username.c revision 24140 
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
12/*
13 *  Username translation code for top.
14 *
15 *  These routines handle uid to username mapping.
16 *  They use a hashing table scheme to reduce reading overhead.
17 *  For the time being, these are very straightforward hashing routines.
18 *  Maybe someday I'll put in something better.  But with the advent of
19 *  "random access" password files, it might not be worth the effort.
20 *
21 *  Changes to these have been provided by John Gilmore (gnu@toad.com).
22 *
23 *  The hash has been simplified in this release, to avoid the
24 *  table overflow problems of previous releases.  If the value
25 *  at the initial hash location is not right, it is replaced
26 *  by the right value.  Collisions will cause us to call getpw*
27 *  but hey, this is a cache, not the Library of Congress.
28 *  This makes the table size independent of the passwd file size.
29 */
30
31#include <stdio.h>
32#include <pwd.h>
33
34#include "top.local.h"
35#include "utils.h"
36
37struct hash_el {
38    int  uid;
39    char name[9];
40};
41
42#define    is_empty_hash(x)	(hash_table[x].name[0] == 0)
43
44/* simple minded hashing function */
45/* Uid "nobody" is -2 results in hashit(-2) = -2 which is out of bounds for
46   the hash_table.  Applied abs() function to fix. 2/16/96 tpugh
47*/
48#define    hashit(i)	(abs(i) % Table_size)
49
50/* K&R requires that statically declared tables be initialized to zero. */
51/* We depend on that for hash_table and YOUR compiler had BETTER do it! */
52struct hash_el hash_table[Table_size];
53
54init_hash()
55
56{
57    /*
58     *  There used to be some steps we had to take to initialize things.
59     *  We don't need to do that anymore, but we will leave this stub in
60     *  just in case future changes require initialization steps.
61     */
62}
63
64char *username(uid)
65
66register int uid;
67
68{
69    register int hashindex;
70
71    hashindex = hashit(uid);
72    if (is_empty_hash(hashindex) || (hash_table[hashindex].uid != uid))
73    {
74	/* not here or not right -- get it out of passwd */
75	hashindex = get_user(uid);
76    }
77    return(hash_table[hashindex].name);
78}
79
80int userid(username)
81
82char *username;
83
84{
85    struct passwd *pwd;
86
87    /* Eventually we want this to enter everything in the hash table,
88       but for now we just do it simply and remember just the result.
89     */
90
91    if ((pwd = getpwnam(username)) == NULL)
92    {
93	return(-1);
94    }
95
96    /* enter the result in the hash table */
97    enter_user(pwd->pw_uid, username, 1);
98
99    /* return our result */
100    return(pwd->pw_uid);
101}
102
103int enter_user(uid, name, wecare)
104
105register int  uid;
106register char *name;
107int wecare;		/* 1 = enter it always, 0 = nice to have */
108
109{
110    register int hashindex;
111
112#ifdef DEBUG
113    fprintf(stderr, "enter_hash(%d, %s, %d)\n", uid, name, wecare);
114#endif
115
116    hashindex = hashit(uid);
117
118    if (!is_empty_hash(hashindex))
119    {
120	if (!wecare)
121	    return 0;		/* Don't clobber a slot for trash */
122	if (hash_table[hashindex].uid == uid)
123	    return(hashindex);	/* Fortuitous find */
124    }
125
126    /* empty or wrong slot -- fill it with new value */
127    hash_table[hashindex].uid = uid;
128    (void) strncpy(hash_table[hashindex].name, name, 8);
129    return(hashindex);
130}
131
132/*
133 * Get a userid->name mapping from the system.
134 * If the passwd database is hashed (#define RANDOM_PW), we
135 * just handle this uid.  Otherwise we scan the passwd file
136 * and cache any entries we pass over while looking.
137 */
138
139int get_user(uid)
140
141register int uid;
142
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, itoa7(uid), 1));
185}
186