text: /* ISC license. */
  
  #include <string.h>
  #include <stdint.h>
  #include <sys/stat.h>
  #include <sys/sysmacros.h>
  #include <errno.h>
  #include <skalibs/types.h>
  #include <skalibs/allreadwrite.h>
  #include <skalibs/buffer.h>
  #include <skalibs/stralloc.h>
  #include <skalibs/genalloc.h>
  #include <skalibs/djbunix.h>
  #include <skalibs/skamisc.h>
  #include <skalibs/avltree.h>
  #include "s6-ps.h"
  
  static avltree ttycache_tree = AVLTREE_ZERO ;
  static genalloc ttycache_index = GENALLOC_ZERO ;
  
  int s6ps_ttycache_init (void)
  {
    avltree_init(&ttycache_tree, 5, 3, 8, &left_dtok, &uint32_cmp, &ttycache_index) ;
    return 1 ;
  }
  
  void s6ps_ttycache_finish (void)
  {
    avltree_free(&ttycache_tree) ;
    genalloc_free(dius_t, &ttycache_index) ;
  }
  
  static int check (char const *s, dev_t ttynr)
  {
    struct stat st ;
    if (stat(s, &st) < 0) return 0 ;
    return S_ISCHR(st.st_mode) && (st.st_rdev == ttynr) ;
  }
  
  
   /* No blind scanning of all /dev or /sys/devices, kthx */
  
  static int ttyguess (stralloc *sa, dev_t ttynr)
  {
    unsigned int maj = major(ttynr), min = minor(ttynr) ;
  
   /* Try /dev/tty? and /dev/pts/? */
    if (maj == 4 && min < 64)
    {
      char tmp[11] = "/dev/tty" ;
      tmp[uint_fmt(tmp+8, min)] = 0 ;
      if (check(tmp, ttynr)) return stralloc_cats(sa, tmp+5) && stralloc_0(sa) ;
    }
    else if (maj >= 136 && maj < 144)
    {
      unsigned int n = ((maj - 136) << 20) | min ;
      char tmp[9 + UINT_FMT] = "/dev/pts/" ;
      tmp[9 + uint_fmt(tmp+9, n)] = 0 ;
      if (check(tmp, ttynr)) return stralloc_cats(sa, tmp+5) && stralloc_0(sa) ;
    }
  
   /* Use /sys/dev/char/maj:min if it exists */
    {
      int fd ;
      size_t pos = 14 ;
      char path[23 + 2 * UINT_FMT] = "/sys/dev/char/" ;
      pos += uint_fmt(path + pos, maj) ;
      path[pos++] = ':' ;
      pos += uint_fmt(path + pos, min) ;
      memcpy(path + pos, "/uevent", 8) ;
      fd = open_read(path) ;
      if (fd >= 0)
      {
        char buf[4097] ;
        buffer b = BUFFER_INIT(&fd_readv, fd, buf, 4097) ;
        size_t start = satmp.len ;
        int r ;
        for (;;)
        {
          satmp.len = start ;
          r = skagetln(&b, &satmp, '\n') ;
          if (r <= 0) break ;
          if ((satmp.len - start) > 8 && !memcmp(satmp.s + start, "DEVNAME=", 8)) break ;
        }
        fd_close(fd) ;
        if (r > 0)
        {
          satmp.s[satmp.len - 1] = 0 ;
          satmp.len = start ;
          memcpy(satmp.s + start + 3, "/dev/", 5) ;
          if (check(satmp.s + start + 3, ttynr))
            return stralloc_cats(sa, satmp.s + start + 8) && stralloc_0(sa) ;
        }
      }
    }
  
   /* Fallback: print explicit maj:min */
    {
      size_t pos = 1 ;
      char tmp[3 + 2 * UINT_FMT] = "(" ;
      pos += uint_fmt(tmp + pos, maj) ;
      tmp[pos++] = ':' ;
      pos += uint_fmt(tmp + pos, min) ;
      tmp[pos++] = ')' ;
      tmp[pos++] = 0 ;
      return stralloc_catb(sa, tmp, pos) ;
    }
  }
  
  int s6ps_ttycache_lookup (stralloc *sa, dev_t ttynr)
  {
    int wasnull = !satmp.s ;
    dius_t d = { .left = (uint32_t)ttynr, .right = satmp.len } ;
    uint32_t i ;
    if (!avltree_search(&ttycache_tree, &d.left, &i))
    {
      unsigned int n = genalloc_len(dius_t, &ttycache_index) ;
      if (!ttyguess(&satmp, ttynr)) return 0 ;
      if (!genalloc_append(dius_t, &ttycache_index, &d)) goto err ;
      if (!avltree_insert(&ttycache_tree, n))
      {
        genalloc_setlen(dius_t, &ttycache_index, n) ;
        goto err ;
      }
      i = n ;
    }
    return stralloc_cats(sa, satmp.s + genalloc_s(dius_t, &ttycache_index)[i].right) ;
   err:
    {
      int e = errno ;
      if (wasnull) stralloc_free(&satmp) ;
      else satmp.len = d.right ;
      errno = e ;
    }
    return 0 ;
  }
  