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Re: [Qemu-block] [PATCH] blockdev: warn about aio=native if libaio is un
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [PATCH] blockdev: warn about aio=native if libaio is unavailable |
Date: |
Fri, 17 Jul 2015 12:56:15 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 17.07.2015 um 11:59 hat Stefan Hajnoczi geschrieben:
> QEMU silently ignores aio=native if libaio is unavailable. It is
> confusing when aio=native performance is identical to aio=threads
> because the binary was accidentally built without libaio.
>
> Use error_report() because failing would break backward compatibility.
> There are probably users using aio=native who would be inconvenienced if
> QEMU suddenly refused to start their guests.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
I hope not too many people are using aio=native without having libaio
compiled in... Can we make it a message like for the case with
aio=native,cache.direct=off, i.e. a deprecation warning that allows us
to make this an error in a few releases?
> blockdev.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index 62a4586..f30828a 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -405,10 +405,14 @@ static BlockBackend *blockdev_init(const char *file,
> QDict *bs_opts,
> bdrv_flags |= BDRV_O_NO_FLUSH;
> }
>
> -#ifdef CONFIG_LINUX_AIO
> if ((buf = qemu_opt_get(opts, "aio")) != NULL) {
> if (!strcmp(buf, "native")) {
> +#ifdef CONFIG_LINUX_AIO
> bdrv_flags |= BDRV_O_NATIVE_AIO;
> +#else
> + error_report("warning: aio=native support unavailable, "
> + "using default instead");
> +#endif
> } else if (!strcmp(buf, "threads")) {
> /* this is the default */
> } else {
> @@ -416,7 +420,6 @@ static BlockBackend *blockdev_init(const char *file,
> QDict *bs_opts,
> goto early_err;
> }
> }
> -#endif
*sigh* It's sad to see that we still have such code in the generic block
layer. It has no business there, the raw-posix driver should check
whether it can support Linux AIO or not.
Paolo: You added some code to raw-win32 that implements aio=native.
Did it ever work in qemu proper, or only in the tools? It doesn't seem
that this code would even have added the flag on Windows builds.
Kevin