* Liu Bo ([email protected]) wrote:
> 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.
Right; that should be O_WRONLY;
do_setupmapping does:
genflags = 0;
genflags |= (arg->flags & FUSE_SETUPMAPPING_FLAG_WRITE) ? O_WRONLY : 0;
to convert from the fuse definition on the wire to the O_ notation
before calling the filesstem code.
Dave
> 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);
--
Dr. David Alan Gilbert / [email protected] / Manchester, UK
