contrib/top/username.c

   1 /*
   2  *  Top users/processes display for Unix
   3  *  Version 3
   4  *
   5  *  This program may be freely redistributed,
   6  *  but this entire comment MUST remain intact.
   7  *
   8  *  Copyright (c) 1984, 1989, William LeFebvre, Rice University
   9  *  Copyright (c) 1989, 1990, 1992, William LeFebvre, Northwestern University
  10  *
  11  * $FreeBSD: src/contrib/top/username.c,v 1.2.8.1 2002/08/11 17:09:25 dwmalone Exp $
  12  * $DragonFly: src/contrib/top/username.c,v 1.2 2003/06/17 04:24:07 dillon Exp $
  13  */
  14
  15 /*
  16  *  Username translation code for top.
  17  *
  18  *  These routines handle uid to username mapping.
  19  *  They use a hashing table scheme to reduce reading overhead.
  20  *  For the time being, these are very straightforward hashing routines.
  21  *  Maybe someday I'll put in something better.  But with the advent of
  22  *  "random access" password files, it might not be worth the effort.
  23  *
  24  *  Changes to these have been provided by John Gilmore (gnu@toad.com).
  25  *
  26  *  The hash has been simplified in this release, to avoid the
  27  *  table overflow problems of previous releases.  If the value
  28  *  at the initial hash location is not right, it is replaced
  29  *  by the right value.  Collisions will cause us to call getpw*
  30  *  but hey, this is a cache, not the Library of Congress.
  31  *  This makes the table size independent of the passwd file size.
  32  */
  33
  34 #include <sys/types.h>
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <pwd.h>
  39 #include <utmp.h>
  40
  41 #include "top.local.h"
  42 #include "utils.h"
  43 #include "username.h"
  44
  45 struct hash_el {
  46     int  uid;
  47     char name[UT_NAMESIZE + 1];
  48 };
  49
  50 static int get_user(int uid);
  51
  52 #define    is_empty_hash(x)     (hash_table[x].name[0] == 0)
  53
  54 /* simple minded hashing function */
  55 /* Uid "nobody" is -2 results in hashit(-2) = -2 which is out of bounds for
  56    the hash_table.  Applied abs() function to fix. 2/16/96 tpugh
  57 */
  58 #define    hashit(i)    (abs(i) % Table_size)
  59
  60 /* K&R requires that statically declared tables be initialized to zero. */
  61 /* We depend on that for hash_table and YOUR compiler had BETTER do it! */
  62 struct hash_el hash_table[Table_size];
  63
  64 void
  65 init_hash(void)
  66 {
  67     /*
  68      *  There used to be some steps we had to take to initialize things.
  69      *  We don't need to do that anymore, but we will leave this stub in
  70      *  just in case future changes require initialization steps.
  71      */
  72 }
  73
  74 char *
  75 username(long uid)
  76 {
  77     int hashindex;
  78
  79     hashindex = hashit(uid);
  80     if (is_empty_hash(hashindex) || (hash_table[hashindex].uid != uid))
  81     {
  82         /* not here or not right -- get it out of passwd */
  83         hashindex = get_user(uid);
  84     }
  85     return(hash_table[hashindex].name);
  86 }
  87
  88 int
  89 userid(char *xusername)
  90 {
  91     struct passwd *pwd;
  92
  93     /* Eventually we want this to enter everything in the hash table,
  94        but for now we just do it simply and remember just the result.
  95      */
  96
  97     if ((pwd = getpwnam(xusername)) == NULL)
  98     {
  99         return(-1);
 100     }
 101
 102     /* enter the result in the hash table */
 103     enter_user(pwd->pw_uid, xusername, 1);
 104
 105     /* return our result */
 106     return(pwd->pw_uid);
 107 }
 108
 109 int
 110 enter_user(int uid, char *name, int wecare)
 111 {
 112     int hashindex;
 113
 114 #ifdef DEBUG
 115     fprintf(stderr, "enter_hash(%d, %s, %d)\n", uid, name, wecare);
 116 #endif
 117
 118     hashindex = hashit(uid);
 119
 120     if (!is_empty_hash(hashindex))
 121     {
 122         if (!wecare)
 123             return 0;           /* Don't clobber a slot for trash */
 124         if (hash_table[hashindex].uid == uid)
 125             return(hashindex);  /* Fortuitous find */
 126     }
 127
 128     /* empty or wrong slot -- fill it with new value */
 129     hash_table[hashindex].uid = uid;
 130     (void) strncpy(hash_table[hashindex].name, name, UT_NAMESIZE);
 131     return(hashindex);
 132 }
 133
 134 /*
 135  * Get a userid->name mapping from the system.
 136  * If the passwd database is hashed (#define RANDOM_PW), we
 137  * just handle this uid.  Otherwise we scan the passwd file
 138  * and cache any entries we pass over while looking.
 139  */
 140
 141 static int
 142 get_user(int uid)
 143 {
 144     struct passwd *pwd;
 145
 146 #ifdef RANDOM_PW
 147     /* no performance penalty for using getpwuid makes it easy */
 148     if ((pwd = getpwuid(uid)) != NULL)
 149     {
 150         return(enter_user(pwd->pw_uid, pwd->pw_name, 1));
 151     }
 152 #else
 153
 154     int from_start = 0;
 155
 156     /*
 157      *  If we just called getpwuid each time, things would be very slow
 158      *  since that just iterates through the passwd file each time.  So,
 159      *  we walk through the file instead (using getpwent) and cache each
 160      *  entry as we go.  Once the right record is found, we cache it and
 161      *  return immediately.  The next time we come in, getpwent will get
 162      *  the next record.  In theory, we never have to read the passwd file
 163      *  a second time (because we cache everything we read).  But in
 164      *  practice, the cache may not be large enough, so if we don't find
 165      *  it the first time we have to scan the file a second time.  This
 166      *  is not very efficient, but it will do for now.
 167      */
 168
 169     while (from_start++ < 2)
 170     {
 171         while ((pwd = getpwent()) != NULL)
 172         {
 173             if (pwd->pw_uid == uid)
 174             {
 175                 return(enter_user(pwd->pw_uid, pwd->pw_name, 1));
 176             }
 177             (void) enter_user(pwd->pw_uid, pwd->pw_name, 0);
 178         }
 179         /* try again */
 180         setpwent();
 181     }
 182 #endif
 183     /* if we can't find the name at all, then use the uid as the name */
 184     return(enter_user(uid, ltoa7(uid), 1));
 185 }