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 D8AB2FEC0F7 for ; Tue, 24 Mar 2026 18:57:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w56vp-0004ne-Ei; Tue, 24 Mar 2026 14:56:49 -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 1w56vk-0004kl-NI for qemu-devel@nongnu.org; Tue, 24 Mar 2026 14:56:45 -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 1w56vi-0006ga-0p for qemu-devel@nongnu.org; Tue, 24 Mar 2026 14:56:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774378601; 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: in-reply-to:in-reply-to:references:references; bh=gQ8AtBpJCcmriLtHU5b0J/GoC8msMoDc+3xdWz4LnAs=; b=BsMAW2zxNX6K1PxevMsy3KldhwgZu8RodYm3bpgrLFfEKCVECTvSjqmTf6V4co9ScqZ9J+ LhgRjhXmhsLKt6jXzK45TyhGV5MOwYdQcSTaSUPsZqleF8PiLStLQYGS07OggG9gyu1Rca kLeQtbnKtze87ynGwskvBTmquO8fxo4= Received: from mx-prod-mc-05.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-201-hEldPXqcPW2B0JOxpvPiOw-1; Tue, 24 Mar 2026 14:56:37 -0400 X-MC-Unique: hEldPXqcPW2B0JOxpvPiOw-1 X-Mimecast-MFC-AGG-ID: hEldPXqcPW2B0JOxpvPiOw_1774378596 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9F9CC19560A7; Tue, 24 Mar 2026 18:56:36 +0000 (UTC) Received: from merkur.fritz.box (unknown [10.44.33.246]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 836A5300019F; Tue, 24 Mar 2026 18:56:35 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [PULL 3/4] linux-aio: Resubmit tails of short reads/writes Date: Tue, 24 Mar 2026 19:56:18 +0100 Message-ID: <20260324185619.296946-4-kwolf@redhat.com> In-Reply-To: <20260324185619.296946-1-kwolf@redhat.com> References: <20260324185619.296946-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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: qemu development 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 From: Hanna Czenczek Short reads/writes can happen. One way to reproduce them is via our FUSE export, with the following diff applied (%s/escaped // to apply -- if you put plain diffs in commit messages, git-am will apply them, and I would rather avoid breaking FUSE accidentally via this patch): escaped diff --git a/block/export/fuse.c b/block/export/fuse.c escaped index a2a478d293..67dc50a412 100644 escaped --- a/block/export/fuse.c escaped +++ b/block/export/fuse.c @@ -828,7 +828,7 @@ static ssize_t coroutine_fn GRAPH_RDLOCK fuse_co_init(FuseExport *exp, struct fuse_init_out *out, const struct fuse_init_in_compat *in) { - const uint32_t supported_flags = FUSE_ASYNC_READ | FUSE_ASYNC_DIO; + const uint32_t supported_flags = FUSE_ASYNC_READ; if (in->major != 7) { error_report("FUSE major version mismatch: We have 7, but kernel has %" @@ -1060,6 +1060,8 @@ fuse_co_read(FuseExport *exp, void **bufptr, uint64_t offset, uint32_t size) void *buf; int ret; + size = MIN(size, 4096); + /* Limited by max_read, should not happen */ if (size > FUSE_MAX_READ_BYTES) { return -EINVAL; @@ -1110,6 +1112,8 @@ fuse_co_write(FuseExport *exp, struct fuse_write_out *out, int64_t blk_len; int ret; + size = MIN(size, 4096); + QEMU_BUILD_BUG_ON(FUSE_MAX_WRITE_BYTES > BDRV_REQUEST_MAX_BYTES); /* Limited by max_write, should not happen */ if (size > FUSE_MAX_WRITE_BYTES) { Then: $ ./qemu-img create -f raw test.raw 8k Formatting 'test.raw', fmt=raw size=8192 $ ./qemu-io -f raw -c 'write -P 42 0 8k' test.raw wrote 8192/8192 bytes at offset 0 8 KiB, 1 ops; 00.00 sec (64.804 MiB/sec and 8294.9003 ops/sec) $ hexdump -C test.raw 00000000 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************| * 00002000 With aio=threads, short I/O works: $ storage-daemon/qemu-storage-daemon \ --blockdev file,node-name=test,filename=test.raw \ --export fuse,id=exp,node-name=test,mountpoint=test.raw,writable=true Other shell: $ ./qemu-io --image-opts -c 'read -P 42 0 8k' \ driver=file,filename=test.raw,cache.direct=on,aio=threads read 8192/8192 bytes at offset 0 8 KiB, 1 ops; 00.00 sec (36.563 MiB/sec and 4680.0923 ops/sec) $ ./qemu-io --image-opts -c 'write -P 23 0 8k' \ driver=file,filename=test.raw,cache.direct=on,aio=threads wrote 8192/8192 bytes at offset 0 8 KiB, 1 ops; 00.00 sec (35.995 MiB/sec and 4607.2970 ops/sec) $ hexdump -C test.raw 00000000 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 |................