaultfd_read(struct file *file, char __user *buf,
>> -				size_t count, loff_t *ppos)
>> +static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
>> {
>> +	struct file *file = iocb->ki_filp;
>> 	struct userfaultfd_ctx *ctx = file->private_data;
>> 	ssize_t _ret, ret = 0;
>> 	struct uffd_msg msg;
>> @@ -1207,16 +1207,18 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
>> 		return -EINVAL;
>> 
>> 	for (;;) {
>> -		if (count < sizeof(msg))
>> +		if (iov_iter_count(to) < sizeof(msg))
>> 			return ret ? ret : -EINVAL;
>> 		_ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
> 
> 'no_wait' should be changed to factor in iocb->ki_flags & IOCB_NOWAIT as well,
> not just f_flags & O_NONBLOCK.
> 
> I didn't check your write_iter, but if appropriate, that should do that
> too.

Thanks, I completely missed this point and will fix it in v1 (if I get
a positive feedback on the rest from the userfaultfd people).


  reply	other threads:[~2020-11-30 19:24 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-29  0:45 [RFC PATCH 00/13] fs/userfaultfd: support iouring and polling Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 01/13] fs/userfaultfd: fix wrong error code on WP & !VM_MAYWRITE Nadav Amit
2020-12-01 21:22   ` Mike Kravetz
2020-12-21 19:01     ` Peter Xu
2020-11-29  0:45 ` [RFC PATCH 02/13] fs/userfaultfd: fix wrong file usage with iouring Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 03/13] selftests/vm/userfaultfd: wake after copy failure Nadav Amit
2020-12-21 19:28   ` Peter Xu
2020-12-21 19:51     ` Nadav Amit
2020-12-21 20:52       ` Peter Xu
2020-12-21 20:54         ` Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 04/13] fs/userfaultfd: simplify locks in userfaultfd_ctx_read Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 05/13] fs/userfaultfd: introduce UFFD_FEATURE_POLL Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 06/13] iov_iter: support atomic copy_page_from_iter_iovec() Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 07/13] fs/userfaultfd: support read_iter to use io_uring Nadav Amit
2020-11-30 18:20   ` Jens Axboe
2020-11-30 19:23     ` Nadav Amit [this message]
2020-11-29  0:45 ` [RFC PATCH 08/13] fs/userfaultfd: complete reads asynchronously Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 09/13] fs/userfaultfd: use iov_iter for copy/zero Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 10/13] fs/userfaultfd: add write_iter() interface Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 11/13] fs/userfaultfd: complete write asynchronously Nadav Amit
2020-12-02  7:12   ` Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 12/13] fs/userfaultfd: kmem-cache for wait-queue objects Nadav Amit
2020-11-30 19:51   ` Nadav Amit
2020-11-29  0:45 ` [RFC PATCH 13/13] selftests/vm/userfaultfd: iouring and polling tests Nadav Amit

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