linux-ext4 - Re: [PATCH 1/8] nowait aio: Introduce IOCB_FLAG

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Date:   Wed, 1 Mar 2017 07:36:48 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     jack@...e.com, hch@...radead.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: 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 <rgoldwyn@...e.com>
> 
> 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.