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Message-ID: <566c700c-d3d5-4899-8de1-87092e76310c@gmail.com>
Date: Tue, 18 Mar 2025 07:25:51 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Sidong Yang <sidong.yang@...iosa.ai>, Jens Axboe <axboe@...nel.dk>
Cc: Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
io-uring@...r.kernel.org
Subject: Re: [RFC PATCH v4 4/5] btrfs: ioctl: introduce
btrfs_uring_import_iovec()
On 3/18/25 01:58, Sidong Yang wrote:
> On Mon, Mar 17, 2025 at 09:40:05AM -0600, Jens Axboe wrote:
>> On 3/17/25 7:57 AM, Sidong Yang wrote:
>>> This patch introduces btrfs_uring_import_iovec(). In encoded read/write
>>> with uring cmd, it uses import_iovec without supporting fixed buffer.
>>> btrfs_using_import_iovec() could use fixed buffer if cmd flags has
>>> IORING_URING_CMD_FIXED.
>>>
>>> Signed-off-by: Sidong Yang <sidong.yang@...iosa.ai>
>>> ---
>>> fs/btrfs/ioctl.c | 32 ++++++++++++++++++++++++--------
>>> 1 file changed, 24 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>>> index 6c18bad53cd3..a7b52fd99059 100644
>>> --- a/fs/btrfs/ioctl.c
>>> +++ b/fs/btrfs/ioctl.c
>>> @@ -4802,6 +4802,28 @@ struct btrfs_uring_encoded_data {
>>> struct iov_iter iter;
>>> };
>>>
>>> +static int btrfs_uring_import_iovec(struct io_uring_cmd *cmd,
>>> + unsigned int issue_flags, int rw)
>>> +{
>>> + struct btrfs_uring_encoded_data *data =
>>> + io_uring_cmd_get_async_data(cmd)->op_data;
>>> + int ret;
>>> +
>>> + if (cmd && (cmd->flags & IORING_URING_CMD_FIXED)) {
>>> + data->iov = NULL;
>>> + ret = io_uring_cmd_import_fixed_vec(cmd, data->args.iov,
>>> + data->args.iovcnt,
>>> + ITER_DEST, issue_flags,
>>> + &data->iter);
>>> + } else {
>>> + data->iov = data->iovstack;
>>> + ret = import_iovec(rw, data->args.iov, data->args.iovcnt,
>>> + ARRAY_SIZE(data->iovstack), &data->iov,
>>> + &data->iter);
>>> + }
>>> + return ret;
>>> +}
>>
>> How can 'cmd' be NULL here?
>
> It seems that there is no checkes for 'cmd' before and it works same as before.
> But I think it's better to add a check in function start for safety.
The check goes two lines after you already dereferenced it, and it
seems to be called from io_uring cmd specific code. The null check
only adds to confusion.
--
Pavel Begunkov
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