sysctl command with struct

[Pham Viet Ha]

Hi all,

I am writing a code using sysctl to manipulate a kernel variable. The variable is a data structure with two fields, protocol number (uint16_t) and description (char *).

I have some difficulties with sysctl command to pass both protocol number and description at a time to the kernel. I used CTLTYPE_OPAQUE in SYSCTL_ADD_PROC call, then I used sysctl_handle_opaque to read data. 

It does not work correctly. I don't know how what is the format I have to use when I type in "sysctl ..." at the prompt. 

struct protodesc { 
uint16_t protonumber; 
char description[256];
}Add the proc: 

SYSCTL_ADD_PROC(&ctx, SYSCTL_CHILDREN(tree_oidp), OID_AUTO,
    "protodesc", CTLTYPE_OPAQUE | CTLFLAG_RW, 0, 0,
    sysctl_protodesc_update, "S,protodesc",
    "To update protocol and description");

In sysctl_protodesc_update, a call to sysctl_handle_opaque: 

error = sysctl_handle_opaque(oidp, &entry, sizeof entry, req);

entry is of type protodesc. 

Compilation and running both ok. The only issue is that I cannot type in the values for protodesc at sysctl command. I don't know what the format is. 
Error message: sysctl: oid 'protodesc' is type 5, cannot set that. 


Thanks for any help. 

P/S: I sent an incomplete email by accident. Sorry for that. 

HAPVBK