From nobody Sun Feb 8 11:01:38 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.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; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com ARC-Seal: i=1; a=rsa-sha256; t=1564049188; cv=none; d=zoho.com; s=zohoarc; b=KcsWfWxsSFp7fRvqvYr8QOI+haGCp7IlEpTKrUAwE0M599qJxmrMGP+j1aBir1u2XiqGdL7Obhtx9GjEQNWxzPfW1kITzGS8LLqKIUWvy+v22Cp6M5/RkZAI+2PLoSNTyvacg54pFjuHkITN3esZTsVZQqPxGsu0b1GVTd1Bk9s= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1564049188; h=Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=ec4QhC0ARxECii/rZUpUgQc+5QfH8NoR443Fv+oQLmY=; b=RowKO3w34UNwpKAqsIp36/whiwiEUOf2bdgXRtpCWCjjmOr2lQRDT7Ev0doNVsK9rMqayP3mnrcFuSEObs3M08PyV//fTux0W6xhAU/KpOpJyZ+ZeYM5LZ03gDMfHp7moPmUF7N18GWDLHnl3JRQDnl8UuAnKpEo+jDrGo1PKyE= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 156404918821096.69422134425997; Thu, 25 Jul 2019 03:06:28 -0700 (PDT) Received: from localhost ([::1]:58310 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hqadj-0006Wp-Up for importer@patchew.org; Thu, 25 Jul 2019 06:06:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49297) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hqadN-0005WH-CN for qemu-devel@nongnu.org; Thu, 25 Jul 2019 06:06:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hqadJ-0006QP-QU for qemu-devel@nongnu.org; Thu, 25 Jul 2019 06:05:59 -0400 Received: from relay.sw.ru ([185.231.240.75]:45734) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hqadJ-0006O2-FE; Thu, 25 Jul 2019 06:05:57 -0400 Received: from [10.94.3.0] (helo=kvm.qa.sw.ru) by relay.sw.ru with esmtp (Exim 4.92) (envelope-from ) id 1hqadC-0001mQ-Tn; Thu, 25 Jul 2019 13:05:50 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-devel@nongnu.org, qemu-block@nongnu.org Date: Thu, 25 Jul 2019 13:05:48 +0300 Message-Id: <20190725100550.33801-2-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20190725100550.33801-1-vsementsov@virtuozzo.com> References: <20190725100550.33801-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v3 1/3] block: implement BDRV_REQ_PREFETCH X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, fam@euphon.net, vsementsov@virtuozzo.com, mreitz@redhat.com, stefanha@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Do effective copy-on-read request when we don't need data actually. It will be used for block-stream and NBD_CMD_CACHE. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Stefan Hajnoczi --- include/block/block.h | 8 +++++++- block/io.c | 18 ++++++++++++------ 2 files changed, 19 insertions(+), 7 deletions(-) diff --git a/include/block/block.h b/include/block/block.h index 50a07c1c33..73c3fc4daa 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -88,8 +88,14 @@ typedef enum { * fallback. */ BDRV_REQ_NO_FALLBACK =3D 0x100, =20 + /* + * BDRV_REQ_PREFETCH may be used only together with BDRV_REQ_COPY_ON_R= EAD + * on read request and means that caller don't really need data to be + * written to qiov parameter which may be NULL. + */ + BDRV_REQ_PREFETCH =3D 0x200, /* Mask of valid flags */ - BDRV_REQ_MASK =3D 0x1ff, + BDRV_REQ_MASK =3D 0x3ff, } BdrvRequestFlags; =20 typedef struct BlockSizes { diff --git a/block/io.c b/block/io.c index 06305c6ea6..9d99858b55 100644 --- a/block/io.c +++ b/block/io.c @@ -1167,7 +1167,8 @@ bdrv_driver_pwritev_compressed(BlockDriverState *bs, = uint64_t offset, } =20 static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child, - int64_t offset, unsigned int bytes, QEMUIOVector *qiov) + int64_t offset, unsigned int bytes, QEMUIOVector *qiov, + int flags) { BlockDriverState *bs =3D child->bs; =20 @@ -1278,9 +1279,11 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(Bdr= vChild *child, goto err; } =20 - qemu_iovec_from_buf(qiov, progress, bounce_buffer + skip_bytes, - pnum - skip_bytes); - } else { + if (!(flags & BDRV_REQ_PREFETCH)) { + qemu_iovec_from_buf(qiov, progress, bounce_buffer + skip_b= ytes, + pnum - skip_bytes); + } + } else if (!