On Wed, Jul 24, 2019 at 05:10:24PM -0400, Vivek Goyal wrote:
> 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;
typo? flags is set to O_WRONLY or 0 in do_lookup, although this may work as
same.
thanks,
-liubo
>
> 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);
