From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 20 Aug 2019 14:37:46 -0400 From: Vivek Goyal Message-ID: <20190820183746.GF4233@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [Virtio-fs] [PATCH V2] virtiofsd: Reset O_DIRECT flag during file open List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: virtio-fs-list , "Dr. David Alan Gilbert" If an application wants to do direct IO and opens a file with O_DIRECT in guest, that does not necessarily mean that we need to bypass page cache on host as well. So reset this flag on host. If somebody needs to bypass page cache on host as well (and it is safe to do so), we can add a knob in daemon later to control this behavior. I check virtio-9p and they do reset O_DIRECT flag. Signed-off-by: Vivek Goyal --- contrib/virtiofsd/passthrough_ll.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) Index: qemu/contrib/virtiofsd/passthrough_ll.c =================================================================== --- qemu.orig/contrib/virtiofsd/passthrough_ll.c 2019-08-20 09:33:07.900975145 -0400 +++ qemu/contrib/virtiofsd/passthrough_ll.c 2019-08-20 14:31:39.725781357 -0400 @@ -1752,6 +1752,13 @@ static void lo_create(fuse_req_t req, fu if (err) goto out; + /* + * 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. + */ + fi->flags &= ~O_DIRECT; + fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW, mode); err = fd == -1 ? errno : 0; @@ -1967,6 +1974,13 @@ static void lo_open(fuse_req_t req, fuse if (lo->writeback && (fi->flags & O_APPEND)) fi->flags &= ~O_APPEND; + /* + * 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. + */ + fi->flags &= ~O_DIRECT; + sprintf(buf, "%i", lo_fd(req, ino)); fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); if (fd == -1)