41ba7e9b13
The TTY buffers used the standard <sys/queue.h> lists. Unfortunately they have a big shortcoming. If you want to have a double linked list, but no tail pointer, it's still not possible to obtain the previous element in the list. Inside the buffers we don't need them. This is why I switched to custom linked list macros. The macros will also keep track of the amount of items in the list. Because it doesn't use a sentinel, we can just initialize the queues with zero. In its simplest form (the output queue), we will only keep two references to blocks in the queue, namely the head of the list and the last block in use. All free blocks are stored behind the last block in use. I noticed there was a very subtle bug in the previous code: in a very uncommon corner case, it would uma_zfree() a block in the queue before calling memcpy() to extract the data from the block.
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