command: add readlink support

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

commands/Kconfig

@@ -220,6 +220,12 @@ config CMD_DIRNAME
 	  Strip last component of file name and store the result in a
 	  environment variable
 
+config CMD_READLINK
+	tristate
+	prompt "readlink"
+	help
+	  read value of a symbolic link
+
 endmenu
 
 menu "console                       "

commands/Makefile

@@ -72,3 +72,4 @@ obj-$(CONFIG_CMD_AUTOMOUNT)	+= automount.o
 obj-$(CONFIG_CMD_GLOBAL)	+= global.o
 obj-$(CONFIG_CMD_BASENAME)	+= basename.o
 obj-$(CONFIG_CMD_DIRNAME)	+= dirname.o
+obj-$(CONFIG_CMD_READLINK)	+= readlink.o

commands/readlink.c

@@ -0,0 +1,80 @@
+/*
+ * readlink.c - read value of a symbolic link
+ *
+ * Copyright (c) 2012 Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <common.h>
+#include <command.h>
+#include <libgen.h>
+#include <environment.h>
+#include <fs.h>
+#include <malloc.h>
+#include <getopt.h>
+
+static int do_readlink(int argc, char *argv[])
+{
+	char realname[PATH_MAX];
+	int canonicalize = 0;
+	int opt;
+
+	memset(realname, 0, PATH_MAX);
+
+	while ((opt = getopt(argc, argv, "f")) > 0) {
+		switch (opt) {
+		case 'f':
+			canonicalize = 1;
+			break;
+		}
+	}
+
+	if (argc < optind + 2)
+		return COMMAND_ERROR_USAGE;
+
+	if (readlink(argv[optind], realname, PATH_MAX - 1) < 0)
+		goto err;
+
+	if (canonicalize) {
+		char *buf = normalise_link(argv[optind], realname);
+
+		if (!buf)
+			goto err;
+		setenv(argv[optind + 1], buf);
+		free(buf);
+	} else {
+		setenv(argv[optind + 1], realname);
+	}
+
+	return 0;
+err:
+	setenv(argv[optind + 1], "");
+	return 1;
+}
+
+BAREBOX_CMD_HELP_START(readlink)
+BAREBOX_CMD_HELP_USAGE("readlink [-f] FILE REALNAME\n")
+BAREBOX_CMD_HELP_SHORT("read value of a symbolic link and store into $REALNAME\n")
+BAREBOX_CMD_HELP_SHORT("-f canonicalize by following first symlink");
+BAREBOX_CMD_HELP_END
+
+BAREBOX_CMD_START(readlink)
+	.cmd		= do_readlink,
+	.usage		= "read value of a symbolic link",
+	BAREBOX_CMD_HELP(cmd_readlink_help)
+BAREBOX_CMD_END