util/path: Do not cache all filenames at startup

If one uses -L $PATH to point to a full chroot, the startup time
is significant.  In addition, the existing probing algorithm fails
to handle symlink loops.

Instead, probe individual paths on demand.  Cache both positive
and negative results within $PATH, so that any one filename is
probed only once.

Use glib filename functions for clarity.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20190519201953.20161-2-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

util/path.c

@@ -8,170 +8,63 @@
 #include <dirent.h>
 #include "qemu/cutils.h"
 #include "qemu/path.h"
+#include "qemu/thread.h"
 
-struct pathelem
-{
-    /* Name of this, eg. lib */
-    char *name;
-    /* Full path name, eg. /usr/gnemul/x86-linux/lib. */
-    char *pathname;
-    struct pathelem *parent;
-    /* Children */
-    unsigned int num_entries;
-    struct pathelem *entries[0];
-};
-
-static struct pathelem *base;
-
-/* First N chars of S1 match S2, and S2 is N chars long. */
-static int strneq(const char *s1, unsigned int n, const char *s2)
-{
-    unsigned int i;
-
-    for (i = 0; i < n; i++)
-        if (s1[i] != s2[i])
-            return 0;
-    return s2[i] == 0;
-}
-
-static struct pathelem *add_entry(struct pathelem *root, const char *name,
-                                  unsigned type);
+static const char *base;
+static GHashTable *hash;
+static QemuMutex lock;
 
-static struct pathelem *new_entry(const char *root,
-                                  struct pathelem *parent,
-                                  const char *name)
-{
-    struct pathelem *new = g_malloc(sizeof(*new));
-    new->name = g_strdup(name);
-    new->pathname = g_strdup_printf("%s/%s", root, name);
-    new->num_entries = 0;
-    return new;
-}
-
-#define streq(a,b) (strcmp((a), (b)) == 0)
-
-/* Not all systems provide this feature */
-#if defined(DT_DIR) && defined(DT_UNKNOWN) && defined(DT_LNK)
-# define dirent_type(dirent) ((dirent)->d_type)
-# define is_dir_maybe(type) \
-    ((type) == DT_DIR || (type) == DT_UNKNOWN || (type) == DT_LNK)
-#else
-# define dirent_type(dirent) (1)
-# define is_dir_maybe(type)  (type)
-#endif
-
-static struct pathelem *add_dir_maybe(struct pathelem *path)
+void init_paths(const char *prefix)
 {
-    DIR *dir;
-
-    if ((dir = opendir(path->pathname)) != NULL) {
-        struct dirent *dirent;
-
-        while ((dirent = readdir(dir)) != NULL) {
-            if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){
-                path = add_entry(path, dirent->d_name, dirent_type(dirent));
-            }
-        }
-        closedir(dir);
+    if (prefix[0] == '\0' || !strcmp(prefix, "/")) {
+        return;
     }
-    return path;
-}
-
-static struct pathelem *add_entry(struct pathelem *root, const char *name,
-                                  unsigned type)
-{
-    struct pathelem **e;
-
-    root->num_entries++;
-
-    root = g_realloc(root, sizeof(*root)
-                   + sizeof(root->entries[0])*root->num_entries);
-    e = &root->entries[root->num_entries-1];
 
-    *e = new_entry(root->pathname, root, name);
-    if (is_dir_maybe(type)) {
-        *e = add_dir_maybe(*e);
+    if (prefix[0] == '/') {
+        base = g_strdup(prefix);
+    } else {
+        char *cwd = g_get_current_dir();
+        base = g_build_filename(cwd, prefix, NULL);
+        g_free(cwd);
     }
 
-    return root;
-}
-
-/* This needs to be done after tree is stabilized (ie. no more reallocs!). */
-static void set_parents(struct pathelem *child, struct pathelem *parent)
-{
-    unsigned int i;
-
-    child->parent = parent;
-    for (i = 0; i < child->num_entries; i++)
-        set_parents(child->entries[i], child);
+    hash = g_hash_table_new(g_str_hash, g_str_equal);
+    qemu_mutex_init(&lock);
 }
 
-/* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */
-static const char *
-follow_path(const struct pathelem *cursor, const char *name)
-{
-    unsigned int i, namelen;
-
-    name += strspn(name, "/");
-    namelen = strcspn(name, "/");
-
-    if (namelen == 0)
-        return cursor->pathname;
-
-    if (strneq(name, namelen, ".."))
-        return follow_path(cursor->parent, name + namelen);
-
-    if (strneq(name, namelen, "."))
-        return follow_path(cursor, name + namelen);
-
-    for (i = 0; i < cursor->num_entries; i++)
-        if (strneq(name, namelen, cursor->entries[i]->name))
-            return follow_path(cursor->entries[i], name + namelen);
-
-    /* Not found */
-    return NULL;
-}
-
-void init_paths(const char *prefix)
+/* Look for path in emulation dir, otherwise return name. */
+const char *path(const char *name)
 {
-    char pref_buf[PATH_MAX];
-
-    if (prefix[0] == '\0' ||
-        !strcmp(prefix, "/"))
-        return;
+    gpointer key, value;
+    const char *ret;
 
-    if (prefix[0] != '/') {
-        char *cwd = getcwd(NULL, 0);
-        size_t pref_buf_len = sizeof(pref_buf);
+    /* Only do absolute paths: quick and dirty, but should mostly be OK.  */
+    if (!base || !name || name[0] != '/') {
+        return name;
+    }
 
-        if (!cwd)
-            abort();
-        pstrcpy(pref_buf, sizeof(pref_buf), cwd);
-        pstrcat(pref_buf, pref_buf_len, "/");
-        pstrcat(pref_buf, pref_buf_len, prefix);
-        free(cwd);
-    } else
-        pstrcpy(pref_buf, sizeof(pref_buf), prefix + 1);
+    qemu_mutex_lock(&lock);
 
-    base = new_entry("", NULL, pref_buf);
-    base = add_dir_maybe(base);
-    if (base->num_entries == 0) {
-        g_free(base->pathname);
-        g_free(base->name);
-        g_free(base);
-        base = NULL;
+    /* Have we looked up this file before?  */
+    if (g_hash_table_lookup_extended(hash, name, &key, &value)) {
+        ret = value ? value : name;
     } else {
-        set_parents(base, base);
+        char *save = g_strdup(name);
+        char *full = g_build_filename(base, name, NULL);
+
+        /* Look for the path; record the result, pass or fail.  */
+        if (access(full, F_OK) == 0) {
+            /* Exists.  */
+            g_hash_table_insert(hash, save, full);
+            ret = full;
+        } else {
+            /* Does not exist.  */
+            g_free(full);
+            g_hash_table_insert(hash, save, NULL);
+            ret = name;
+        }
     }
-}
-
-/* Look for path in emulation dir, otherwise return name. */
-const char *path(const char *name)
-{
-    /* Only do absolute paths: quick and dirty, but should mostly be OK.
-       Could do relative by tracking cwd. */
-    if (!base || !name || name[0] != '/')
-        return name;
 
-    return follow_path(base, name) ?: name;
+    qemu_mutex_unlock(&lock);
+    return ret;
 }