Re: [Xen-devel] [PATCH v3 07/11] igd: revamp host config read

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 5 Jan 2016, Gerd Hoffmann wrote:
> Move all work to the host_pci_config_copy helper function,
> which we can easily reuse when adding q35 support.
> Open sysfs file only once for all values.  Use pread.
> Proper error handling.  Fix bugs:
> 
>  * Don't throw away results (like old host_pci_config_read
>    did because val was passed by value not reference).
>  * Update config space directly (writing via
>    pci_default_write_config only works for registers
>    whitelisted in wmask).
> 
> Hmm, this code can hardly ever worked before,
> /me wonders what test coverage it had.
> 
> With this patch in place igd-passthru=on actually
> works, although it still requires root priviledges
> because linux refuses to allow non-root users access
> pci config space above offset 0x50.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> ---
>  hw/pci-host/igd.c | 65 
> +++++++++++++++++++++++--------------------------------
>  1 file changed, 27 insertions(+), 38 deletions(-)
> 
> diff --git a/hw/pci-host/igd.c b/hw/pci-host/igd.c
> index 0784128..ec48875 100644
> --- a/hw/pci-host/igd.c
> +++ b/hw/pci-host/igd.c
> @@ -19,47 +19,39 @@ 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_copy(PCIDevice *guest, const char *host,
> +                                 const IGDHostInfo *list, int len, Error 
> **errp)
>  {
> -    char path[PATH_MAX];
> -    int config_fd;
> -    ssize_t size = sizeof(path);
> -    /* 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;
> +    char *path;
> +    int config_fd, rc, i;
>  
> -    if (rc >= size || rc < 0) {
> -        return -ENODEV;
> -    }
> -
> -    config_fd = open(path, O_RDWR);
> +    path = g_strdup_printf("/sys/bus/pci/devices/%s/config", host);
> +    config_fd = open(path, O_RDONLY);
>      if (config_fd < 0) {
> -        return -ENODEV;
> +        error_setg_file_open(errp, errno, path);
> +        goto out_free;
>      }
>  
> -    if (lseek(config_fd, pos, SEEK_SET) != pos) {
> -        ret = -errno;
> -        goto out;
> +    for (i = 0; i < len; i++) {
> +        rc = pread(config_fd, guest->config + list[i].offset,
> +                   list[i].len, list[i].offset);
> +        if (rc != list[i].len) {

pread is allowed to return early, returning the number of bytes read.



> +            error_setg_errno(errp, errno, "read %s, offset 0x%x",
> +                             path, list[i].offset);
> +            goto out_close;
> +        }
>      }
> -    do {
> -        rc = read(config_fd, (uint8_t *)&val, len);
> -    } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
> -    if (rc != len) {
> -        ret = -errno;
> -    }
> -out:
> +
> +out_close:
>      close(config_fd);
> -    return ret;
> +out_free:
> +    g_free(path);
>  }
>  
>  static void (*i440fx_realize)(PCIDevice *pci_dev, Error **errp);
>  static void igd_pt_i440fx_realize(PCIDevice *pci_dev, Error **errp)
>  {
>      Error *err = NULL;
> -    uint32_t val = 0;
> -    int rc, i, num;
> -    int pos, len;
>  
>      i440fx_realize(pci_dev, &err);
>      if (err != NULL) {
> @@ -67,16 +59,13 @@ static void igd_pt_i440fx_realize(PCIDevice *pci_dev, 
> Error **errp)
>          return;
>      }
>  
> -    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) {
> -            error_setg(errp, "failed to read host config");
> -            return;
> -        }
> -        pci_default_write_config(pci_dev, pos, val, len);
> +    host_pci_config_copy(pci_dev, "0000:00:00.0",
> +                         igd_host_bridge_infos,
> +                         ARRAY_SIZE(igd_host_bridge_infos),
> +                         &err);
> +    if (err != NULL) {
> +        error_propagate(errp, err);
> +        return;
>      }
>  }
>  
> -- 
> 1.8.3.1
> 

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