PATH: use a linked list internallysyslinux-5.11-pre1

In retrospect, choosing the colon character as the entry separator for
the PATH directive was not a smart move, as that character is also used
in TFTP-style paths. This conflict manifests as PXELINUX being unable to
find and load files.

An example dnsmasq log looks like,

dnsmasq-tftp: sent /arch/boot/syslinux/lpxelinux.0 to 192.168.0.90
dnsmasq-tftp: file /arch/ldlinux.c32 not found
dnsmasq-tftp: file /arch//ldlinux.c32 not found
dnsmasq-tftp: file /arch//boot/isolinux/ldlinux.c32 not found
dnsmasq-tftp: file /arch//isolinux/ldlinux.c32 not found
dnsmasq-tftp: file /arch//boot/syslinuxldlinux.c32 not found
dnsmasq-tftp: sent /arch//boot/syslinux/ldlinux.c32 to 192.168.0.90
dnsmasq-tftp: error 0 No error, file close received from 192.168.0.90
dnsmasq-tftp: failed sending /arch//boot/syslinux/ldlinux.c32 to 192.168.0.90
dnsmasq-tftp: sent /arch/boot/syslinux/archiso.cfg to 192.168.0.90
dnsmasq-tftp: sent /arch/boot/syslinux/whichsys.c32 to 192.168.0.90
dnsmasq-tftp: file /arch/libcom32.c32 not found
dnsmasq-tftp: file /arch//libcom32.c32 not found
dnsmasq-tftp: file /arch/libcom32.c32 not found
dnsmasq-tftp: file /arch//arch//boot/syslinux/libcom32.c32 not found

The last line of the log is the indication that there's a problem.
Internally, Syslinux adds the location of ldlinux.c32 to PATH by
querying the current working directory once ldlinux.c32 is successfully
loaded. Under PXELINUX that means the initial PATH string will be,

   "::/arch/boot/syslinux/"

The PATH parsing code doesn't know how to correctly parse the "::"
string and hence, the file is searched for relative to the 210 dhcp
option directory - /arch/.

Implement PATH with a linked list which *greatly* simplifies the path
code, and means we no longer have to parse strings backwards and
forwards.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

6 files changed, 109 insertions, 67 deletions

diff --git a/com32/elflink/ldlinux/readconfig.c b/com32/elflink/ldlinux/readconfig.c
index 35b137ea..ab8e240d 100644
--- a/com32/elflink/ldlinux/readconfig.c
+++ b/com32/elflink/ldlinux/readconfig.c
@@ -770,6 +770,46 @@ extern void loadkeys(char *);
 extern char syslinux_banner[];
 extern char copyright_str[];
 
+/*
+ * PATH-based lookup
+ *
+ * Each entry in the PATH directive is separated by a colon, e.g.
+ *
+ *     PATH /bar:/bin/foo:/baz/bar/bin
+ */
+static int parse_path(char *p)
+{
+    struct path_entry *entry;
+    const char *str;
+
+    while (*p) {
+	char *c = p;
+
+	/* Find the next directory */
+	while (*c && *c != ':')
+	    c++;
+
+	str = refstrndup(p, c - p);
+	if (!str)
+	    goto bail;
+
+	entry = path_add(str);
+	refstr_put(str);
+
+	if (!entry)
+	    goto bail;
+
+	if (!*c++)
+	    break;
+	p = c;
+    }
+
+    return 0;
+
+bail:
+    return -1;
+}
+
 static void parse_config_file(FILE * f)
 {
     char line[MAX_LINE], *p, *ep, ch;
@@ -1337,24 +1377,8 @@ do_include:
 	} else if (looking_at(p, "say")) {
 		printf("%s\n", p+4);
 	} else if (looking_at(p, "path")) {
-		/* PATH-based lookup */
-		const char *new_path;
-		char *_p;
-		size_t len, new_len;
-
-		new_path = refstrdup(skipspace(p + 4));
-		len = strlen(PATH);
-		new_len = strlen(new_path);
-		_p = malloc(len + new_len + 2);
-		if (_p) {
-			strncpy(_p, PATH, len);
-			_p[len++] = ':';
-			strncpy(_p + len, new_path, new_len);
-			_p[len + new_len] = '\0';
-			free(PATH);
-			PATH = _p;
-		} else
-			printf("Failed to realloc PATH\n");
+		if (parse_path(skipspace(p + 4)))
+			printf("Failed to parse PATH\n");
 	} else if (looking_at(p, "sendcookies")) {
 		const union syslinux_derivative_info *sdi;
 
diff --git a/com32/lib/sys/module/common.c b/com32/lib/sys/module/common.c
index 8547036b..b763704e 100644
--- a/com32/lib/sys/module/common.c
+++ b/com32/lib/sys/module/common.c
@@ -59,40 +59,28 @@ void print_elf_symbols(struct elf_module *module) {
 
 FILE *findpath(char *name)
 {
+	struct path_entry *entry;
 	char path[FILENAME_MAX];
 	FILE *f;
-	char *p, *n;
-	int i;
 
 	f = fopen(name, "rb"); /* for full path */
 	if (f)
 		return f;
 
