Message Queue source code in Linux

Linux Message Queue source code-Linux general technology-Linux technology and application information. For more information, see the following section. The source code for sending messages in the message queue in linux. # What kind of behavior should I add alen when applying for a space? How much space is required?
Struct msg_msg * load_msg (const void _ user * src, int len)
{
Struct msg_msg * msg;
Struct msg_msgseg ** using G;
Int err;
Int alen;

Alen = len;
If (alen> DATALEN_MSG)
Alen = DATALEN_MSG;

########## Msg = kmalloc (sizeof (* msg) + alen, GFP_KERNEL );
If (msg = NULL)
Return ERR_PTR (-ENOMEM );

Msg-> next = NULL;
Msg-> security = NULL;

If (copy_from_user (msg + 1, src, alen )){
Err =-EFAULT;
Goto out_err;
}

Len-= alen;
Src = (char _ user *) src) + alen;
Required G = & msg-> next;
While (len> 0 ){
Struct msg_msgseg * seg;
Alen = len;
If (alen> DATALEN_SEG)
Alen = DATALEN_SEG;
Seg = kmalloc (sizeof (* seg) + alen,
GFP_KERNEL );
If (seg = NULL ){
Err =-ENOMEM;
Goto out_err;
}
* Required G = seg;
Seg-> next = NULL;
If (copy_from_user (seg + 1, src, alen )){
Err =-EFAULT;
Goto out_err;
}
Sort G = & seg-> next;
Len-= alen;
Src = (char _ user *) src) + alen;
}

Err = security_msg_msg_alloc (msg );
If (err)
Goto out_err;

Return msg;

Out_err:
Free_msg (msg );
Return ERR_PTR (err );
}