As of now we always open file O_RDWR (even if writable mappings are not required). This leads to copy up of file if file is backed by overlayfs and hence nullying advantages of overlayfs.
So open file O_RDONLY if writable mappings are not required. Open O_RDWR if writable mappings are needed. Signed-off-by: Vivek Goyal <[email protected]> --- contrib/virtiofsd/passthrough_ll.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) Index: qemu/contrib/virtiofsd/passthrough_ll.c =================================================================== --- qemu.orig/contrib/virtiofsd/passthrough_ll.c 2019-07-24 16:31:07.014871768 -0400 +++ qemu/contrib/virtiofsd/passthrough_ll.c 2019-07-24 16:32:10.064412722 -0400 @@ -2197,15 +2197,15 @@ static void lo_setupmapping(fuse_req_t r VhostUserFSSlaveMsg msg = { 0 }; uint64_t vhu_flags; char *buf; + bool writable = flags & FUSE_SETUPMAPPING_FLAG_WRITE; if (lo_debug(req)) fuse_debug("lo_setupmapping(ino=%" PRIu64 ", fi=0x%p)\n", ino, (void *)fi); vhu_flags = VHOST_USER_FS_FLAG_MAP_R; - if (flags & O_WRONLY) { + if (writable) vhu_flags |= VHOST_USER_FS_FLAG_MAP_W; - } msg.fd_offset[0] = foffset; msg.len[0] = len; @@ -2223,7 +2223,10 @@ static void lo_setupmapping(fuse_req_t r * TODO: O_RDWR might not be allowed if file is read only or * write only. Fix it. */ - fd = openat(lo->proc_self_fd, buf, O_RDWR); + if (writable) + fd = openat(lo->proc_self_fd, buf, O_RDWR); + else + fd = openat(lo->proc_self_fd, buf, O_RDONLY); free(buf); if (fd == -1) return (void) fuse_reply_err(req, errno);