-	p = PATH;
-again:
-	i = 0;
-	while (*p && *p != ':' && i < FILENAME_MAX - 1) {
-		path[i++] = *p++;
-	}
-
-	if (*p == ':')
-		p++;
+	list_for_each_entry(entry, &PATH, list) {
+		bool slash = false;
 
-	/* Ensure we have a '/' separator */
-	if (path[i] != '/' && i < FILENAME_MAX - 1)
-		path[i++] = '/';
+		/* Ensure we have a '/' separator */
+		if (entry->str[strlen(entry->str) - 1] != '/')
+			slash = true;
 
-	n = name;
-	while (*n && i < FILENAME_MAX - 1)
-		path[i++] = *n++;
-	path[i] = '\0';
+		snprintf(path, sizeof(path), "%s%s%s",
+			 entry->str, slash ? "/" : "", name);
 
-	f = fopen(path, "rb");
-	if (f)
-		return f;
-
-	if (p >= PATH && p < PATH + strlen(PATH))
-		goto again;
+		f = fopen(path, "rb");
+		if (f)
+			return f;
+	}
 
 	return NULL;
 }
diff --git a/core/elflink/load_env32.c b/core/elflink/load_env32.c
index 0483d865..8551831f 100644
--- a/core/elflink/load_env32.c
+++ b/core/elflink/load_env32.c
@@ -124,14 +124,11 @@ void load_env32(com32sys_t * regs __unused)
 
 	dprintf("Starting 32 bit elf module subsystem...\n");
 
-	PATH = malloc(strlen(CurrentDirName) + 1);
-	if (!PATH) {
+	if (strlen(CurrentDirName) && !path_add(CurrentDirName)) {
 		printf("Couldn't allocate memory for PATH\n");
 		goto out;
 	}
 
-	strcpy(PATH, CurrentDirName);
-
 	init_module_subsystem(&core_module);
 
 	start_ldlinux(1, argv);
@@ -159,30 +156,15 @@ void load_env32(com32sys_t * regs __unused)
 		if (!core_getcwd(path, sizeof(path)))
 			goto out;
 
-		if (!strlen(PATH)) {
-			PATH = realloc(PATH, strlen(path) + 1);
-			if (!PATH) {
-				printf("Couldn't allocate memory for PATH\n");
-				goto out;
-			}
-
-			strcpy(PATH, path);
-		} else {
-			PATH = realloc(PATH, strlen(path) + strlen(PATH) + 2);
-			if (!PATH) {
-				printf("Couldn't allocate memory for PATH\n");
-				goto out;
-			}
-
-			strcat(PATH, ":");
-			strcat(PATH, path);
+		if (!path_add(path)) {
+			printf("Couldn't allocate memory for PATH\n");
+			goto out;
 		}
 
 		start_ldlinux(1, argv);
 	}
 
 out:
-	free(PATH);
 	writestr("\nFailed to load ldlinux.c32");
 }
 
diff --git a/core/fs/fs.c b/core/fs/fs.c
index 1cb4b00a..b6ee19c2 100644
--- a/core/fs/fs.c
+++ b/core/fs/fs.c
@@ -10,8 +10,6 @@
 #include "fs.h"
 #include "cache.h"
 
-__export char *PATH;
-
 /* The currently mounted filesystem */
 __export struct fs_info *this_fs = NULL;		/* Root filesystem */
 
diff --git a/core/include/fs.h b/core/include/fs.h
index c7d0fd75..b5c7f0d9 100644
--- a/core/include/fs.h
+++ b/core/include/fs.h
@@ -1,6 +1,7 @@
 #ifndef FS_H
 #define FS_H
 
+#include <linux/list.h>
 #include <stddef.h>
 #include <stdbool.h>
 #include <string.h>
@@ -182,7 +183,14 @@ static inline struct file *handle_to_file(uint16_t handle)
     return handle ? &files[handle-1] : NULL;
 }
 
-extern char *PATH;
+struct path_entry {
+    struct list_head list;
+    const char *str;
+};
+
+extern struct list_head PATH;
+
+extern struct path_entry *path_add(const char *str);
 
 /* fs.c */
 void pm_mangle_name(com32sys_t *);
diff --git a/core/path.c b/core/path.c
new file mode 100644
index 00000000..8e517ca7
--- /dev/null
+++ b/core/path.c
@@ -0,0 +1,42 @@
+/* ----------------------------------------------------------------------- *
+ *
+ *   Copyright 2013 Intel Corporation; author: Matt Fleming
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ *   Boston MA 02110-1301, USA; either version 2 of the License, or
+ *   (at your option) any later version; incorporated herein by reference.
+ *
+ * ----------------------------------------------------------------------- */
+
+#include <klibc/compiler.h>
+#include <linux/list.h>
+#include <fs.h>
+#include <string.h>
+
+__export LIST_HEAD(PATH);
+
+__export struct path_entry *path_add(const char *str)
+{
+    struct path_entry *entry;
+
+    if (!strlen(str))
+	return NULL;
+
+    entry = malloc(sizeof(*entry));
+    if (!entry)
+	return NULL;
+
+    entry->str = strdup(str);
+    if (!entry->str)
+	goto bail;
+
+    list_add(&entry->list, &PATH);
+
+    return entry;
+
+bail:
+    free(entry);
+    return NULL;
+}