Date: Fri, 12 Oct 2007 11:30:46 +0200
From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: shmget() returns xx if current user is not a administrator
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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);

instead.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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