From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 052DDC369A2 for ; Mon, 14 Apr 2025 15:35:59 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u4LqD-0005n9-Eb; Mon, 14 Apr 2025 11:35:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u4Lq1-0005ih-Hr for qemu-devel@nongnu.org; Mon, 14 Apr 2025 11:35:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u4Lpz-0006ru-6j for qemu-devel@nongnu.org; Mon, 14 Apr 2025 11:35:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744644904; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=pTtdttDpMRCIR7RfY29Gl2AoWEWL6IbplTk10NoHapc=; b=ZHX09ltNl6K8uceai+coCjYTi5VTQibGtNIHWZDkC5d0Qk1Fu/APp/6cG1H0zfnWnFvxNl u2cPwevncJc4NRGJMUGzPo2Gn/uaqhd9mHsRNzUJUIDdPKY7PI6hdN3IwMD1v2MrY8Du8N LNvgnS1x6lltgIL+fTYMfWJEWzuTJyA= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-237-rvIazJjVOxOkS6crMzGRuw-1; Mon, 14 Apr 2025 11:34:56 -0400 X-MC-Unique: rvIazJjVOxOkS6crMzGRuw-1 X-Mimecast-MFC-AGG-ID: rvIazJjVOxOkS6crMzGRuw_1744644895 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E899F1954B36; Mon, 14 Apr 2025 15:34:53 +0000 (UTC) Received: from localhost (unknown [10.2.16.100]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 03AA91828AAA; Mon, 14 Apr 2025 15:34:52 +0000 (UTC) Date: Mon, 14 Apr 2025 11:34:51 -0400 From: Stefan Hajnoczi To: Hanna Czenczek Cc: qemu-devel@nongnu.org, Kevin Wolf , Fam Zheng , qemu-block@nongnu.org Subject: Re: [PATCH v2 1/2] file-posix: probe discard alignment on Linux block devices Message-ID: <20250414153451.GC117758@fedora> References: <20250410184103.23385-1-stefanha@redhat.com> <20250410184103.23385-2-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="cFhVdxoYEyX1w5mf" Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --cFhVdxoYEyX1w5mf Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Apr 11, 2025 at 10:15:13AM +0200, Hanna Czenczek wrote: > On 10.04.25 20:41, Stefan Hajnoczi wrote: > > Populate the pdiscard_alignment block limit so the block layer is able > > align discard requests correctly. > >=20 > > Signed-off-by: Stefan Hajnoczi > > --- > > block/file-posix.c | 56 +++++++++++++++++++++++++++++++++++++++++++++- > > 1 file changed, 55 insertions(+), 1 deletion(-) >=20 > Ah, I didn=E2=80=99t know sysfs is actually fair game.=C2=A0 Should we no= t also get the > maximum discard length then, too? The maximum discard length behaves differently: the Linux block layer splits requests according to the maximum discard length. If the guest submits a discard request that is too large for the host, the host block layer will split it and the request succeeds. That is why I didn't make any changes to the maximum discard length in this series. >=20 > > diff --git a/block/file-posix.c b/block/file-posix.c > > index 56d1972d15..2a1e1f48c0 100644 > > --- a/block/file-posix.c > > +++ b/block/file-posix.c > > @@ -1276,10 +1276,10 @@ static int get_sysfs_zoned_model(struct stat *s= t, BlockZoneModel *zoned) > > } > > #endif /* defined(CONFIG_BLKZONED) */ > > +#ifdef CONFIG_LINUX > > /* > > * Get a sysfs attribute value as a long integer. > > */ > > -#ifdef CONFIG_LINUX > > static long get_sysfs_long_val(struct stat *st, const char *attribute) > > { > > g_autofree