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Tue, 20 Dec 2022 03:42:55 -0500 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-668-l6acZj49OqqQwbBFeq3E4w-1; Tue, 20 Dec 2022 03:42:49 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C129B1C08970; Tue, 20 Dec 2022 08:42:48 +0000 (UTC) Received: from sirius.home.kraxel.org (unknown [10.39.192.110]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7B8E839D6D; Tue, 20 Dec 2022 08:42:48 +0000 (UTC) Received: by sirius.home.kraxel.org (Postfix, from userid 1000) id C719C18000B3; Tue, 20 Dec 2022 09:42:46 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671525772; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=IQTYlT7DKteIN7LPObgobrwFgEFxgjatjVEatFARAE0=; b=LvgHJCueFHfsfsFheDdQslHhJGafD9Furx+tQF9bfrhv+/G0wZNL6edACJEM9HdW3OxTKL OL5Z9XOiiveJdoYuU6z0h58MvBqaeHQksRi9boPleFB1QmmTFlHlWf3dhLwPYytpco+Z9e itP1J5pnu8tgHTrG+UzR/g2ki54eQJw= X-MC-Unique: l6acZj49OqqQwbBFeq3E4w-1 From: Gerd Hoffmann To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Kevin Wolf , Peter Maydell , qemu-arm@nongnu.org, Hanna Reitz , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , John Snow , Kashyap Chamarthy , Xiang Zheng , Gerd Hoffmann Subject: [PATCH v2] pflash: Only read non-zero parts of backend image Date: Tue, 20 Dec 2022 09:42:46 +0100 Message-Id: <20221220084246.1984871-1-kraxel@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=kraxel@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_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1671525820769100011 Content-Type: text/plain; charset="utf-8" From: Xiang Zheng Currently we fill the VIRT_FLASH memory space with two 64MB NOR images when using persistent UEFI variables on virt board. Actually we only use a very small(non-zero) part of the memory while the rest significant large(zero) part of memory is wasted. So this patch checks the block status and only writes the non-zero part into memory. This requires pflash devices to use sparse files for backends. Signed-off-by: Xiang Zheng [ kraxel: rebased to latest master ] Signed-off-by: Gerd Hoffmann Reviewed-by: Daniel P. Berrang=C3=A9 --- hw/block/block.c | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) diff --git a/hw/block/block.c b/hw/block/block.c index f9c4fe67673b..142ebe4267e4 100644 --- a/hw/block/block.c +++ b/hw/block/block.c @@ -14,6 +14,40 @@ #include "qapi/error.h" #include "qapi/qapi-types-block.h" =20 +/* + * Read the non-zeroes parts of @blk into @buf + * Reading all of the @blk is expensive if the zeroes parts of @blk + * is large enough. Therefore check the block status and only write + * the non-zeroes block into @buf. + * + * Return 0 on success, non-zero on error. + */ +static int blk_pread_nonzeroes(BlockBackend *blk, hwaddr size, void *buf) +{ + int ret; + int64_t bytes, offset =3D 0; + BlockDriverState *bs =3D blk_bs(blk); + + for (;;) { + bytes =3D MIN(size - offset, BDRV_REQUEST_MAX_SECTORS); + if (bytes <=3D 0) { + return 0; + } + ret =3D bdrv_block_status(bs, offset, bytes, &bytes, NULL, NULL); + if (ret < 0) { + return ret; + } + if (!(ret & BDRV_BLOCK_ZERO)) { + ret =3D bdrv_pread(bs->file, offset, bytes, + (uint8_t *) buf + offset, 0); + if (ret < 0) { + return ret; + } + } + offset +=3D bytes; + } +} + /* * Read the entire contents of @blk into @buf. * @blk's contents must be @size bytes, and @size must be at most @@ -53,7 +87,7 @@ bool blk_check_size_and_read_all(BlockBackend *blk, void = *buf, hwaddr size, * block device and read only on demand. */ assert(size <=3D BDRV_REQUEST_MAX_BYTES); - ret =3D blk_pread(blk, 0, size, buf, 0); + ret =3D blk_pread_nonzeroes(blk, size, buf); if (ret < 0) { error_setg_errno(errp, -ret, "can't read block backend"); return false; --=20 2.38.1