(flags & BDRV_REQ_PREFETCH)) { /* Read directly into the destination */ qemu_iovec_init(&local_qiov, qiov->niov); qemu_iovec_concat(&local_qiov, qiov, progress, pnum - skip_byt= es); @@ -1331,7 +1334,8 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild= *child, * potential fallback support, if we ever implement any read flags * to pass through to drivers. For now, there aren't any * passthrough flags. */ - assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ))); + assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ | + BDRV_REQ_PREFETCH))); =20 /* Handle Copy on Read and associated serialisation */ if (flags & BDRV_REQ_COPY_ON_READ) { @@ -1359,7 +1363,9 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild= *child, } =20 if (!ret || pnum !=3D bytes) { - ret =3D bdrv_co_do_copy_on_readv(child, offset, bytes, qiov); + ret =3D bdrv_co_do_copy_on_readv(child, offset, bytes, qiov, f= lags); + goto out; + } else if (flags & BDRV_REQ_PREFETCH) { goto out; } } --=20 2.18.0 From nobody Sun Feb 8 11:01:38 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.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; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com ARC-Seal: i=1; a=rsa-sha256; t=1564049205; cv=none; d=zoho.com; s=zohoarc; b=KdI/BUMVA8QUxAOGbZ6/AZ3vETLYIUHhDCFHo2qhkZ3s4kvi1fXjT8WrVgqDchV5bIB4lNH6sKMMIwU80LXnVNZF65NNl+A40vL9Yf7t3INVG0trgB9IoKEjdUWeCMMFPPLHgkUhG7UKCMgdwG0C9RHI7+skNA6W1TzCWwDltx8= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1564049205; h=Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=VhLurBfsSD8JMJS1ixodg6vxUOswNjz4RlbiaTFNMW0=; b=EliqkbVWYzHnPE0gpm00ap1Lj3KvhSO+UbGiJmmu2v3U0cDZZBDEXLW6Th/nqDFqq0b0Z3KL03mfq25aN03rtZKSNyAVJKFmUZsRcRi03YsUPBfbTEIxwOZasRXI7osv952Em99Q6AOmDEKdP2iM7zV9bI+W7Ykr/VUJHypFtag= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1564049205965925.4767469658682; Thu, 25 Jul 2019 03:06:45 -0700 (PDT) Received: from localhost ([::1]:58324 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hqae4-00085Z-Qa for importer@patchew.org; Thu, 25 Jul 2019 06:06:44 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49296) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hqadN-0005WG-CF for qemu-devel@nongnu.org; Thu, 25 Jul 2019 06:06:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hqadJ-0006Q6-Mj for qemu-devel@nongnu.org; Thu, 25 Jul 2019 06:05:59 -0400 Received: from relay.sw.ru ([185.231.240.75]:45720) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hqadI-0006O1-7y; Thu, 25 Jul 2019 06:05:57 -0400 Received: from [10.94.3.0] (helo=kvm.qa.sw.ru) by relay.sw.ru with esmtp (Exim 4.92) (envelope-from ) id 1hqadC-0001mQ-Vy; Thu, 25 Jul 2019 13:05:51 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-devel@nongnu.org, qemu-block@nongnu.org Date: Thu, 25 Jul 2019 13:05:49 +0300 Message-Id: <20190725100550.33801-3-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20190725100550.33801-1-vsementsov@virtuozzo.com> References: <20190725100550.33801-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v3 2/3] block/stream: use BDRV_REQ_PREFETCH X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, fam@euphon.net, vsementsov@virtuozzo.com, mreitz@redhat.com, stefanha@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" This helps to avoid extra io, allocations and memory copying. