linux-kernel - Re: [V9fs-developer] [PATCH] fs: 9p: add generic splice

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Message-ID: <87mtyx1rem.fsf@toke.dk>
Date:   Tue, 01 Dec 2020 16:23:45 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Eric Van Hensbergen <ericvh@...il.com>,
        Latchesar Ionkov <lucho@...kov.net>,
        linux-kernel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net
Subject: Re: [V9fs-developer] [PATCH] fs: 9p: add generic splice_read file
 operations

Dominique Martinet <asmadeus@...ewreck.org> writes:

> Dominique Martinet wrote on Tue, Dec 01, 2020:
>> > Since generic_file_splice_read() seems to just implement splice_read in
>> > terms of the read_iter operation, I simply added the generic implementation
>> > to the file operations, which fixed the error I was seeing. A quick grep
>> > indicates that this is what most other file systems do as well.
>> 
>> Good catch, might as well do that.
>> I'm surprised you didn't hit the same problem with splice_write?
>> 
>> I see iter_file_splice_write being used for it on many filesystems,
>> it's probably better to add both?
>
> Yeah, I confirm both are needed (the second for the pipe -> fs side)

Yeah, makes sense; I was only testing with a very specific use case
where a file is being passed to the kernel with sendfile().

> This made me test copy_file_range, and it works with both as well (used
> not to)
>
> interestingly on older kernels this came as default somehow? I have
> splice working on 5.4.67 :/ so this broke somewhat recently...

Huh, no idea; this is my first time digging into filesystem code, I
normally do networking and BPF :)

> I'll add an extra patch with the second and take your patch.
> Thanks!

Awesome, thanks!

-Toke