How to make a BufferedBidirectionalStreamBuf that uses custom buffering strategies?

[ethindp]

Hi all,

I'm hoping to write a custom BufferedBidirectionalStreamBuf that uses a custom buffering strategy. I'm hoping to wrap llfio (specifically llfio::file_handle), but the problem is that it uses functions like readv(2)/preadv(2)/preadv2(2)) (or Windows's equivalents) which means scatter/gather IO. Which can be incredible performance-wise, but it needs a bit of work to actually wrap into an iostream. I thought I could just do this but then I looked at the code for BufferedBidirectionalStreamBuf and apparently it allocates its own internal buffer. I... Guess this makes my job easier.... Should I just use that allocated buffer or should I override the constructor to do my own thing? My buffering strategy involves a buffer list for reading and writing, with each buffer being the page size of the system in question. When the buffer is filled, it flushes it all to disk. So essentially I'd be taking over the normal role of the FS cache (in a way) and bypassing it altogether.