build-sys: move pivot_root(8) to sys-utils

This patch moves pivot_root.{8,c) from mount/ to sys-utils/ directory.
There is not ant relation between pivot_root source code and the rest of
code in the mount.

Signed-off-by: Karel Zak <kzak@redhat.com>

4 files changed, 120 insertions, 14 deletions

diff --git a/sys-utils/.gitignore b/sys-utils/.gitignore
index fb6e433b6..c47cd077a 100644
--- a/sys-utils/.gitignore
+++ b/sys-utils/.gitignore
@@ -1,40 +1,41 @@
+arch
 ctrlaltdel
 cytune
 dmesg
 flock
+i386.8
+ia64.8
+ipcmk
 ipcrm
 ipcs
-ipcmk
 ldattach
-readprofile
-renice
-rtcwake
-lscpu
-setarch
-setsid
-tunelp
-arch
-vidmode.8
-ramsize.8
-rdev
-i386.8
-ia64.8
 linux32.8
 linux64.8
+lscpu
 mips32.8
 mips64.8
 mips.8
 parisc32.8
 parisc64.8
 parisc.8
+pivot_root
 ppc32.8
 ppc64.8
 ppc.8
+ramsize.8
+rdev
+readprofile
+renice
 rootflags.8
+rtcwake
 s390.8
 s390x.8
+setarch
+setsid
 sparc32.8
 sparc32bash.8
 sparc64.8
 sparc.8
+tunelp
+vidmode.8
 x86_64.8
diff --git a/sys-utils/Makefile.am b/sys-utils/Makefile.am
index 0dbbb482c..b4c6ac601 100644
--- a/sys-utils/Makefile.am
+++ b/sys-utils/Makefile.am
@@ -23,6 +23,11 @@ tunelp_SOURCES = tunelp.c lp.h
 
 info_TEXINFOS = ipc.texi
 
+if HAVE_PIVOT_ROOT
+sbin_PROGRAMS += pivot_root
+dist_man_MANS += pivot_root.8
+endif
+
 if BUILD_ARCH
 bin_PROGRAMS += arch
 dist_man_MANS += arch.1
diff --git a/sys-utils/pivot_root.8 b/sys-utils/pivot_root.8
new file mode 100644
index 000000000..92b12555d
--- /dev/null
+++ b/sys-utils/pivot_root.8
@@ -0,0 +1,68 @@
+.TH PIVOT_ROOT 8 "Feb 23, 2000" "Linux" "Maintenance Commands"
+.SH NAME
+pivot_root \- change the root file system
+.SH SYNOPSIS
+.B pivot_root
+.RB \fInew_root\fP
+.RB \fIput_old\fP
+.SH DESCRIPTION
+\fBpivot_root\fP moves the root file system of the current process to the
+directory \fIput_old\fP and makes \fInew_root\fP the new root file system.
+Since \fBpivot_root(8)\fP simply calls \fBpivot_root(2)\fP, we refer to
+the man page of the latter for further details.
+
+Note that, depending on the implementation of \fBpivot_root\fP, root and
+cwd of the caller may or may not change. The following is a sequence for
+invoking \fBpivot_root\fP that works in either case, assuming that
+\fBpivot_root\fP and \fBchroot\fP are in the current \fBPATH\fP:
+.sp
+cd \fInew_root\fP
+.br
+pivot_root . \fIput_old\fP
+.br
+exec chroot . \fIcommand\fP
+.sp
+Note that \fBchroot\fP must be available under the old root and under the new
+root, because \fBpivot_root\fP may or may not have implicitly changed the
+root directory of the shell.
+
+Note that \fBexec chroot\fP changes the running executable, which is
+necessary if the old root directory should be unmounted afterwards.
+Also note that standard input, output, and error may still point to a
+device on the old root file system, keeping it busy. They can easily be
+changed when invoking \fBchroot\fP (see below; note the absence of
+leading slashes to make it work whether \fBpivot_root\fP has changed the
+shell's root or not).
+.SH EXAMPLES
+Change the root file system to /dev/hda1 from an interactive shell:
+.sp
+.nf
+mount /dev/hda1 /new-root
+cd /new-root
+pivot_root . old-root
+exec chroot . sh <dev/console >dev/console 2>&1
+umount /old-root
+.fi
+.sp
+Mount the new root file system over NFS from 10.0.0.1:/my_root and run
+\fBinit\fP:
+.sp
+.nf
+ifconfig lo 127.0.0.1 up   # for portmap
+# configure Ethernet or such
+portmap   # for lockd (implicitly started by mount)
+mount -o ro 10.0.0.1:/my_root /mnt
+killall portmap   # portmap keeps old root busy
+cd /mnt
+pivot_root . old_root
+exec chroot . sh -c 'umount /old_root; exec /sbin/init' \\
+  <dev/console >dev/console 2>&1
+.fi
+.SH "SEE ALSO"
+.BR chroot(1),
+.BR mount(8),
+.BR pivot_root(2),
+.BR umount(8)
+.SH AVAILABILITY
+The pivot_root command is part of the util-linux-ng package and is available from
+ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
diff --git a/sys-utils/pivot_root.c b/sys-utils/pivot_root.c
new file mode 100644
index 000000000..ba2dbbed0
--- /dev/null
+++ b/sys-utils/pivot_root.c
@@ -0,0 +1,32 @@
+/* pivot_root.c - Change the root file system */
+
+/* Written 2000 by Werner Almesberger */
+
+#include <stdio.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#define pivot_root(new_root,put_old) syscall(SYS_pivot_root,new_root,put_old)
+
+#if 0
+/*
+ * With kernelheaders 2.3.41 or later, and ancient libc, try the following.
+ */
+#include <errno.h>
+#include <linux/unistd.h>
+static
+_syscall2(int,pivot_root,const char *,new_root,const char *,put_old)
+#endif
+
+int main(int argc, const char **argv)
+{
+	if (argc != 3) {
+		fprintf(stderr, "usage: %s new_root put_old\n", argv[0]);
+		return 1;
+	}
+	if (pivot_root(argv[1],argv[2]) < 0) {
+		perror("pivot_root");
+		return 1;
+	}
+	return 0;
+}