username.c revision 200979 
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: head/contrib/top/username.c 200979 2009-12-25 09:02:41Z ed $
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/param.h>
34#include <sys/types.h>
35#include <stdio.h>
36#include <pwd.h>
37
38#include "top.local.h"
39#include "utils.h"
40
41struct hash_el {
42    int  uid;
43    char name[MAXLOGNAME];
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! */
56struct hash_el hash_table[Table_size];
57
58init_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
68char *username(uid)
69
70register 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
84int userid(username)
85
86char *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
107int enter_user(uid, name, wecare)
108
109register int  uid;
110register char *name;
111int 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, MAXLOGNAME - 1);
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
143int get_user(uid)
144
145register 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}
190