Re: [dpdk-dev] [PATCH] vfio: correct system call error checking

[Neil Horman <nhorman@tuxdriver.com>]

On Tue, Jun 17, 2014 at 08:21:29PM +0000, Richardson, Bruce wrote:
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Neil Horman
> > Sent: Tuesday, June 17, 2014 12:04 PM
> > To: dev@dpdk.org
> > Subject: [dpdk-dev] [PATCH] vfio: correct system call error checking
> > 
> > Noticed today that ioctl error code return checking was incorrect in some of the
> > vfio code.  ioctl can return a negative value if the system detects an error
> > before the target device/driver can produce a return code.  The dpdk vfio code
> > only checks specfically for the values that it expects, which leaves it open to
> > accepting unexpected error codes as success.  For instance, if the vfio layer
> > noted that the iommu driver hadn't finished registering yet, it would return an
> > -EINVAL error code, but the dpdk would accept that as success, becuase it
> > wasn't
> > 0.
> > 
> > Fix this to specifically check for < 0 error codes
> > 
> > Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> > CC: Thomas Monjalon <thomas.monjalon@6wind.com>
> > ---
> >  lib/librte_eal/linuxapp/eal/eal_pci_vfio.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/lib/librte_eal/linuxapp/eal/eal_pci_vfio.c
> > b/lib/librte_eal/linuxapp/eal/eal_pci_vfio.c
> > index 4de6061..65aa8ad 100644
> > --- a/lib/librte_eal/linuxapp/eal/eal_pci_vfio.c
> > +++ b/lib/librte_eal/linuxapp/eal/eal_pci_vfio.c
> > @@ -319,16 +319,16 @@ pci_vfio_get_container_fd(void)
> > 
> >  		/* check VFIO API version */
> >  		ret = ioctl(vfio_container_fd, VFIO_GET_API_VERSION);
> > -		if (ret != VFIO_API_VERSION) {
> > -			RTE_LOG(ERR, EAL, "  unknown VFIO API version!\n");
> > +		if ((ret < 0) || (ret != VFIO_API_VERSION)) {
> > +			RTE_LOG(ERR, EAL, "  unknown VFIO API version! errno
> > = %d\n", errno);
> >  			close(vfio_container_fd);
> >  			return -1;
> >  		}
> 
> Not sure how this change improves things, since the existing check will already trigger an error on all values <0. Can you please clarify why you think this needs to be changed?
Ah, my bad, the ret < 0 is superfulous, as the != already catches it, but the
log message change is valuable in that it differentiates bad API version
detection from other system errors.  I can respin that if you like.
Neil

> 
> > 
> >  		/* check if we support IOMMU type 1 */
> >  		ret = ioctl(vfio_container_fd, VFIO_CHECK_EXTENSION,
> > VFIO_TYPE1_IOMMU);
> > -		if (!ret) {
> > -			RTE_LOG(ERR, EAL, "  unknown IOMMU driver!\n");
> > +		if (ret <= 0) {
> > +			RTE_LOG(ERR, EAL, "  unknown IOMMU driver! errno =
> > %d\n", errno);
> >  			close(vfio_container_fd);
> >  			return -1;
> >  		}
> 
> Ack on this change part. The previously code was incorrect according to what I read in the docs for VFIO.
> 
> /Bruce
>