Re: [Qemu-devel] [PATCH v4] igd-passthrough-i440FX: convert to realize()

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Dec 29, 2015 at 04:46:03PM +0800, Cao jin wrote:
> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
> ---
> changelog v4:
> 1. strip the bugfix code, but I guess this patch should be applied after
>    that bugfix patch.
> 2. Other little fix as per previous review
> 
> Some explanation to previous review:
> 1. error_setg_errno() I use in this patch will print the strerror(errno), so I
>    guess it will be informative enough? example:
> 
>    error_setg_errno(errp, errno, "open %s fail", path); will print:
>    "open bluhbluh fail: string_from_strerrer(errno)"

I'd prefer some mention of why this is attempted too.
E.g. "igd passthrough : open bluhbluh fail"

> 2. snprintf() has tiny tiny chance to fail,

It just formats a string into a buffer. the buffer
is pre-allocated, and we know it's large enough for the data.
How can it fail?


> I don`t assert here, because this
>    device is on-board, it init during machine initialization, in case it fails,
>    the errp we set will results in error_report(err) and exit(1), at least can
>    let user know why fail. see the call-chain:
> 
>    pc_xen_hvm_init_pci->pc_init1->i440fx_init->pci_create_simple-> pci_create_simple_multifunction->qdev_init_nofail

unlike open failing, there's nothing user can do, this means there's
a coding bug somewhere, and assert is easier to debug.

> About test:
> 1. Compiled
> 2. Did a dirty hack to force create/realize this device in pc_init1(), prove
>    that the realizing process is ok, I will reply this mail later to attch the
>    screenshot evidence

Good job, thanks!
You should also Cc Tiejun Chen <tiejun.chen@intel.com> who wrote this
code, presumably with access to hardware to test on.


>  hw/pci-host/piix.c | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
> index a9cb983..e91570f 100644
> --- a/hw/pci-host/piix.c
> +++ b/hw/pci-host/piix.c
> @@ -761,7 +761,7 @@ static const IGDHostInfo igd_host_bridge_infos[] = {
>      {0xa8, 4},  /* SNB: base of GTT stolen memory */
>  };
>  
> -static int host_pci_config_read(int pos, int len, uint32_t *val)
> +static void host_pci_config_read(int pos, int len, uint32_t *val, Error **errp)
>  {
>      char path[PATH_MAX];
>      int config_fd;
> @@ -769,19 +769,19 @@ static int host_pci_config_read(int pos, int len, uint32_t *val)
>      /* Access real host bridge. */
>      int rc = snprintf(path, size, "/sys/bus/pci/devices/%04x:%02x:%02x.%d/%s",
>                        0, 0, 0, 0, "config");
> -    int ret = 0;
>  
>      if (rc >= size || rc < 0) {
> -        return -ENODEV;
> +        error_setg_errno(errp, errno, "snprintf err");
>      }
>  
>      config_fd = open(path, O_RDWR);
>      if (config_fd < 0) {
> -        return -ENODEV;
> +        error_setg_errno(errp, errno, "open %s fail", path);
> +        return;
>      }
>  
>      if (lseek(config_fd, pos, SEEK_SET) != pos) {
> -        ret = -errno;
> +        error_setg_errno(errp, errno, "lseek err");
>          goto out;
>      }
>  
> @@ -789,32 +789,32 @@ static int host_pci_config_read(int pos, int len, uint32_t *val)
>          rc = read(config_fd, (uint8_t *)val, len);
>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>      if (rc != len) {
> -        ret = -errno;
> +        error_setg_errno(errp, errno, "read err");
>      }
>  
>  out:
>      close(config_fd);
> -    return ret;
>  }
>  
> -static int igd_pt_i440fx_initfn(struct PCIDevice *pci_dev)
> +static void igd_pt_i440fx_realize(struct PCIDevice *pci_dev, Error **errp)
>  {
>      uint32_t val = 0;
> -    int rc, i, num;
> +    int i, num;
>      int pos, len;
> +    Error *local_err = NULL;
>  
>      num = ARRAY_SIZE(igd_host_bridge_infos);
>      for (i = 0; i < num; i++) {
>          pos = igd_host_bridge_infos[i].offset;
>          len = igd_host_bridge_infos[i].len;
> -        rc = host_pci_config_read(pos, len, &val);
> -        if (rc) {
> -            return -ENODEV;
> +
> +        host_pci_config_read(pos, len, &val, &local_err);
> +        if (local_err) {
> +            error_propagate(errp, local_err);
> +            return;
>          }
>          pci_default_write_config(pci_dev, pos, cpu_to_le32(val), len);
>      }
> -
> -    return 0;
>  }
>  
>  static void igd_passthrough_i440fx_class_init(ObjectClass *klass, void *data)
> @@ -822,7 +822,7 @@ static void igd_passthrough_i440fx_class_init(ObjectClass *klass, void *data)
>      DeviceClass *dc = DEVICE_CLASS(klass);
>      PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
>  
> -    k->init = igd_pt_i440fx_initfn;
> +    k->realize = igd_pt_i440fx_realize;
>      dc->desc = "IGD Passthrough Host bridge";
>  }
>  
> -- 
> 2.1.0
> 
>