busybox/util-linux/umount.c

/* vi: set sw=4 ts=4: */
/*
 * Mini umount implementation for busybox
 *
 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 * Copyright (C) 2005 by Rob Landley <rob@landley.net>
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config UMOUNT
//config:	bool "umount (5.1 kb)"
//config:	default y
//config:	help
//config:	When you want to remove a mounted filesystem from its current mount
//config:	point, for example when you are shutting down the system, the
//config:	'umount' utility is the tool to use. If you enabled the 'mount'
//config:	utility, you almost certainly also want to enable 'umount'.
//config:
//config:config FEATURE_UMOUNT_ALL
//config:	bool "Support -a (unmount all)"
//config:	default y
//config:	depends on UMOUNT
//config:	help
//config:	Support -a option to unmount all currently mounted filesystems.

//applet:IF_UMOUNT(APPLET_NOEXEC(umount, umount, BB_DIR_BIN, BB_SUID_DROP, umount))
/*
 * On one hand, in some weird situations you'd want umount
 * to not do anything surprising, to behave as a usual fork+execed executable.
 *
 * OTOH, there can be situations where execing would not succeed, or even hang
 * (say, if executable is on a filesystem which is in trouble and accesses to it
 * block in kernel).
 * In this case, you might be actually happy if your standalone bbox shell
 * does not fork+exec, but only forks and calls umount_main() which it already has!
 * Let's go with NOEXEC.
 *
 * bb_common_bufsiz1 usage here is safe wrt NOEXEC: not expecting it to be zeroed.
 */

//kbuild:lib-$(CONFIG_UMOUNT) += umount.o

//usage:#define umount_trivial_usage
//usage:       "[-rlf"IF_FEATURE_MTAB_SUPPORT("m")IF_FEATURE_MOUNT_LOOP("d")IF_FEATURE_UMOUNT_ALL("a")"] [-t FSTYPE] FILESYSTEM|DIRECTORY"
//usage:#define umount_full_usage "\n\n"
//usage:       "Unmount filesystems\n"
//usage:	IF_FEATURE_UMOUNT_ALL(
//usage:     "\n	-a	Unmount all filesystems" IF_FEATURE_MTAB_SUPPORT(" in /etc/mtab")
//usage:	)
//usage:	IF_FEATURE_MTAB_SUPPORT(
//usage:     "\n	-n	Don't erase /etc/mtab entries"
//usage:	)
//usage:     "\n	-r	Remount devices read-only if mount is busy"
//usage:     "\n	-l	Lazy umount (detach filesystem)"
//usage:     "\n	-f	Force umount (i.e., unreachable NFS server)"
//usage:	IF_FEATURE_MOUNT_LOOP(
//usage:     "\n	-d	Free loop device if it has been used"
//usage:	)
//usage:     "\n	-t FSTYPE[,...]	Unmount only these filesystem type(s)"
//usage:
//usage:#define umount_example_usage
//usage:       "$ umount /dev/hdc1\n"

#include <mntent.h>
#include <sys/mount.h>
#ifndef MNT_DETACH
# define MNT_DETACH 0x00000002
#endif
#include "libbb.h"
#include "common_bufsiz.h"

#if defined(__dietlibc__)
// TODO: This does not belong here.
/* 16.12.2006, Sampo Kellomaki (sampo@iki.fi)
 * dietlibc-0.30 does not have implementation of getmntent_r() */
static struct mntent *getmntent_r(FILE* stream, struct mntent* result,
		char* buffer UNUSED_PARAM, int bufsize UNUSED_PARAM)
{
	struct mntent* ment = getmntent(stream);
	return memcpy(result, ment, sizeof(*ment));
}
#endif

/* ignored: -c -v -i */
#define OPTION_STRING           "fldnrat:" "cvi"
#define OPT_FORCE               (1 << 0) // Same as MNT_FORCE
#define OPT_LAZY                (1 << 1) // Same as MNT_DETACH
#define OPT_FREELOOP            (1 << 2)
#define OPT_NO_MTAB             (1 << 3)
#define OPT_REMOUNT             (1 << 4)
#define OPT_ALL                 (ENABLE_FEATURE_UMOUNT_ALL ? (1 << 5) : 0)

int umount_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int umount_main(int argc UNUSED_PARAM, char **argv)
{
	int doForce;
	struct mntent me;
	FILE *fp;
	char *fstype = NULL;
	int status = EXIT_SUCCESS;
	unsigned opt;
	struct mtab_list {
		char *dir;
		char *device;
		struct mtab_list *next;
	} *mtl, *m;

	opt = getopt32(argv, OPTION_STRING, &fstype);
	//argc -= optind;
	argv += optind;