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Stefan Hajnoczi --- block/stream.c | 20 +++++++------------- 1 file changed, 7 insertions(+), 13 deletions(-) diff --git a/block/stream.c b/block/stream.c index 6ac1e7bec4..170e3b43be 100644 --- a/block/stream.c +++ b/block/stream.c @@ -22,11 +22,11 @@ =20 enum { /* - * Size of data buffer for populating the image file. This should be = large + * Maximum chunk size to feed it to copy-on-read. This should be large * enough to process multiple clusters in a single call, so that popul= ating * contiguous regions of the image is efficient. */ - STREAM_BUFFER_SIZE =3D 512 * 1024, /* in bytes */ + STREAM_CHUNK =3D 512 * 1024, /* in bytes */ }; =20 typedef struct StreamBlockJob { @@ -39,13 +39,12 @@ typedef struct StreamBlockJob { } StreamBlockJob; =20 static int coroutine_fn stream_populate(BlockBackend *blk, - int64_t offset, uint64_t bytes, - void *buf) + int64_t offset, uint64_t bytes) { assert(bytes < SIZE_MAX); =20 - /* Copy-on-read the unallocated clusters */ - return blk_co_pread(blk, offset, bytes, buf, BDRV_REQ_COPY_ON_READ); + return blk_co_preadv(blk, offset, bytes, NULL, + BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH); } =20 static void stream_abort(Job *job) @@ -117,7 +116,6 @@ static int coroutine_fn stream_run(Job *job, Error **er= rp) int error =3D 0; int ret =3D 0; int64_t n =3D 0; /* bytes */ - void *buf; =20 if (bs =3D=3D s->bottom) { /* Nothing to stream */ @@ -130,8 +128,6 @@ static int coroutine_fn stream_run(Job *job, Error **er= rp) } job_progress_set_remaining(&s->common.job, len); =20 - buf =3D qemu_blockalign(bs, STREAM_BUFFER_SIZE); - /* Turn on copy-on-read for the whole block device so that guest read * requests help us make progress. Only do this when copying the enti= re * backing chain since the copy-on-read operation does not take base i= nto @@ -154,7 +150,7 @@ static int coroutine_fn stream_run(Job *job, Error **er= rp) =20 copy =3D false; =20 - ret =3D bdrv_is_allocated(bs, offset, STREAM_BUFFER_SIZE, &n); + ret =3D bdrv_is_allocated(bs, offset, STREAM_CHUNK, &n); if (ret =3D=3D 1) { /* Allocated in the top, no need to copy. */ } else if (ret >=3D 0) { @@ -171,7 +167,7 @@ static int coroutine_fn stream_run(Job *job, Error **er= rp) } trace_stream_one_iteration(s, offset, n, ret); if (copy) { - ret =3D stream_populate(blk, offset, n, buf); + ret =3D stream_populate(blk, offset, n); } if (ret < 0) { BlockErrorAction action =3D @@ -202,8 +198,6 @@ static int coroutine_fn stream_run(Job *job, Error **er= rp) bdrv_disable_copy_on_read(bs); } =20 - qemu_vfree(buf); - /* Do not remove the backing file if an error was there but ignored. */ return error; } --=20 2.18.0 From nobody Sun Feb 8 11:01:38 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.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; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com ARC-Seal: i=1; a=rsa-sha256; t=1564049225; cv=none; d=zoho.com; s=zohoarc; b=h+2QhvABuSeeALYwCEMJodREj/CdlbtSOw3UXxWBKfyKi+p3Cv4dcJCB8LOs+blmB2GdV/UoeGrQoikNOvcV6/cCLwdmVZDJlUEZXyKouD/2xl74J0ll/ZIw8Cp4B03EWKr7Y7zEOaHl0LX7Y+fzNr/avc4NB1gRNmQaLNZNSK8= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1564049225; h=Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=7N4cBy560YX4ew4fx2oWhmG31f1kwi/bQIbFWKjOwx4=; b=Gly6zYLnG0jn9bfVqLxnsy7ZA53ybTmyBwtApiqFlxxZcIIzMpJJiU8+HOCwif6guBCo9COrY2xjGbXmqDeSK37G7w25Qs3EG8t2q1hI1b86xdokUPTvx9YqmxzDRQGck6/h+o7FXnhZRi7d32nM01zPGFVCy7HJGsFyTlhrKxk= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1564049225148394.1059009915325; Thu, 25 Jul 2019 03:07:05 -0700 (PDT) Received: from localhost ([::1]:58334 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hqaeO-0000wn-2i for importer@patchew.org; Thu, 25 Jul 2019 06:07:04 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49320) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hqadO-0005WJ-9D for qemu-devel@nongnu.org; Thu, 25 Jul 2019 06:06:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hqadN-0006R5-65 for qemu-devel@nongnu.org; Thu, 25 Jul 2019 06:06:02 -0400 Received: from relay.sw.ru ([185.231.240.75]:45726) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hqadJ-0006O5-JR; Thu, 25 Jul 2019 06:05:57 -0400 Received: from [10.94.3.0] (helo=kvm.qa.sw.ru) by relay.sw.ru with esmtp (Exim 4.92) (envelope-from ) id 1hqadD-0001mQ-2y; Thu, 25 Jul 2019 13:05:51 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-devel@nongnu.org, qemu-block@nongnu.org