Add chroot(1).

utils/.gitignore

@@ -1,6 +1,7 @@
 *.o
 calc
 cat
+chroot
 chvideomode
 clear
 colormake

utils/Makefile

@@ -17,6 +17,7 @@ CXXFLAGS:=$(CXXFLAGS) -Wall -Wextra -fno-exceptions -fno-rtti
 BINARIES:=\
 calc \
 cat \
+chroot \
 chvideomode \
 clear \
 colormake \

utils/chroot.cpp

@@ -0,0 +1,116 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    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, either version 3 of the License, or (at your option)
+    any later version.
+
+    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, see <http://www.gnu.org/licenses/>.
+
+    chroot.cpp
+    Runs a process with another root directory.
+
+*******************************************************************************/
+
+#include <errno.h>
+#include <error.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#if !defined(VERSIONSTR)
+#define VERSIONSTR "unknown version"
+#endif
+
+void CompactArguments(int* argc, char*** argv)
+{
+	for ( int i = 0; i < *argc; i++ )
+	while ( i < *argc && !(*argv)[i] )
+	{
+		for ( int n = i; n < *argc; n++ )
+			(*argv)[n] = (*argv)[n+1];
+		(*argc)--;
+	}
+}
+
+void Usage(FILE* fp, const char* argv0)
+{
+	fprintf(fp, "Usage: %s [OPTION]... ROOT [CMD] [ARGUMENT...]\n", argv0);
+}
+
+void Help(FILE* fp, const char* argv0)
+{
+	Usage(fp, argv0);
+}
+
+void Version(FILE* fp, const char* argv0)
+{
+	fprintf(fp, "%s (Sortix) %s\n", argv0, VERSIONSTR);
+	fprintf(fp, "License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.\n");
+	fprintf(fp, "This is free software: you are free to change and redistribute it.\n");
+	fprintf(fp, "There is NO WARRANTY, to the extent permitted by law.\n");
+}
+
+int main(int argc, char* argv[])
+{
+	const char* argv0 = argv[0];
+	for ( int i = 1; i < argc; i++ )
+	{
+		const char* arg = argv[i];
+		if ( arg[0] != '-' )
+			continue;
+		argv[i] = NULL;
+		if ( !strcmp(arg, "--") )
+			break;
+		if ( arg[1] != '-' )
+		{
+			while ( char c = *++arg ) switch ( c )
+			{
+			default:
+				fprintf(stderr, "%s: unknown option -- '%c'\n", argv0, c);
+				Usage(stderr, argv0);
+				exit(1);
+			}
+		}
+		else if ( !strcmp(arg, "--help") ) { Help(stdout, argv0); exit(0); }
+		else if ( !strcmp(arg, "--usage") ) { Usage(stdout, argv0); exit(0); }
+		else if ( !strcmp(arg, "--version") ) { Version(stdout, argv0); exit(0); }
+		else
+		{
+			fprintf(stderr, "%s: unknown option: %s\n", argv0, arg);
+			Usage(stderr, argv0);
+			exit(1);
+		}
+	}
+
+	CompactArguments(&argc, &argv);
+
+	if ( argc < 2 )
+	{
+		error(0, 0, "missing operand, expected new root directory");
+		Usage(stdout, argv0);
+		exit(0);
+	}
+
+	if ( chroot(argv[1]) != 0 )
+		error(1, errno, "`%s'", argv[1]);
+
+	if ( chdir("/.") != 0 )
+		error(1, errno, "chdir: `%s/.'", argv[1]);
+
+	char* default_argv[] = { (char*) "sh", (char*) NULL };
+
+	char** exec_argv = 3 <= argc ? argv + 2 : default_argv;
+	execvp(exec_argv[0], exec_argv);
+
+	error(127, errno, "`%s'", exec_argv[0]);
+}