Re: [Xen-devel] [PATCH for-4.6 1/2] libxl: fix devd removal path

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 23/09/15 a les 10.46, Ian Campbell ha escrit:
> On Tue, 2015-09-22 at 18:23 +0200, Roger Pau Monne wrote:
>>  
>> -    /* Check if event_path ends with "state" and truncate it */
>> -    if (strlen(event_path) < strlen("state"))
>> +    /* Check if event_path ends with "state" or "online" and truncate it. */
>> +    if (strlen(event_path) < strlen("state") ||
>> +        strlen(event_path) < strlen("online"))
> 
> This is the same as strlen(...) < strlen("state") (or more formaly <
> min(strlen("state"),strlen("online")).
> 
> Which is a bit dangerous because one might be tricked into thinking that
> path - strlen("online") was safe to do after this check when it's not. (The
> new code seems to have avoided this particular pattern which the old code
> used though)

With the new code this is no longer needed, so I'm tempted to just
remove it.

> I think I agree with Ian's suggestion to use strrchr.
> 
> Alternatively you could register two watches on the two specific paths you
> care about and point them at wrappers which trivially strip the appropriate
> trailing text and pass the base onto the current code?
> 
> BTW, what is watch_path passed to this function, is it not the watched path
> i.e. the exact truncated event_path that you are looking for?

Watch path is /local/domain/<domid>/backend so we can get an event for
any backend that is added to the domain. We could add specific watches
once we have identified backends that the driver domain needs to serve,
but it's going to make the code more complex and at this point in the
release I don't think that's a good idea.

Roger.


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