Re: [PATCH 1/8] nowait aio: Introduce IOCB_FLAG_NOWAIT

On Tue, Feb 28, 2017 at 05:36:03PM -0600, Goldwyn Rodrigues wrote:

From: Goldwyn Rodrigues <redacted>

This flag informs kernel to bail out if an AIO request will block
for reasons such as file allocations, or a writeback triggered,
or would block while allocating requests while performing
direct I/O.

IOCB_FLAG_NOWAIT is translated to IOCB_NOWAIT for
iocb->ki_flags.

Given that we aren't validating aio_flags in older kernels we can't
just add this flag as it will be a no-op in older kernels.  I think
we will have to add IOCB_CMD_PREADV2/IOCB_CMD_WRITEV2 opcodes that
properly validate all reserved fields or flags first.

Once we do that I'd really prefer to use the same flags values
as preadv2/pwritev2 so that we'll only need one set of flags over
sync/async read/write ops.