shmget() returns xx if current user is not a administrator

patrick ficheux pficheux@prologue.fr
Fri Oct 12 09:45:00 GMT 2007


Corinna Vinschen a écrit :
> On Oct 12 11:09, patrick ficheux wrote:
>   
>> In SANE (scanner project), the backend for snapscan failed to call shmget() 
>> with error EACCES (Permission denied) if the current user isn't 
>> administrator.
>> When I'am logged as windows administrator, shmget() is called successfully
>>
>> In both case, the env. variable CYGWIN exists and this value is 
>> CYGWIN=server
>> cygserver is installed and runs
>>
>>
>> Is it possible to call shmget() without administrator's privileges ?
>> In this case, what kind of privileges a user must have ? and how to set 
>> those privileges ?
>>
>> Thanks
>>
>> extract from snapscan backend
>>
>> #ifndef SHM_R
>> #define SHM_R 0
>> #endif
>>
>> #ifndef SHM_W
>> #define SHM_W 0
>> #endif
>>     
>
> ^^^^^^^^^^^^^^^^^^^^
> This is the problem.  SHM_R and SHM_W are not defined on Cygwin.
> These flags are not defined by POSIX and relying on them as above is
> non-portable.  As a result, you create a shared mem region with
> permission bits set to 000.
>
>   
>>    int shm_id = shmget (IPC_PRIVATE, shm_size, IPC_CREAT | SHM_R | SHM_W);
>>     
>
> Try something like
>
>      #include <sys/stat.h>
>      int shm_id = shmget (IPC_PRIVATE, shm_size, IPC_CREAT | S_IRWXU);
>   
it works fine !
thanks a lot



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