| * 00002000 But with aio=native, it does not: $ ./qemu-io --image-opts -c 'read -P 23 0 8k' \ driver=file,filename=test.raw,cache.direct=on,aio=native Pattern verification failed at offset 0, 8192 bytes read 8192/8192 bytes at offset 0 8 KiB, 1 ops; 00.00 sec (86.155 MiB/sec and 11027.7900 ops/sec) $ ./qemu-io --image-opts -c 'write -P 42 0 8k' \ driver=file,filename=test.raw,cache.direct=on,aio=native write failed: No space left on device $ hexdump -C test.raw 00000000 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************| * 00001000 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 |................| * 00002000 This patch fixes that. Reviewed-by: Kevin Wolf Signed-off-by: Hanna Czenczek Message-ID: <20260324084338.37453-3-hreitz@redhat.com> Signed-off-by: Kevin Wolf --- block/linux-aio.c | 56 ++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 50 insertions(+), 6 deletions(-) diff --git a/block/linux-aio.c b/block/linux-aio.c index 3843f45eac8..0a7424fbb33 100644 --- a/block/linux-aio.c +++ b/block/linux-aio.c @@ -45,6 +45,10 @@ struct qemu_laiocb { size_t nbytes; QEMUIOVector *qiov; + /* For handling short reads/writes */ + size_t total_done; + QEMUIOVector resubmit_qiov; + int fd; int type; BdrvRequestFlags flags; @@ -74,28 +78,61 @@ struct LinuxAioState { }; static void ioq_submit(LinuxAioState *s); +static int laio_do_submit(struct qemu_laiocb *laiocb); static inline ssize_t io_event_ret(struct io_event *ev) { return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res); } +/** + * Retry tail of short requests. + */ +static int laio_resubmit_short_io(struct qemu_laiocb *laiocb, size_t done) +{ + QEMUIOVector *resubmit_qiov = &laiocb->resubmit_qiov; + + laiocb->total_done += done; + + if (!resubmit_qiov->iov) { + qemu_iovec_init(resubmit_qiov, laiocb->qiov->niov); + } else { + qemu_iovec_reset(resubmit_qiov); + } + qemu_iovec_concat(resubmit_qiov, laiocb->qiov, + laiocb->total_done, laiocb->nbytes - laiocb->total_done); + + return laio_do_submit(laiocb); +} + /* * Completes an AIO request. */ static void qemu_laio_process_completion(struct qemu_laiocb *laiocb) { - int ret; + ssize_t ret; ret = laiocb->ret; if (ret != -ECANCELED) { - if (ret == laiocb->nbytes) { + if (ret == laiocb->nbytes - laiocb->total_done) { ret = 0; + } else if (ret > 0 && (laiocb->type == QEMU_AIO_READ || + laiocb->type == QEMU_AIO_WRITE)) { + ret = laio_resubmit_short_io(laiocb, ret); + if (!ret) { + return; + } } else if (ret >= 0) { - /* Short reads mean EOF, pad with zeros. */ + /* + * For normal reads and writes, we only get here if ret == 0, which + * means EOF for reads and ENOSPC for writes. + * For zone-append, we get here with any ret >= 0, which we just + * treat as ENOSPC, too (safer than resubmitting, probably, but not + * 100 % clear). + */ if (laiocb->type == QEMU_AIO_READ) { - qemu_iovec_memset(laiocb->qiov, ret, 0, - laiocb->qiov->size - ret); + qemu_iovec_memset(laiocb->qiov, laiocb->total_done, 0, + laiocb->qiov->size - laiocb->total_done); } else { ret = -ENOSPC; } @@ -103,6 +140,9 @@ static void qemu_laio_process_completion(struct qemu_laiocb *laiocb) } laiocb->ret = ret; + if (laiocb->resubmit_qiov.iov) { + qemu_iovec_destroy(&laiocb->resubmit_qiov); + } /* * If the coroutine is already entered it must be in ioq_submit() and @@ -379,7 +419,11 @@ static int laio_do_submit(struct qemu_laiocb *laiocb) struct iocb *iocbs = &laiocb->iocb; QEMUIOVector *qiov = laiocb->qiov; int fd = laiocb->fd; - off_t offset = laiocb->offset; + off_t offset = laiocb->offset + laiocb->total_done; + + if (laiocb->resubmit_qiov.iov) { + qiov = &laiocb->resubmit_qiov; + } switch (laiocb->type) { case QEMU_AIO_WRITE: -- 2.53.0