Yes, for reasons we haven't discovered, the block list can become quite long and read_avail walks the entire list every time. In contrast, read_avail_more_than(0) will just look at the first block.

I agree with that calling read_avail() should be avoided as much as possible. We observed that read_avail() made spin with long IOBufferBlock in other area in the past.

Looks this changes is doing logically same things without read_avail(). I bit worried about replacing memcpy() & consume() to read(), but it looks OK so far.

Actually, @masaori335, I think that's a bug. I want to talk with Susan before we commit this. I don't think read does the same thing as consume in this context.

Spoke with Susan, I misunderstood the IOBufferReader API. The code looks correct.

Cherry picked to 8.1.0