Re: [PATCH] nbd: fix partial sending

[Jens Axboe <axboe@kernel.dk>]

On 10/17/24 9:13 AM, Bart Van Assche wrote:
> On 10/17/24 4:36 AM, Ming Lei wrote:
>> +static blk_status_t nbd_send_pending_cmd(struct nbd_device *nbd,
>> +        struct nbd_cmd *cmd)
>> +{
>> +    struct request *req = blk_mq_rq_from_pdu(cmd);
>> +    unsigned long deadline = READ_ONCE(req->deadline);
>> +    unsigned int wait_ms = 2;
>> +    blk_status_t res;
>> +
>> +    WARN_ON_ONCE(test_bit(NBD_CMD_REQUEUED, &cmd->flags));
>> +
>> +    while (true) {
>> +        res = nbd_send_cmd(nbd, cmd, cmd->index);
>> +        if (res != BLK_STS_RESOURCE)
>> +            return res;
>> +        if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline)
>> +            break;
>> +        msleep(wait_ms);
>> +        wait_ms *= 2;
>> +    }
> 
> I think that there are better solutions to wait until more data
> can be sent, e.g. by using the kernel equivalent of the C library
> function select().

It's vfs_poll() - but I don't think that'd be worth it here, the nbd
driver sets BLK_MQ_F_BLOCKING anyway. Using a poll trigger for this
would be a lot more complicated, and need quite a bit of support code.

-- 
Jens Axboe