linux-ext4 - Re: [RFC 0/7] io

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Date:   Wed, 26 Jul 2023 15:22:03 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Hao Xu <hao.xu@...ux.dev>
Cc:     io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Pavel Begunkov <asml.silence@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [RFC 0/7] io_uring lseek

On Wed, Jul 26, 2023 at 06:25:56PM +0800, Hao Xu wrote:
> From: Hao Xu <howeyxu@...cent.com>
> 
> This series adds lseek for io_uring, the motivation to import this
> syscall is in previous io_uring getdents patchset, we lack a way to
> rewind the file cursor when it goes to the end of file. Another reason
> is lseek is a common syscall, it's good for coding consistency when
> users use io_uring as their main loop.

While I understand this it is a time consuming review to make sure
things work correctly. So before we get this thing going we better get
getdents correct first.

> 
> Patch 1 is code clean for iomap
> Patch 2 adds IOMAP_NOWAIT logic for iomap lseek
> Patch 3 adds a nowait parameter to for IOMAP_NOWAIT control
> Patch 4 adds llseek_nowait() for file_operations so that specific
>         filesystem can implement it for nowait lseek
> Patch 5 adds llseek_nowait() implementation for xfs
> Patch 6 adds a new vfs wrapper for io_uring use
> Patch 7 is the main io_uring lseek implementation
> 
> Note, this series depends on the previous io_uring getdents series.
> 
> This is marked RFC since there is (at least) an issue to be discussed:
> The work in this series is mainly to reslove a problem that the current
> llseek() in struct file_operations doesn't have a place to deliver
> nowait info, and adding an argument to it results in update for llseek
> implementation of all filesystems (35 functions), so here I introduce
> a new llseek_nowait() as a workaround.

My intuition would be to update all filesystems. Adding new inode
operations always starts as a temporary thing and then we live with two
different methods for the next years or possibly forever.

But it'd be good to hear what others think.