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

[Michael S. Tsirkin]

On Tue, Aug 05, 2014 at 10:00:41AM +0800, zhanghailiang wrote:
> 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.

So put "exiting" In the error message then.

> >>1.7.12.4
> >>
> >
> >.
> >
> 
> Best regards,
> zhanghailiang