fs: expose scatter/gather syscalls writev() and readv()

[reqshark]

with the awesome work achieved here by @ronkorving in libuv/libuv@2bf7827

the upcoming libuv release will unblock #2167

first mentioned by @trevnorris in that PR, i think it makes a lot of sense to expose scatter/gather syscalls writev and also readv from node.js

[Trott]

@reqshark Can you elaborate a little on this? Or maybe link to the specific comment in the PR that you're referring to? Apologies in advance for my ignorance.

[reqshark]

@Trott oh ok, I remember now what this was about.

i was just thinking how cool would it be to do fs.writev and fs.readv?

API would operate by using fs.open first to get an fd and use it like we do on fs.read/fs.write

this would open the door to more efficient I/O for a wide variety of buffer sizes

[Trott]

#2167 landed. Anyone thinking this feature is a good idea and willing to try to implement and submit a pull request?

[refack]

Put into https://github.com/nodejs/node/projects/13 backlog

[zbjornson]

@refack did you intentionally change the title from "scatter/gather" to "setter/getter"? writev/readv are correctly called "scatter/gather" syscalls.

[reqshark]

nice catch @zbjornson!

[addaleax]

Fwiw, writev is already available on the internal fs binding (as writeBuffers), so that should be very easy to implement. readv shouldn’t be much harder.

I’d like to reopen this. It’s not a trivial first contribution, but if you know some C++ and can copy-paste the rest together, this should be doable (and I’m happy to help), so I’m adding good first contribution.