Re: [PATCH v2 5.15] io_uring: auto-removal for direct open/accept

[Pavel Begunkov <asml.silence@gmail.com>]

On 9/14/21 4:36 PM, Jens Axboe wrote:
> On 9/14/21 9:12 AM, Pavel Begunkov wrote:
>> It might be inconvenient that direct open/accept deviates from the
>> update semantics and fails if the slot is taken instead of removing a
>> file sitting there. Implement this auto-removal.
>>
>> Note that removal might need to allocate and so may fail. However, if an
>> empty slot is specified, it's guaraneed to not fail on the fd
>> installation side for valid userspace programs. It's needed for users
>> who can't tolerate such failures, e.g. accept where the other end
>> never retries.
>>
>> Suggested-by: Franz-B. Tuneke <franz-bernhard.tuneke@tu-dortmund.de>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>>
>> v2: simplify io_rsrc_node_switch_start() handling
>>
>>  fs/io_uring.c | 52 +++++++++++++++++++++++++++++++++------------------
>>  1 file changed, 34 insertions(+), 18 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index a864a94364c6..58c0cbfdd128 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -8287,11 +8287,27 @@ static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
>>  #endif
>>  }
>>  
>> +static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
>> +				 struct io_rsrc_node *node, void *rsrc)
>> +{
>> +	struct io_rsrc_put *prsrc;
>> +
>> +	prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
>> +	if (!prsrc)
>> +		return -ENOMEM;
>> +
>> +	prsrc->tag = *io_get_tag_slot(data, idx);
>> +	prsrc->rsrc = rsrc;
>> +	list_add(&prsrc->list, &node->rsrc_list);
>> +	return 0;
>> +}
> 
> I know this code is just being moved, but I tend to like making the
> expected/fast path inline:

I think it's more natural as now, as we always have

ret = do_something();
if (ret)
    return ret;
ret = do_something2();
if (ret)
    goto err;


And I remember you telling once "... I tend to like to do the error
path like that unless it's a hot path ...". So maybe just add
unlikely()?


> prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
> if (prsrc) {
> 	prsrc->tag = *io_get_tag_slot(data, idx);
> 	prsrc->rsrc = rsrc;
> 	list_add(&prsrc->list, &node->rsrc_list);
> 	return 0;
> }
> return -ENOMEM;
> 

-- 
Pavel Begunkov