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  * $FreeBSD$
  12  */
  13
  14 /*
  15  *  Username translation code for top.
  16  *
  17  *  These routines handle uid to username mapping.
  18  *  They use a hashing table scheme to reduce reading overhead.
  19  *  For the time being, these are very straightforward hashing routines.
  20  *  Maybe someday I'll put in something better.  But with the advent of
  21  *  "random access" password files, it might not be worth the effort.
  22  *
  23  *  Changes to these have been provided by John Gilmore (gnu@toad.com).
  24  *
  25  *  The hash has been simplified in this release, to avoid the
  26  *  table overflow problems of previous releases.  If the value
  27  *  at the initial hash location is not right, it is replaced
  28  *  by the right value.  Collisions will cause us to call getpw*
  29  *  but hey, this is a cache, not the Library of Congress.
  30  *  This makes the table size independent of the passwd file size.
  31  */
  32
  33 #include <sys/types.h>
  34 #include <stdio.h>
  35 #include <pwd.h>
  36 #include <utmp.h>
  37
  38 #include "top.local.h"
  39 #include "utils.h"
  40
  41 struct hash_el {
  42     int  uid;
  43     char name[UT_NAMESIZE + 1];
  44 };
  45
  46 #define    is_empty_hash(x)     (hash_table[x].name[0] == 0)
  47
  48 /* simple minded hashing function */
  49 /* Uid "nobody" is -2 results in hashit(-2) = -2 which is out of bounds for
  50    the hash_table.  Applied abs() function to fix. 2/16/96 tpugh
  51 */
  52 #define    hashit(i)    (abs(i) % Table_size)
  53
  54 /* K&R requires that statically declared tables be initialized to zero. */
  55 /* We depend on that for hash_table and YOUR compiler had BETTER do it! */
  56 struct hash_el hash_table[Table_size];
  57
  58 init_hash()
  59
  60 {
  61     /*
  62      *  There used to be some steps we had to take to initialize things.
  63      *  We don't need to do that anymore, but we will leave this stub in
  64      *  just in case future changes require initialization steps.
  65      */
  66 }
  67
  68 char *username(uid)
  69
  70 register int uid;
  71
  72 {
  73     register int hashindex;
  74
  75     hashindex = hashit(uid);
  76     if (is_empty_hash(hashindex) || (hash_table[hashindex].uid != uid))
  77     {
  78         /* not here or not right -- get it out of passwd */
  79         hashindex = get_user(uid);
  80     }
  81     return(hash_table[hashindex].name);
  82 }
  83
  84 int userid(username)
  85
  86 char *username;
  87
  88 {
  89     struct passwd *pwd;
  90
  91     /* Eventually we want this to enter everything in the hash table,
  92        but for now we just do it simply and remember just the result.
  93      */
  94
  95     if ((pwd = getpwnam(username)) == NULL)
  96     {
  97         return(-1);
  98     }
  99
 100     /* enter the result in the hash table */
 101     enter_user(pwd->pw_uid, username, 1);
 102
 103     /* return our result */
 104     return(pwd->pw_uid);
 105 }
 106
 107 int enter_user(uid, name, wecare)
 108
 109 register int  uid;
 110 register char *name;
 111 int wecare;             /* 1 = enter it always, 0 = nice to have */
 112
 113 {
 114     register int hashindex;
 115
 116 #ifdef DEBUG
 117     fprintf(stderr, "enter_hash(%d, %s, %d)\n", uid, name, wecare);
 118 #endif
 119
 120     hashindex = hashit(uid);
 121
 122     if (!is_empty_hash(hashindex))
 123     {
 124         if (!wecare)
 125             return 0;           /* Don't clobber a slot for trash */
 126         if (hash_table[hashindex].uid == uid)
 127             return(hashindex);  /* Fortuitous find */
 128     }
 129
 130     /* empty or wrong slot -- fill it with new value */
 131     hash_table[hashindex].uid = uid;
 132     (void) strncpy(hash_table[hashindex].name, name, UT_NAMESIZE);
 133     return(hashindex);
 134 }
 135
 136 /*
 137  * Get a userid->name mapping from the system.
 138  * If the passwd database is hashed (#define RANDOM_PW), we
 139  * just handle this uid.  Otherwise we scan the passwd file
 140  * and cache any entries we pass over while looking.
 141  */
 142
 143 int get_user(uid)
 144
 145 register int uid;
 146
 147 {
 148     struct passwd *pwd;
 149
 150 #ifdef RANDOM_PW
 151     /* no performance penalty for using getpwuid makes it easy */
 152     if ((pwd = getpwuid(uid)) != NULL)
 153     {
 154         return(enter_user(pwd->pw_uid, pwd->pw_name, 1));
 155     }
 156 #else
 157
 158     int from_start = 0;
 159
 160     /*
 161      *  If we just called getpwuid each time, things would be very slow
 162      *  since that just iterates through the passwd file each time.  So,
 163      *  we walk through the file instead (using getpwent) and cache each
 164      *  entry as we go.  Once the right record is found, we cache it and
 165      *  return immediately.  The next time we come in, getpwent will get
 166      *  the next record.  In theory, we never have to read the passwd file
 167      *  a second time (because we cache everything we read).  But in
 168      *  practice, the cache may not be large enough, so if we don't find
 169      *  it the first time we have to scan the file a second time.  This
 170      *  is not very efficient, but it will do for now.
 171      */
 172
 173     while (from_start++ < 2)
 174     {
 175         while ((pwd = getpwent()) != NULL)
 176         {
 177             if (pwd->pw_uid == uid)
 178             {
 179                 return(enter_user(pwd->pw_uid, pwd->pw_name, 1));
 180             }
 181             (void) enter_user(pwd->pw_uid, pwd->pw_name, 0);
 182         }
 183         /* try again */
 184         setpwent();
 185     }
 186 #endif
 187     /* if we can't find the name at all, then use the uid as the name */
 188     return(enter_user(uid, itoa7(uid), 1));
 189 }