File: username.c

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/*
 *	Top users/processes display for Unix
 *	Version 3
 *
 *	This program may be freely redistributed,
 *	but this entire comment MUST remain intact.
 *
 *	Copyright (c) 1984, 1989, William LeFebvre, Rice University
 *	Copyright (c) 1989, 1990, 1992, William LeFebvre, Northwestern University
 */

/*
 *	Username translation code for top.
 *
 *	These routines handle uid to username mapping.
 *	They use a hashing table scheme to reduce reading overhead.
 *	For the time being, these are very straightforward hashing routines.
 *	Maybe someday I'll put in something better.  But with the advent of
 *	"random access" password files, it might not be worth the effort.
 *
 *	Changes to these have been provided by John Gilmore (gnu@toad.com).
 *
 *	The hash has been simplified in this release, to avoid the
 *	table overflow problems of previous releases.  If the value
 *	at the initial hash location is not right, it is replaced
 *	by the right value.  Collisions will cause us to call getpw*
 *	but hey, this is a cache, not the Library of Congress.
 *	This makes the table size independent of the passwd file size.
 */

#include "os.h"

#include <pwd.h>

#include "pg_top.h"
#include "utils.h"

struct hash_el
{
	int			uid;
	char		name[9];
};

#define    is_empty_hash(x) (hash_table[x].name[0] == 0)

/* simple minded hashing function */
/* Uid "nobody" is -2 results in hashit(-2) = -2 which is out of bounds for
   the hash_table.	Applied abs() function to fix. 2/16/96 tpugh
*/
#define    hashit(i)	(abs(i) % Table_size)

/* K&R requires that statically declared tables be initialized to zero. */
/* We depend on that for hash_table and YOUR compiler had BETTER do it! */
struct hash_el hash_table[Table_size];

void
init_hash()

{
	/*
	 * There used to be some steps we had to take to initialize things. We
	 * don't need to do that anymore, but we will leave this stub in just in
	 * case future changes require initialization steps.
	 */
}

int
enter_user(int uid, char *name, int wecare)

{
	register int hashindex;

#ifdef DEBUG
	dprintf("enter_hash(%d, %s, %d)\n", uid, name, wecare);
#endif

	hashindex = hashit(uid);

	if (!is_empty_hash(hashindex))
	{
		if (!wecare)
			return 0;			/* Don't clobber a slot for trash */
		if (hash_table[hashindex].uid == uid)
			return (hashindex); /* Fortuitous find */
	}

	/* empty or wrong slot -- fill it with new value */
	hash_table[hashindex].uid = uid;
	(void) strncpy(hash_table[hashindex].name, name, 8);
	return (hashindex);
}

/*
 * Get a userid->name mapping from the system.
 * If the passwd database is hashed (#define RANDOM_PW), we
 * just handle this uid.  Otherwise we scan the passwd file
 * and cache any entries we pass over while looking.
 */

int
get_user(int uid)

{
	struct passwd *pwd;

#ifdef RANDOM_PW
	/* no performance penalty for using getpwuid makes it easy */
	if ((pwd = getpwuid(uid)) != NULL)
	{
		return (enter_user(pwd->pw_uid, pwd->pw_name, 1));
	}
#else

	int			from_start = 0;

	/*
	 * If we just called getpwuid each time, things would be very slow since
	 * that just iterates through the passwd file each time.  So, we walk
	 * through the file instead (using getpwent) and cache each entry as we
	 * go.	Once the right record is found, we cache it and return
	 * immediately.  The next time we come in, getpwent will get the next
	 * record.	In theory, we never have to read the passwd file a second time
	 * (because we cache everything we read).  But in practice, the cache may
	 * not be large enough, so if we don't find it the first time we have to
	 * scan the file a second time.  This is not very efficient, but it will
	 * do for now.
	 */

	while (from_start++ < 2)
	{
		while ((pwd = getpwent()) != NULL)
		{
			if (pwd->pw_uid == uid)
			{
				return (enter_user(pwd->pw_uid, pwd->pw_name, 1));
			}
			(void) enter_user(pwd->pw_uid, pwd->pw_name, 0);
		}
		/* try again */
		setpwent();
	}
#endif
	/* if we can't find the name at all, then use the uid as the name */
	return (enter_user(uid, itoa7(uid), 1));
}

char *
username(uid_t uid)

{
	register int hashindex;

	hashindex = hashit(uid);
	if (is_empty_hash(hashindex) || (hash_table[hashindex].uid != uid))
	{
		/* not here or not right -- get it out of passwd */
		hashindex = get_user(uid);
	}
	return (hash_table[hashindex].name);
}

int
userid(char *username)

{
	struct passwd *pwd;

	/*
	 * Eventually we want this to enter everything in the hash table, but for
	 * now we just do it simply and remember just the result.
	 */

	if ((pwd = getpwnam(username)) == NULL)
	{
		return (-1);
	}

	/* enter the result in the hash table */
	enter_user(pwd->pw_uid, username, 1);

	/* return our result */
	return (pwd->pw_uid);
}