Date: Thu, 25 Jul 2019 13:05:50 +0300 Message-Id: <20190725100550.33801-4-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20190725100550.33801-1-vsementsov@virtuozzo.com> References: <20190725100550.33801-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v3 3/3] nbd: improve CMD_CACHE: use BDRV_REQ_PREFETCH X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, fam@euphon.net, vsementsov@virtuozzo.com, mreitz@redhat.com, stefanha@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" This helps to avoid extra io, allocations and memory copying. We assume here that CMD_CACHE is always used with copy-on-read, as otherwise it's a noop. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Eric Blake Reviewed-by: Stefan Hajnoczi --- nbd/server.c | 43 +++++++++++++++++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 8 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index 10faedcfc5..a2cf085f76 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -2104,12 +2104,15 @@ static int nbd_co_receive_request(NBDRequestData *r= eq, NBDRequest *request, return -EINVAL; } =20 - req->data =3D blk_try_blockalign(client->exp->blk, request->len); - if (req->data =3D=3D NULL) { - error_setg(errp, "No memory"); - return -ENOMEM; + if (request->type !=3D NBD_CMD_CACHE) { + req->data =3D blk_try_blockalign(client->exp->blk, request->le= n); + if (req->data =3D=3D NULL) { + error_setg(errp, "No memory"); + return -ENOMEM; + } } } + if (request->type =3D=3D NBD_CMD_WRITE) { if (nbd_read(client->ioc, req->data, request->len, "CMD_WRITE data= ", errp) < 0) @@ -2194,7 +2197,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *cl= ient, NBDRequest *request, int ret; NBDExport *exp =3D client->exp; =20 - assert(request->type =3D=3D NBD_CMD_READ || request->type =3D=3D NBD_C= MD_CACHE); + assert(request->type =3D=3D NBD_CMD_READ); =20 /* XXX: NBD Protocol only documents use of FUA with WRITE */ if (request->flags & NBD_CMD_FLAG_FUA) { @@ -2206,7 +2209,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *cl= ient, NBDRequest *request, } =20 if (client->structured_reply && !(request->flags & NBD_CMD_FLAG_DF) && - request->len && request->type !=3D NBD_CMD_CACHE) + request->len) { return nbd_co_send_sparse_read(client, request->handle, request->f= rom, data, request->len, errp); @@ -2214,7 +2217,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *cl= ient, NBDRequest *request, =20 ret =3D blk_pread(exp->blk, request->from + exp->dev_offset, data, request->len); - if (ret < 0 || request->type =3D=3D NBD_CMD_CACHE) { + if (ret < 0) { return nbd_send_generic_reply(client, request->handle, ret, "reading from file failed", errp); } @@ -2233,6 +2236,28 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *c= lient, NBDRequest *request, } } =20 +/* + * nbd_do_cmd_cache + * + * Handle NBD_CMD_CACHE request. + * Return -errno if sending fails. Other errors are reported directly to t= he + * client as an error reply. + */ +static coroutine_fn int nbd_do_cmd_cache(NBDClient *client, NBDRequest *re= quest, + Error **errp) +{ + int ret; + NBDExport *exp =3D client->exp; + + assert(request->type =3D=3D NBD_CMD_CACHE); + + ret =3D blk_co_preadv(exp->blk, request->from + exp->dev_offset, reque= st->len, + NULL, BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH); + + return nbd_send_generic_reply(client, request->handle, ret, + "caching data failed", errp); +} + /* Handle NBD request. * Return -errno if sending fails. Other errors are reported directly to t= he * client as an error reply. */ @@ -2246,8 +2271,10 @@ static coroutine_fn int nbd_handle_request(NBDClient= *client, char *msg; =20 switch (request->type) { - case NBD_CMD_READ: case NBD_CMD_CACHE: + return nbd_do_cmd_cache(client, request, errp); + + case NBD_CMD_READ: return nbd_do_cmd_read(client, request, data, errp); =20 case NBD_CMD_WRITE: --=20 2.18.0