lslogins: consolidate and optimize utmp files use

* the original read_utmp() code is from GPLv3+, but lslogins is GPLv2+
  (see https://github.com/karelzak/util-linux/commit/a6bf40ee77a85f5108208dc764b5d023a07998f5#commitcomment-53407151)

* remove redundant parse_btmp() and parse_wtmp() as it does not
  provide anything

* reduce realloc() calls, allocate all in one step

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/login-utils/lslogins.c b/login-utils/lslogins.c
index d5e9638bfb777674661d0224b82f58352fad6b3f..908d78b11a322fa0f88e21c9e187c6a3810f5b74 100644 (file)
--- a/login-utils/lslogins.c
+++ b/login-utils/lslogins.c
@@ -474,55 +474,52 @@ static struct utmpx *get_last_btmp(struct lslogins_control *ctl, const char *use
 
 }
 
-static int read_utmp(char const *file, size_t *nents, struct utmpx **res)
+static int parse_utmpx(const char *path, size_t *nrecords, struct utmpx **records)
 {
-       size_t n_read = 0, n_alloc = 0;
-       struct utmpx *utmp = NULL, *u;
+       size_t i, imax = 0;
+       struct utmpx *ary = NULL;
+       struct stat st;
 
-       if (utmpxname(file) < 0)
+       *nrecords = 0;
+       *records = NULL;
+
+       if (utmpxname(path) < 0)
                return -errno;
 
-       setutxent();
-       errno = 0;
+       /* optimize allocation according to file size, the realloc() below is
+        * just fallback only */
+       if (stat(path, &st) == 0 && (size_t) st.st_size > sizeof(struct utmpx)) {
+               imax = st.st_size / sizeof(struct utmpx);
+               ary = xmalloc(imax * sizeof(struct utmpx));
+       }
 
-       while ((u = getutxent()) != NULL) {
-               if (n_read == n_alloc) {
-                       n_alloc += 32;
-                       utmp = xrealloc(utmp, n_alloc * sizeof (struct utmpx));
+       for (i = 0; ; i++) {
+               struct utmpx *u;
+               errno = 0;
+               u = getutxent();
+               if (!u) {
+                       if (errno)
+                               goto fail;
+                       break;
                }
-               utmp[n_read++] = *u;
-       }
-       if (!u && errno) {
-               free(utmp);
-               return -errno;
+               if (i == imax)
+                       ary = xrealloc(ary, (imax *= 2) * sizeof(struct utmpx));
+               ary[i] = *u;
        }
 
+       *nrecords = i;
+       *records = ary;
        endutxent();
-
-       *nents = n_read;
-       *res = utmp;
-
        return 0;
-}
-
-static int parse_wtmp(struct lslogins_control *ctl, char *path)
-{
-       int rc = 0;
-
-       rc = read_utmp(path, &ctl->wtmp_size, &ctl->wtmp);
-       if (rc < 0 && errno != EACCES)
-               err(EXIT_FAILURE, "%s", path);
-       return rc;
-}
-
-static int parse_btmp(struct lslogins_control *ctl, char *path)
-{
-       int rc = 0;
-
-       rc = read_utmp(path, &ctl->btmp_size, &ctl->btmp);
-       if (rc < 0 && errno != EACCES)
-               err(EXIT_FAILURE, "%s", path);
-       return rc;
+fail:
+       endutxent();
+       free(ary);
+       if (errno) {
+               if (errno != EACCES)
+                       err(EXIT_FAILURE, "%s", path);
+               return -errno;
+       }
+       return -EINVAL;
 }
 
 static void get_lastlog(struct lslogins_control *ctl, uid_t uid, void *dst, int what)
@@ -1647,11 +1644,11 @@ int main(int argc, char *argv[])
                return EXIT_FAILURE;
 
        if (require_wtmp()) {
-               parse_wtmp(ctl, path_wtmp);
+               parse_utmpx(path_wtmp, &ctl->wtmp_size, &ctl->wtmp);
                ctl->lastlogin_fd = open(path_lastlog, O_RDONLY, 0);
        }
        if (require_btmp())
-               parse_btmp(ctl, path_btmp);
+               parse_utmpx(path_btmp, &ctl->btmp_size, &ctl->btmp);
 
        if (logins || groups)
                get_ulist(ctl, logins, groups);