Re: [PATCH 3/6] io_uring: allow allocated fixed files for openat/openat2

[Jens Axboe <axboe@kernel.dk>]

On 5/13/22 6:25 AM, Jens Axboe wrote:
> On 5/12/22 11:28 PM, Hao Xu wrote:
>> ? 2022/5/12 ??8:23, Jens Axboe ??:
>>> On 5/12/22 2:21 AM, Hao Xu wrote:
>>>> ? 2022/5/9 ??11:50, Jens Axboe ??:
>>>>> If the application passes in IORING_FILE_INDEX_ALLOC as the file_slot,
>>>>> then that's a hint to allocate a fixed file descriptor rather than have
>>>>> one be passed in directly.
>>>>>
>>>>> This can be useful for having io_uring manage the direct descriptor space.
>>>>>
>>>>> Normal open direct requests will complete with 0 for success, and < 0
>>>>> in case of error. If io_uring is asked to allocated the direct descriptor,
>>>>> then the direct descriptor is returned in case of success.
>>>>>
>>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>>> ---
>>>>>    fs/io_uring.c                 | 32 +++++++++++++++++++++++++++++---
>>>>>    include/uapi/linux/io_uring.h |  9 +++++++++
>>>>>    2 files changed, 38 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>>> index 8c40411a7e78..ef999d0e09de 100644
>>>>> --- a/fs/io_uring.c
>>>>> +++ b/fs/io_uring.c
>>>>> @@ -4697,7 +4697,7 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>>>>        return __io_openat_prep(req, sqe);
>>>>>    }
>>>>>    -static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
>>>>> +static int io_file_bitmap_get(struct io_ring_ctx *ctx)
>>>>>    {
>>>>>        struct io_file_table *table = &ctx->file_table;
>>>>>        unsigned long nr = ctx->nr_user_files;
>>>>> @@ -4722,6 +4722,32 @@ static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
>>>>>        return -ENFILE;
>>>>>    }
>>>>>    +static int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
>>>>> +                   struct file *file, unsigned int file_slot)
>>>>> +{
>>>>> +    int alloc_slot = file_slot == IORING_FILE_INDEX_ALLOC;
>>>>> +    struct io_ring_ctx *ctx = req->ctx;
>>>>> +    int ret;
>>>>> +
>>>>> +    if (alloc_slot) {
>>>>> +        io_ring_submit_lock(ctx, issue_flags);
>>>>> +        file_slot = io_file_bitmap_get(ctx);
>>>>> +        if (unlikely(file_slot < 0)) {
>>>>> +            io_ring_submit_unlock(ctx, issue_flags);
>>>>> +            return file_slot;
>>>>> +        }
>>>>> +    }
>>>>
>>>> if (alloc_slot) {
>>>>   ...
>>>> } else {
>>>>          file_slot -= 1;
>>>> }
>>>>
>>>> Otherwise there is off-by-one error.
>>>>
>>>> Others looks good,
>>>>
>>>> Reviewed-by: Hao Xu <howeyxu@tencent.com>
>>>
>>> Thanks, you are correct, I've folded that in.
>>>
>>
>> Hi Jens,
>> I've rebased multishot accept based on your fixed-alloc branch:
>>
>> https://github.com/HowHsu/linux/commits/for-5.19/io_uring_multishot_accept_v6
>>
>> Let me know when ixed-alloc is ready, then I'll do the final rebase
>> for multishot accept and send it to the list, including the liburing
>> change.
> 
> Just base it against for-5.19/io_uring, I'm fixing the one-off and
> pushing it out.

You can send it against now, I don't think there's any further changes
needed.

-- 
Jens Axboe