Re: [Qemu-block] [Qemu-devel] ping: [PATCH v13] block/raw-posix.c: Make physical devices usable in QEMU under Mac OS X host

[Programmingkid]

On Feb 2, 2016, at 5:04 PM, Eric Blake wrote:

> On 02/02/2016 02:23 PM, Programmingkid wrote:
> 
>>> And why isn't bsd_path usable for that purpose?
>> 
>> After trying it out, I found out why bsd_path isn't usable for that purpose. 
>> It is because the user might try to use a flash drive as the the cdrom. Say 
>> a flash drive is set to /dev/disk2s9. If the user issues the monitor command 
>> "change ide1-cd0 /dev/disk2s9", this will make "if (strcmp(filename, 
>> "/dev/cdrom") == 0)" false and bsd_path would never be set. bsd_path 
>> contents would be garbage.
>> 
>> This would lead to this code not printing the unmounting directions:
>> 
>> if (strncmp(filename, "/dev/", 5) == 0) {
>>           print_unmounting_directions(filename);
>>           return -1;
>>       }
>> 
>> It looks keeping filename as an character array is best.
> 
> No, keep filename as a const char * pointer.  It's easy to avoid use of
> uninitialized memory.  Try this:
> 
> const char *filename;
> char bsd_path[MAXPATHLEN] = "";
> ...
> if (strncmp("/dev/cdrom"...) {
>    bsd_path = ...
> }
> ...
> if (strncmp("/dev/"...) {
>    print_unmounting_directions(*bsd_path ? bsd_path : filename);

At first I thought this code looked unusual, but it does work. Is this ok?

#if defined(__APPLE__) && defined(__MACH__)
        /* if a physical device experienced an error while being opened */
        if (strncmp((*bsd_path ? bsd_path : filename), "/dev/", 5) == 0) {
            print_unmounting_directions(*bsd_path ? bsd_path : filename);
            return -1;
        }
#endif /* defined(__APPLE__) && defined(__MACH__) */