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

[Steven Sistare]

On 4/11/2023 2:32 AM, Jason Wang wrote:
> 在 2023/4/5 23:38, Steven Sistare 写道:
>> 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.
> 
> Note that the "free_fail" label is kind of ambiguous. It is used even if we 
> succeed if I was not wrong.

Yes, good catch.  We must return 0 from free_fail on success.
I could delete all uses of ret, test errp in free_fail, and return either -1 or 
0.
Or, you could accept my initial small patch.

What do you prefer?

- 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(-)
>