Re: [Xen-devel] [PATCH RFC 03/14] libxc: Fix xc_domain_get_tsc_info returning -Exx instead of -1.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-03-16 at 10:11 -0400, Konrad Rzeszutek Wilk wrote:
>  static void hypercall_buffer_cache_lock(xc_interface *xch)
>  {
> +    int saved_errno;
>      if ( xch->flags & XC_OPENFLAG_NON_REENTRANT )
>          return;
> +    saved_errno = errno;

You can do the init on declaration.

> diff --git a/tools/libxc/xc_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
> index a19e4b6..15d772b 100644
> --- a/tools/libxc/xc_linux_osdep.c
> +++ b/tools/libxc/xc_linux_osdep.c
> @@ -122,10 +122,13 @@ out:
>  
>  static void linux_privcmd_free_hypercall_buffer(xc_interface *xch, 
> xc_osdep_handle h, void *ptr, int npages)
>  {
> +    int saved_errno = errno;
>      /* Recover the VMA flags. Maybe it's not necessary */
>      madvise(ptr, npages * XC_PAGE_SIZE, MADV_DOFORK);
>  
>      munmap(ptr, npages * XC_PAGE_SIZE);
> +    /* We MUST propagate the hypercall errno, not unmap calls. */

Hrm, in general you would want to propagate failure here if the mmap had
succeeded, otherwise you want the mmap failure. Which would involve
pushing the saving into the callers.

But since this function is (for better or worse) void (mainly because it
may trigger out of band due to the cache) I think you are right to
preserve the errno as you've done.

> +    errno = saved_errno;
>  }
>  
>  static int linux_privcmd_hypercall(xc_interface *xch, xc_osdep_handle h, 
> privcmd_hypercall_t *hypercall)
> > 
> > 
> > Ian.
> > 



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