[fpc-pascal] Linux IPC (SHM) : Getting Strange Value for shm_nattch (# of attachements)

[Tom__G]

Henry Vermaak wrote:
> 
> 2009/10/13 Tom__G <tom at guilleminot.org>:
>>
>> Hi,
>>
>> I try to get number of processes attached to a specific shared memory
>> segment.
>> So I read the shmctl record to retrieve this into shared memory :
>>
>> type TShmid_ds = record
>>  shm_perm: TIPC_Perm; Permissions
>>  shm_segsz: cint; Segment size
>>  shm_atime: time_t; Last access time
>>  shm_dtime: time_t; Last detach time
>>  shm_ctime: time_t; Create time
>>  shm_cpid: ipc_pid_t; Creator PID
>>  shm_lpid: ipc_pid_t; Last operation PID
>>  shm_nattch: Word; Number of attachments  <--<< !
>>  shm_npages: Word; Number of pages
>>  shm_pages: Pointer; ?
>>  attaches: pointer; ?
>> end;
> 
> This definition differs from the one I've got in
> /usr/include/bits/shm.h, where shm_nattch is defined as "unsigned long
> int", so you may want to look into that.  I haven't tried this myself,
> so sorry if I'm barking up the wrong tree...
> 
> Henry
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-pascal
> 
> 



Thanks for suggestion. You may actually talk about this mismatch :
    
    C  : unsigned long int	(4 bytes) :	0 to 4 294 967 295
    FP : word                         : integers from 0 to 65535 


Into my /usr/share/fpcsrc/2.2.4/rtl/unix/ipc.pp I found :

{ ----------------------------------------------------------------------
  Sys V Shared memory stuff
  ----------------------------------------------------------------------}

Type
  PShmid_DS = ^TShmid_ds;
{$ifdef linux}
{$ifdef cpux86_64}
  TShmid_ds = record
    shm_perm  : TIPC_Perm;
    shm_segsz : size_t;
    shm_atime : time_t;
    shm_dtime : time_t;
    shm_ctime : time_t;
    shm_cpid  : pid_t;
    shm_lpid  : pid_t;
    shm_nattch : culong;        <--<<
    __unused4 : culong;
    __unused5 : culong;
  end;
{$else cpux86_64}
  TShmid_ds = record
    shm_perm  : TIPC_Perm;
    shm_segsz : cint;
    shm_atime : time_t;
    shm_dtime : time_t;
    shm_ctime : time_t;
    shm_cpid  : ipc_pid_t;
    shm_lpid  : ipc_pid_t;
    shm_nattch : word;        <--<<
    shm_npages : word;
    shm_pages  : Pointer;
    attaches   : pointer;
  end;
{$endif cpux86_64}
{$else} // FreeBSD checked
  TShmid_ds = record
    shm_perm  : TIPC_Perm;
    shm_segsz : cint;
    shm_lpid  : pid_t;
    shm_cpid  : pid_t;
    shm_nattch : cshort;        <--<<
    shm_atime : time_t;
    shm_dtime : time_t;
    shm_ctime : time_t;
    shm_internal : pointer;
  end;
{$endif}

My hardware here is x86 (not x86_64).
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