linux-kernel - Re: [WTF] utterly tasteless ABI in hfi1 (around ->write()/->write

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Date:	Tue, 15 Mar 2016 21:34:03 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Mike Marciniszyn <infinipath@...el.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [WTF] utterly tasteless ABI in hfi1 (around ->write()/->write_iter())

On Tue, Mar 15, 2016 at 9:17 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
>         Take a look at drivers/staging/rdma/hfi1/file_ops.c in -next and
> compare hfi1_write_iter() with hfi1_file_write().  Folks, this ABI is too
> ugly to live, let alone to be allowed breeding.
>
>         It's also brittle as hell - trivial massage around fs/read_write.c
> and fs/aio.c is quite capable of breaking that shit.  Arguably, IOCB_CMD_PWRITE
> and IOCB_CMD_PWRITEV both triggering your writev() semantics is an example of
> just such breakage.  Sigh...

We could just decide that if a file descriptor has both ->write and
->write_iter entities, we always pick ->write_iter in the vfs layer.

That way it's always consistent.

Simple ordering change in __vfs_write()..

We can switch is back later, but make sure it hits a release or two.
Or at least a few rc's, to flush out any problems.

Anybody who thinks that they can have different semantics for write()
and writev() is just completely broken.

              Linus