Re: [Qemu-devel] [PATCH][UPDATED] Fix path mangling in linux-user/path.c

["Kirill A. Shutemov" <k.shutemov@velesys.com>]

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On [Tue, 22.05.2007 02:22], Lauri Leukkunen wrote:
> Attached patch fixes the linux-user path mangling code for use with
> real target root filesystems that have nasty symlinks and lots of
> files. The old code is terribly slow and can easily end up going
> through the entire host system /usr hierarchy in a recursive loop.
> 
> Compared to the previous version of this patch, fixes an issue with
> attempting to free() a pointer returned by GNU basename().

My patch to solve same problems attached

-- 
Regards,  Kirill A. Shutemov
 + Belarus, Minsk
 + Velesys LLC, http://www.velesys.com/
 + ALT Linux Team, http://www.altlinux.com/

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--- qemu/linux-user/path.c
+++ qemu/linux-user/path.c
@@ -1,147 +1,81 @@
 /* Code to mangle pathnames into those matching a given prefix.
    eg. open("/lib/foo.so") => open("/usr/gnemul/i386-linux/lib/foo.so");
-
-   The assumption is that this area does not change.
 */
 #include <sys/types.h>
-#include <dirent.h>
+#include <sys/stat.h>
 #include <unistd.h>
-#include <stdlib.h>
 #include <string.h>
-#include <errno.h>
 #include <stdio.h>
 #include "qemu.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];
+struct path_list_head {
+	    struct path_list_head *next;
+		char* path;
 };
 
-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);
-
-static struct pathelem *new_entry(const char *root,
-				  struct pathelem *parent,
-				  const char *name)
-{
-    struct pathelem *new = malloc(sizeof(*new));
-    new->name = strdup(name);
-    asprintf(&new->pathname, "%s/%s", root, name);
-    new->num_entries = 0;
-    return new;
-}
-
-#define streq(a,b) (strcmp((a), (b)) == 0)
-
-static struct pathelem *add_dir_maybe(struct pathelem *path)
-{
-    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);
-	    }
-	}
-        closedir(dir);
-    }
-    return path;
-}
-
-static struct pathelem *add_entry(struct pathelem *root, const char *name)
-{
-    root->num_entries++;
-
-    root = realloc(root, sizeof(*root)
-		   + sizeof(root->entries[0])*root->num_entries);
-
-    root->entries[root->num_entries-1] = new_entry(root->pathname, root, name);
-    root->entries[root->num_entries-1]
-	= add_dir_maybe(root->entries[root->num_entries-1]);
-    return root;
-}
-
-/* This needs to be done after tree is stabalized (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);
-}
+static struct path_list_head* list_head;
 
 void init_paths(const char *prefix)
 {
     if (prefix[0] != '/' ||
-        prefix[0] == '\0' ||
-        !strcmp(prefix, "/"))
+            prefix[0] == '\0' ||
+            !strcmp(prefix, "/"))
         return;
 
-    base = new_entry("", NULL, prefix+1);
-    base = add_dir_maybe(base);
-    if (base->num_entries == 0) {
-        free (base);
-        base = NULL;
-    } else {
-        set_parents(base, base);
-    }
-}
+	list_head = malloc(sizeof(struct path_list_head));
 
-/* 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;
+	/* first element of list is prefix */
+	list_head->path = strdup(prefix);
+	list_head->next = NULL;
 }
 
 /* Look for path in emulation dir, otherwise return name. */
 const char *path(const char *name)
 {
+	struct path_list_head *list = list_head;
+	int path_length = strlen(list_head->path) + strlen(name) + 1;
+	char *newname = malloc(path_length);
+	struct stat buf;
+	const char * result = name;
+
     /* Only do absolute paths: quick and dirty, but should mostly be OK.
        Could do relative by tracking cwd. */
-    if (!base || name[0] != '/')
-	return name;
-
-    return follow_path(base, name) ?: name;
+    if (!list_head || result[0] != '/')
+		goto exit;
+
+	strncpy(newname, list_head->path, path_length);
+	strncat(newname, name, path_length);
+
+	/* look for place where path should be present */
+	while ( list->next && (strcmp(list->next->path, newname) < 0) )
+		list = list->next;
+
+	/* if there is no path in list */
+	if ( !list->next || strcmp(list->next->path, newname) )	{
+		/* add element to list if path exist in emulation dir */
+		if ( !stat(newname, &buf) )
+		{
+			struct path_list_head *new;
+
+			new = malloc(sizeof(struct path_list_head));
+			new->path = strdup(newname);
+			new->next = list->next;
+			list->next = new;
+			result = new->path;
+		}
+
+	} else if ( stat(list->next->path, &buf) ) {
+		/* remove element from list if path doesn't exist in emulation dir */
+		struct path_list_head* tmp;
+
+		tmp = list->next;
+		list->next = tmp->next;
+		free(tmp->path);
+		free(tmp);
+	} else
+		result = list->next->path;
+
+exit:
+	free(newname);
+	return result;
 }

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