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Tue, 29 Sep 2020 17:53:19 -0400 (EDT) Date: Tue, 29 Sep 2020 17:53:19 -0400 From: Vivek Goyal To: "Dr. David Alan Gilbert (git)" Subject: Re: [PULL 26/26] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options Message-ID: <20200929215319.GI220516@redhat.com> References: <20200925120655.295142-1-dgilbert@redhat.com> <20200925120655.295142-27-dgilbert@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200925120655.295142-27-dgilbert@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=vgoyal@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/29 02:22:44 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.687, 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_H5=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: lvivier@redhat.com, quintela@redhat.com, hgcoin@gmail.com, qemu-devel@nongnu.org, peterx@redhat.com, zhengchuan@huawei.com, dovmurik@linux.vnet.ibm.com, zhangjiachen.jaycee@bytedance.com, stefanha@redhat.com, jinyan12@huawei.com, ann.zhuangyanying@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Sep 25, 2020 at 01:06:55PM +0100, Dr. David Alan Gilbert (git) wrote: > From: Jiachen Zhang > > Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, the O_DIRECT > open flag of guest applications will be discarded by virtiofsd. While > this behavior makes it consistent with the virtio-9p scheme when guest > applications use direct I/O, we no longer have any chance to bypass the > host page cache. > > Therefore, we add a flag 'allow_direct_io' to lo_data. If '-o > no_allow_direct_io' option is added, or none of '-o allow_direct_io' or > '-o no_allow_direct_io' is added, the 'allow_direct_io' will be set to > 0, and virtiofsd discards O_DIRECT as before. If '-o allow_direct_io' > is added to the starting command-line, 'allow_direct_io' will be set to > 1, so that the O_DIRECT flags will be retained and host page cache can > be bypassed. Hi Jiachen, Curious that in what cases you want to bypass host page cache. Thanks Vivek > > Signed-off-by: Jiachen Zhang > Reviewed-by: Stefan Hajnoczi > Message-Id: <20200824105957.61265-1-zhangjiachen.jaycee@bytedance.com> > Signed-off-by: Dr. David Alan Gilbert > --- > tools/virtiofsd/helper.c | 4 ++++ > tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------ > 2 files changed, 18 insertions(+), 6 deletions(-) > > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c > index 7bc5d7dc5a..85770d63f1 100644 > --- a/tools/virtiofsd/helper.c > +++ b/tools/virtiofsd/helper.c > @@ -178,6 +178,10 @@ void fuse_cmdline_help(void) > " (0 leaves rlimit unchanged)\n" > " default: min(1000000, fs.file-max - 16384)\n" > " if the current rlimit is lower\n" > + " -o allow_direct_io|no_allow_direct_io\n" > + " retain/discard O_DIRECT flags passed down\n" > + " to virtiofsd from guest applications.\n" > + " default: no_allow_direct_io\n" > ); > } > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 784330e0e4..0b229ebd57 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -151,6 +151,7 @@ struct lo_data { > int timeout_set; > int readdirplus_set; > int readdirplus_clear; > + int allow_direct_io; > struct lo_inode root; > GHashTable *inodes; /* protected by lo->mutex */ > struct lo_map ino_map; /* protected by lo->mutex */ > @@ -179,6 +180,8 @@ static const struct fuse_opt lo_opts[] = { > { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS }, > { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, > { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 }, > + { "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 }, > + { "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 0 }, > FUSE_OPT_END > }; > static bool use_syslog = false; > @@ -1516,7 +1519,8 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t ino, > fuse_reply_err(req, 0); > } > > -static void update_open_flags(int writeback, struct fuse_file_info *fi) > +static void update_open_flags(int writeback, int allow_direct_io, > + struct fuse_file_info *fi) > { > /* > * With writeback cache, kernel may send read requests even > @@ -1541,10 +1545,13 @@ static void update_open_flags(int writeback, struct fuse_file_info *fi) > > /* > * O_DIRECT in guest should not necessarily mean bypassing page > - * cache on host as well. If somebody needs that behavior, it > - * probably should be a configuration knob in daemon. > + * cache on host as well. Therefore, we discard it by default > + * ('-o no_allow_direct_io'). If somebody needs that behavior, > + * the '-o allow_direct_io' option should be set. > */ > - fi->flags &= ~O_DIRECT; > + if (!allow_direct_io) { > + fi->flags &= ~O_DIRECT; > + } > } > > static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, > @@ -1576,7 +1583,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, > goto out; > } > > - update_open_flags(lo->writeback, fi); > + update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW, > mode); > @@ -1786,7 +1793,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi) > fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino, > fi->flags); > > - update_open_flags(lo->writeback, fi); > + update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > sprintf(buf, "%i", lo_fd(req, ino)); > fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); > @@ -2823,6 +2830,7 @@ int main(int argc, char *argv[]) > .debug = 0, > .writeback = 0, > .posix_lock = 0, > + .allow_direct_io = 0, > .proc_self_fd = -1, > }; > struct lo_map_elem *root_elem; > -- > 2.26.2 >