linux-kernel - Re: [RFC PATCH] io_uring: add support for IORING_OP

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Message-ID: <20210123235620.ue4n3p5wbuafs35b@alap3.anarazel.de>
Date:   Sat, 23 Jan 2021 15:56:20 -0800
From:   Andres Freund <andres@...razel.de>
To:     Lennert Buytenhek <buytenh@...tstofly.org>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        io-uring@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-btrfs@...r.kernel.org
Subject: Re: [RFC PATCH] io_uring: add support for IORING_OP_GETDENTS64

Hi,

On 2021-01-23 15:50:55 -0800, Andres Freund wrote:
> It's also not clear to me that right now you'd necessarily get correct
> results if multiple IORING_OP_GETDENTS64 for the same fd get processed
> in different workers.  Looking at iterate_dir(), it looks to me that the
> locking around the file position would end up being insufficient on
> filesystems that implement iterate_shared?
> [...]
> As there's only a shared lock, seems like both would end up with the
> same ctx->pos and end up updating f_pos to the same offset (assuming the
> same count).
> 
> Am I missing something?

A minimal and brute force approach to this would be to use
io_op_def.hash_reg_file, but brrr, that doesn't seem like a great way
forward.

Greetings,

Andres Freund