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From: Stefan Hajnoczi <stefanha@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Fam Zheng <fam@euphon.net>,
	oleksandr@redhat.com, qemu-block@nongnu.org,
	Markus Armbruster <armbru@redhat.com>,
	Julia Suvorova <jusual@redhat.com>,
	qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Aarushi Mehta <mehta.aaru20@gmail.com>
Subject: Re: [PATCH v2 05/15] stubs: add stubs for io_uring interface
Date: Tue, 3 Dec 2019 11:16:00 +0000	[thread overview]
Message-ID: <20191203111600.GA167235@stefanha-x1.localdomain> (raw)
In-Reply-To: <20191111111347.GC7297@linux.fritz.box>

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On Mon, Nov 11, 2019 at 12:13:47PM +0100, Kevin Wolf wrote:
> Am 25.10.2019 um 18:04 hat Stefan Hajnoczi geschrieben:
> > From: Aarushi Mehta <mehta.aaru20@gmail.com>
> > 
> > Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> This commit message needs to answer at least where these stubs are
> actually used. Aren't all callers protected with #ifdef
> CONFIG_LINUX_IO_URING? (And if they aren't, why is abort() okay?)

Okay, I'll clarify in the commit description.

I didn't find a program that actually requires these stubs today, but in
theory they are required when:
1. A program links against util-obj-y but not block-obj-y (e.g.
   vhost-user-gpu)
AND
2. It uses util/async.o, which depends on luring_*() APIs

You can test this by adding a call to qemu_bh_new() into
vhost-user-gpu's main.c:

  ld: libqemuutil.a(async.o): in function `aio_ctx_finalize':
  qemu/util/async.c:281: undefined reference to `luring_detach_aio_context'
  ld: /home/stefanha/qemu/util/async.c:282: undefined reference to `luring_cleanup'
  ld: libqemuutil.a(async.o): in function `aio_setup_linux_io_uring':
  qemu/util/async.c:358: undefined reference to `luring_init'
  ld: /home/stefanha/qemu/util/async.c:363: undefined reference to `luring_attach_aio_context'

The program may have no intention of using io_uring, just the QEMU main
loop and BH, so there is an argument for avoiding linking block-obj-y*.
That's the purpose of the stubs and why abort() is okay.

* It's possible to argue against this and personally I'm not that
convinced by stubs for this scenario.  But io_uring.o should be
consistent with how things work today with linux-aio.o.  If you feel
strongly against having stubs then the linux-aio.o stubs should also be
removed (see commit c2b38b277a788).

Stefan

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  parent reply	other threads:[~2019-12-03 11:31 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-25 16:04 [PATCH v2 00/15] io_uring: add Linux io_uring AIO engine Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 01/15] configure: permit use of io_uring Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 02/15] qapi/block-core: add option for io_uring Stefan Hajnoczi
2019-10-25 19:09   ` Markus Armbruster
2019-10-25 16:04 ` [PATCH v2 03/15] block/block: add BDRV flag " Stefan Hajnoczi
2019-11-11 10:57   ` Kevin Wolf
2019-11-11 16:25     ` Max Reitz
2019-11-13 11:42       ` Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 04/15] block/io_uring: implements interfaces " Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 05/15] stubs: add stubs for io_uring interface Stefan Hajnoczi
2019-11-11 11:13   ` Kevin Wolf
2019-11-13 11:42     ` Stefan Hajnoczi
2019-12-03 11:16     ` Stefan Hajnoczi [this message]
2019-12-03 14:28       ` Kevin Wolf
2019-12-03 15:55         ` Paolo Bonzini
2019-10-25 16:04 ` [PATCH v2 06/15] util/async: add aio interfaces for io_uring Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 07/15] blockdev: adds bdrv_parse_aio to use io_uring Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 08/15] block/file-posix.c: extend " Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 09/15] block: add trace events for io_uring Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 10/15] block/io_uring: adds userspace completion polling Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 11/15] qemu-io: adds option to use aio engine Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 12/15] qemu-img: adds option to use aio engine for benchmarking Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 13/15] qemu-nbd: adds option for aio engines Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 14/15] tests/qemu-iotests: enable testing with aio options Stefan Hajnoczi
2019-10-25 16:04 ` [PATCH v2 15/15] tests/qemu-iotests: use AIOMODE with various tests Stefan Hajnoczi
2019-11-04 10:32 ` [PATCH v2 00/15] io_uring: add Linux io_uring AIO engine Stefan Hajnoczi
2019-11-13 11:43   ` Stefan Hajnoczi

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