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 X-Spam-Level: X-Spam-Status: No, score=-17.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A582CC4338F for ; Wed, 18 Aug 2021 05:46:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DC2D61029 for ; Wed, 18 Aug 2021 05:46:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237812AbhHRFr2 (ORCPT ); Wed, 18 Aug 2021 01:47:28 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:46656 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237788AbhHRFr1 (ORCPT ); Wed, 18 Aug 2021 01:47:27 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Ujd4jSh_1629265611; Received: from admindeMacBook-Pro-2.local(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0Ujd4jSh_1629265611) by smtp.aliyun-inc.com(127.0.0.1); Wed, 18 Aug 2021 13:46:51 +0800 Subject: Re: [Virtio-fs] [virtiofsd PATCH v4 4/4] virtiofsd: support per-file DAX in FUSE_LOOKUP To: "Dr. David Alan Gilbert" Cc: vgoyal@redhat.com, stefanha@redhat.com, miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, virtio-fs@redhat.com, joseph.qi@linux.alibaba.com, virtualization@lists.linux-foundation.org References: <20210817022220.17574-1-jefflexu@linux.alibaba.com> <20210817022347.18098-1-jefflexu@linux.alibaba.com> <20210817022347.18098-5-jefflexu@linux.alibaba.com> From: JeffleXu Message-ID: <29627110-e4bf-836f-2343-1faeb36ad4d3@linux.alibaba.com> Date: Wed, 18 Aug 2021 13:46:51 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 8/18/21 3:00 AM, Dr. David Alan Gilbert wrote: > * Jeffle Xu (jefflexu@linux.alibaba.com) wrote: >> For passthrough, when the corresponding virtiofs in guest is mounted >> with '-o dax=inode', advertise that the file is capable of per-file >> DAX if the inode in the backend fs is marked with FS_DAX_FL flag. >> >> Signed-off-by: Jeffle Xu >> --- >> tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ >> 1 file changed, 43 insertions(+) >> >> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c >> index 5b6228210f..4cbd904248 100644 >> --- a/tools/virtiofsd/passthrough_ll.c >> +++ b/tools/virtiofsd/passthrough_ll.c >> @@ -171,6 +171,7 @@ struct lo_data { >> int allow_direct_io; >> int announce_submounts; >> int perfile_dax_cap; /* capability of backend fs */ >> + bool perfile_dax; /* enable per-file DAX or not */ >> bool use_statx; >> struct lo_inode root; >> GHashTable *inodes; /* protected by lo->mutex */ >> @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) >> >> if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { >> conn->want |= FUSE_CAP_PERFILE_DAX; >> + lo->perfile_dax = 1; >> + } >> + else { >> + lo->perfile_dax = 0; >> } >> } >> >> @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, >> return 0; >> } >> >> +/* >> + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be >> + * enabled for this file. >> + */ >> +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, >> + const char *name) >> +{ >> + int res, fd; >> + int ret = false;; >> + unsigned int attr; >> + struct fsxattr xattr; >> + >> + if (!lo->perfile_dax) >> + return false; >> + >> + /* Open file without O_PATH, so that ioctl can be called. */ >> + fd = openat(dir->fd, name, O_NOFOLLOW); >> + if (fd == -1) >> + return false; > > Doesn't that defeat the whole benefit of using O_PATH - i.e. that we > might stumble into a /dev node or something else we're not allowed to > open? As far as I know, virtiofsd will pivot_root/chroot to the source directory, and can only access files inside the source directory specified by "-o source=". Then where do these unexpected files come from? Besides, fd opened without O_PATH here is temporary and used for FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl only. It's closed when the function returns. > >> + if (lo->perfile_dax_cap == DAX_CAP_FLAGS) { >> + res = ioctl(fd, FS_IOC_GETFLAGS, &attr); >> + if (!res && (attr & FS_DAX_FL)) >> + ret = true; >> + } >> + else if (lo->perfile_dax_cap == DAX_CAP_XATTR) { >> + res = ioctl(fd, FS_IOC_FSGETXATTR, &xattr); >> + if (!res && (xattr.fsx_xflags & FS_XFLAG_DAX)) >> + ret = true; >> + } > > This all looks pretty expensive for each lookup. Yes. it can be somehow optimized if we can agree on the way of storing the dax flag persistently. -- Thanks, Jeffle