Accounting changes

[Diomidis Spinellis]

Rick C. Petty wrote:
> On Fri, Apr 20, 2007 at 12:45:53AM +0300, Diomidis Spinellis wrote:
>> If we follow the route of allowing the records to be read from both 
>> ends, we'll have to think of a construct that will portably maintain 
>> ac_flags at the same offset from the end as in the old struct acct. 
>> Proposals welcomed!
> 
> How about rearranging the struct to have the fixed-sized fields first,
> followed by the variable-sized fields.  In fact I thought that was the
> recommended practice..

The new structure has to provide backwards compatibility with the old 
structure for a program reading a single record either from the 
beginning of a file or from its end (backwards).  This is why ac_flag 
and ac_len2 (which is a copy of ac_len) have to be in the end.

A program reading backwards (e.g. lastcomm(1)) will first read ac_flag. 
  If ANVER is set, it will then read ac_len2, and then the rest of the 
structure.  It will the interpret the structure based on ac_version.  If 
ANVER is not set, the structure is in the old format and the program 
will read the old struct acct.

A program reading forwards will first examine ac_zero.  If it is zero it 
will process the structure based on ac_len and ac_version.  Otherwise 
the structure is in the old format and the program will read the old 
struct acct.

- dds

> i.e.:
> 
>> struct nacct {
>>     u_int8_t      ac_zero;    /* zero identifies new version */
>>     u_int8_t      ac_version; /* record version number */
>>     u_int16_t ac_len;         /* record length */
>>
>>     char      ac_comm[AC_COMM_LEN];    /* command name */
>>     u_int16_t ac_len2;        /* record length */
>>     u_int8_t  ac_flag;        /* accounting flags */
> 
>>     float      ac_utime;      /* user time */
>>     float      ac_stime;      /* system time */
>>     float      ac_etime;      /* elapsed time */
>>     time_t     ac_btime;      /* starting time */
>>     uid_t      ac_uid;        /* user id */
>>     gid_t      ac_gid;        /* group id */
>>     float      ac_mem;        /* average memory usage */
>>     float      ac_io;         /* count of IO blocks */
>>     __dev_t   ac_tty;         /* controlling tty */
> 
> -- Rick C. Petty