Re: [PATCH] tap: fix net_init_tap() return code

[Steven Sistare]

On 4/4/2023 6:00 PM, Philippe Mathieu-Daudé wrote:
> On 4/4/23 18:00, Steve Sistare wrote:
>> When net_init_tap() succeeds for a multi-queue device, it returns a
>> non-zero ret=1 code to its caller, because of this code where ret becomes
> 
> Indeed g_unix_set_fd_nonblocking() returns TRUE on success.
> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> 
>> 1 when g_unix_set_fd_nonblocking succeeds.  Luckily, the only current call
>> site checks for negative, rather than non-zero.
>>
>>      ret = g_unix_set_fd_nonblocking(fd, true, NULL);
>>      if (!ret) {
>>          ...
>>          goto free_fail;
>>
>> Also, if g_unix_set_fd_nonblocking fails (though unlikely), ret=0 is 
>> returned,
>> and the caller will use a broken interface.
> 
> We should return -1 from free_fail, not trying to propagate 'ret':

Thanks for the review.  I will add your "return -1" changes if Jason agrees.

- Steve

> 
> -- >8 --
> diff --git a/net/tap.c b/net/tap.c
> index 1bf085d422..e59238bda0 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -821,3 +821,2 @@ int net_init_tap(const Netdev *netdev, const char *name,
>      char ifname[128];
> -    int ret = 0;
> 
> @@ -896,3 +895,2 @@ int net_init_tap(const Netdev *netdev, const char *name,
>                             "the number of vhostfds passed");
> -                ret = -1;
>                  goto free_fail;
> @@ -904,3 +902,2 @@ int net_init_tap(const Netdev *netdev, const char *name,
>              if (fd == -1) {
> -                ret = -1;
>                  goto free_fail;
> @@ -908,4 +905,3 @@ int net_init_tap(const Netdev *netdev, const char *name,
> 
> -            ret = g_unix_set_fd_nonblocking(fd, true, NULL);
> -            if (!ret) {
> +            if (!g_unix_set_fd_nonblocking(fd, true, NULL)) {
>                  error_setg_errno(errp, errno, "%s: Can't use file descriptor 
> %d",
> @@ -918,3 +914,2 @@ int net_init_tap(const Netdev *netdev, const char *name,
>                  if (vnet_hdr < 0) {
> -                    ret = -1;
>                      goto free_fail;
> @@ -924,3 +919,2 @@ int net_init_tap(const Netdev *netdev, const char *name,
>                             "vnet_hdr not consistent across given tap fds");
> -                ret = -1;
>                  goto free_fail;
> @@ -934,3 +928,2 @@ int net_init_tap(const Netdev *netdev, const char *name,
>                  error_propagate(errp, err);
> -                ret = -1;
>                  goto free_fail;
> @@ -948,3 +941,3 @@ free_fail:
>          g_free(vhost_fds);
> -        return ret;
> +        return -1;
>      } else if (tap->helper) {
> ---
> 
>> Fixes: a8208626ba89.. ("net: replace qemu_set_nonblock()")
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>   net/tap.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)