Re: [Qemu-devel] [PATCH 4/4] ivshmem: check the value returned by fstat()

[zhanghailiang]

Hi Michael,
Thanks for your review of this patch!

> On Mon, Aug 04, 2014 at 04:25:44PM +0800, zhanghailiang wrote:
> > The function fstat() may fail, so check its return value.
> >
> > Signed-off-by: zhanghailiang<address@hidden>
> > ---
> >   hw/misc/ivshmem.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> > index 768e528..2667e9f 100644
> > --- a/hw/misc/ivshmem.c
> > +++ b/hw/misc/ivshmem.c
> > @@ -324,7 +324,10 @@ static int check_shm_size(IVShmemState *s, int fd) {
> >
> >       struct stat buf;
> >
> > -    fstat(fd,&buf);
> > +    if (fstat(fd,&buf)<  0) {
> > +        fprintf(stderr, "Cannot stat IVSHMEM: %s\n", strerror(errno));
> > +        return -1;
> > +    }
>
> That's a confusing error message:
> 1. You don't stat ivshmem. You stat a shmem fd. Also best to print fd #.
I will add this in next version of the patch.
> 2. Tell the user what action was taken, e.g. IVSHMEM failed to start.
>
> >       if (s->ivshmem_size>  buf.st_size) {
> >           fprintf(stderr,
> > --
I have check the places of calling this function, And found that, if 
this function return -1, qemu will call exit(-1). One of the callers is 
ivshmem_read(), the purpose of check_shm_size() is to forbid guest to 
map more memory than the object has allocated. So here is it suitable to 
return -1 if fstat() failed? Or just give a warning message and return 0?
what's your opinion? Thanks.
> > 1.7.12.4
>
> .

Best regards,
zhanghailiang