Re: utmpx support

[finkler <finkler@officinamentis.org>]

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On 04.03.2012 19:18, Rich Felker wrote:
> On Sun, Mar 04, 2012 at 06:41:25PM +0100, finkler wrote:
>
> It's intentional, but if you have a real need for utmp support, I'd be
> willing to hear about it.

Well, I am currently trying to implement new (POSIX) user-space 
utilities for Linux, including my own init/login system.
I thought quite a bit about the purpose of utmp(x) myself I admit, 
however, I came to the conclusion that even though I know no one who 
still uses serial terminals to connect to a machine, connecting through 
LAN/Internet is very popular, and it couldn't hurt that an administrator 
has the means to easily see who is currently logged in (who).

I agree that utmpx has grown disproportionally and has lots of misuses 
which just bloat the code.
But as I said, some method of accessing login information seems sane to 
me. And if used with restrain utmpx is quite well suited for this ... I 
think.

> Perhaps a better approach would be making a separate small static
> libutmp.a that could be linked by people wanting real utmp support as
> opposed to the stubs.

Certainly, for what it's worth, I hacked up an utmpx implementation.
I hope I didn't make any mistakes (code and standard wise), but the code 
size is small, so it should be easily verifiable for another set of eyes 
:-).

Regards, and thank you very much for the good work with this lib, it is 
really great.

Finkler


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#include <utmpx.h>
#include <stddef.h>
#include "libc.h"

#define _PATH_UTMPX "/etc/utmp"

static FILE *f;
static struct utmpx ut;

void endutxent(void)
{
  memset(&ut, 0, sizeof ut);
  if (f == NULL) return;
  fclose(f);
  f == NULL;
}

void setutxent(void)
{
  memset(&ut, 0, sizeof ut);
  if (f == NULL) return;
  rewind(f);
}

struct utmpx *getutxent(void)
{
	if (f == NULL) {
    f = fopen(_PATH_UTMPX, "a+");
    if (f == NULL) {
      f = fopen(_PATH_UTMPX, "r");
      if (f == NULL) return NULL;
    }
  }
  if (fread(&ut, sizeof ut, 1, f)) return &ut;
  return NULL;
}

struct utmpx *getutxid(const struct utmpx *id)
{  
  while(getutxent()) {
    switch (id->ut_type) {
      case BOOT_TIME:
      case OLD_TIME:
      case NEW_TIME:
        if (id->ut_type == ut.ut_type) return &ut;
        break;
      case INIT_PROCESS:
      case LOGIN_PROCESS:
      case USER_PROCESS:
      case DEAD_PROCESS:
        if (id->type == ut.ut_type && !strcmp(id->ut_id, ut.ut_id)) return &ut;
        break;
    }
  }    
  return NULL;
}

struct utmpx *getutxline(const struct utmpx *line)
{
	while(getutxent()) {
    switch (ut.ut_type) {
      case LOGIN_PROCESS:
      case USER_PROCESS:
        if (!strcmp(line->ut_line, ut.ut_line)) return &ut;
        break;
    }
  }
  return NULL;
}

struct utmpx *pututxline(const struct utmpx *utmpx)
{
  setutxent();
  if (getutxid(utmpx)) fseek(f, -(sizeof ut), SEEK_CUR);
  if (fwrite(&ut, sizeof ut, 1, f)) return &ut;
  return NULL;
}

void updwtmpx(const char *f, const struct utmpx *u)
{
}

weak_alias(endutxent, endutent);
weak_alias(setutxent, setutent);
weak_alias(getutxent, getutent);
weak_alias(getutxid, getutid);
weak_alias(getutxline, getutline);
weak_alias(pututxline, pututline);
weak_alias(updwtmpx, updwtmp);