char *str =3D NULL; > > @@ -1299,6 +1299,30 @@ static long get_sysfs_long_val(struct stat *st, = const char *attribute) > > } > > return ret; > > } > > + > > +/* > > + * Get a sysfs attribute value as a uint32_t. > > + */ > > +static int get_sysfs_u32_val(struct stat *st, const char *attribute, > > + uint32_t *u32) > > +{ > > + g_autofree char *str =3D NULL; > > + const char *end; > > + unsigned int val; > > + int ret; > > + > > + ret =3D get_sysfs_str_val(st, attribute, &str); > > + if (ret < 0) { > > + return ret; > > + } > > + > > + /* The file is ended with '\n', pass 'end' to accept that. */ > > + ret =3D qemu_strtoui(str, &end, 10, &val); > > + if (ret =3D=3D 0 && end && *end =3D=3D '\0') { > > + *u32 =3D val; > > + } > > + return ret; > > +} > > #endif > > static int hdev_get_max_segments(int fd, struct stat *st) > > @@ -1318,6 +1342,23 @@ static int hdev_get_max_segments(int fd, struct = stat *st) > > #endif > > } > > +/* > > + * Fills in *dalign with the discard alignment and returns 0 on succes= s, > > + * -errno otherwise. > > + */ > > +static int hdev_get_pdiscard_alignment(struct stat *st, uint32_t *dali= gn) > > +{ > > +#ifdef CONFIG_LINUX > > + /* > > + * Note that Linux "discard_granularity" is QEMU "discard_alignmen= t". Linux > > + * "discard_alignment" is something else. > > + */ > > + return get_sysfs_u32_val(st, "discard_granularity", dalign); > > +#else > > + return -ENOTSUP; > > +#endif > > +} > > + > > #if defined(CONFIG_BLKZONED) > > /* > > * If the reset_all flag is true, then the wps of zone whose state is > > @@ -1527,6 +1568,19 @@ static void raw_refresh_limits(BlockDriverState = *bs, Error **errp) > > } > > } > > + if (S_ISBLK(st.st_mode)) { > > + uint32_t dalign =3D 0; > > + int ret; > > + > > + ret =3D hdev_get_pdiscard_alignment(&st, &dalign); > > + if (ret =3D=3D 0) { > > + /* Must be a multiple of request_alignment */ > > + assert(dalign % bs->bl.request_alignment =3D=3D 0); >=20 > Is it fair to crash qemu if the kernel reports a value that is not a > multiple of request_alignment?=C2=A0 Wouldn=E2=80=99t it make more sense = to take the > maximum, and if that still isn=E2=80=99t a multiple, return an error here? I'll replace the assertion with an error. The Linux block layer sysfs documentation says: [RO] Devices that support discard functionality may internally allocate space using units that are bigger than the logical block size. I don't expect dalign to be smaller than request_alignment, but it doesn't hurt the check if request_alignment would work. >=20 > Hanna >=20 > > + > > + bs->bl.pdiscard_alignment =3D dalign; > > + } > > + } > > + > > raw_refresh_zoned_limits(bs, &st, errp); > > } >=20 --cFhVdxoYEyX1w5mf Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmf9KxsACgkQnKSrs4Gr c8jPnQf8D1+1twXgXGCJABQ3O0xx3wX4AE1mK/MZwqCaece9Re1CHKo++NahrrjK wY9wAwTrL6kzJpE/nyRoH/2zJvsx23w0vCKoqaOtyFuGUzLF8SFTkfHs01t2ezSv iQaQz4l6H7K3cgRyD5uw72z/kqDEcDWKLGnGkWIOI/Exag8h8VDvOiP4tk7cNezi bGvvHCjyUnQYxsKvAyRpZx46X8HtyvK+jRWbJ++JvuvlOnysUxR2lMfqmEZfV03g vT0NDt0xIDdcfLxRltEBOrFeLjzXtOAFC21EWv1WwUv41jMU7jI4r7ywXJW9+hz1 DKO71EE8m7/22mDkOXCCHjOKhvQlDQ== =QbKK -----END PGP SIGNATURE----- --cFhVdxoYEyX1w5mf--