	// MNT_FORCE and MNT_DETACH (from linux/fs.h) must match
	// OPT_FORCE and OPT_LAZY.
	BUILD_BUG_ON(OPT_FORCE != MNT_FORCE || OPT_LAZY != MNT_DETACH);
	doForce = opt & (OPT_FORCE|OPT_LAZY);

	/* Get a list of mount points from mtab.  We read them all in now mostly
	 * for umount -a (so we don't have to worry about the list changing while
	 * we iterate over it, or about getting stuck in a loop on the same failing
	 * entry.  Notice that this also naturally reverses the list so that -a
	 * umounts the most recent entries first. */
	m = mtl = NULL;

	// If we're umounting all, then m points to the start of the list and
	// the argument list should be empty (which will match all).
	fp = setmntent(bb_path_mtab_file, "r");
	if (!fp) {
		if (opt & OPT_ALL)
			bb_error_msg_and_die("can't open '%s'", bb_path_mtab_file);
	} else {
		setup_common_bufsiz();
		while (getmntent_r(fp, &me, bb_common_bufsiz1, COMMON_BUFSIZE)) {
			/* Match fstype (fstype==NULL matches always) */
			if (!fstype_matches(me.mnt_type, fstype))
				continue;
			m = xzalloc(sizeof(*m));
			m->next = mtl;
			m->device = xstrdup(me.mnt_fsname);
			m->dir = xstrdup(me.mnt_dir);
			mtl = m;
		}
		endmntent(fp);
	}

	// If we're not umounting all, we need at least one argument.
	// Note: "-t FSTYPE" does not imply -a.
	if (!(opt & OPT_ALL)) {
		if (!argv[0])
			bb_show_usage();
		m = NULL;
	}

	// Loop through everything we're supposed to umount, and do so.
	for (;;) {
		int curstat;
		char *zapit = *argv;
		char *path;

		// Do we already know what to umount this time through the loop?
		if (m)
			path = xstrdup(m->dir);
		// For umount -a, end of mtab means time to exit.
		else if (opt & OPT_ALL)
			break;
		// Use command line argument (and look it up in mtab list)
		else {
			if (!zapit)
				break;
			argv++;
			path = xmalloc_realpath(zapit);
			if (path) {
				for (m = mtl; m; m = m->next)
					if (strcmp(path, m->dir) == 0 || strcmp(path, m->device) == 0)
						break;
			}
		}
		// If we couldn't find this sucker in /etc/mtab, punt by passing our
		// command line argument straight to the umount syscall.  Otherwise,
		// umount the directory even if we were given the block device.
		if (m) zapit = m->dir;

// umount from util-linux 2.22.2 does not do this:
// umount -f uses umount2(MNT_FORCE) immediately,
// not trying umount() first.
// (Strangely, umount -fl ignores -f: it is equivalent to umount -l.
// We do pass both flags in this case)
#if 0
		// Let's ask the thing nicely to unmount.
		curstat = umount(zapit);

		// Unmount with force and/or lazy flags, if necessary.
		if (curstat && doForce)
#endif
			curstat = umount2(zapit, doForce);

		// If still can't umount, maybe remount read-only?
		if (curstat) {
			if ((opt & OPT_REMOUNT) && errno == EBUSY && m) {
				// Note! Even if we succeed here, later we should not
				// free loop device or erase mtab entry!
				const char *msg = "%s busy - remounted read-only";
				curstat = mount(m->device, zapit, NULL, MS_REMOUNT|MS_RDONLY, NULL);
				if (curstat) {
					msg = "can't remount %s read-only";
					status = EXIT_FAILURE;
				}
				bb_error_msg(msg, m->device);
			} else {
				status = EXIT_FAILURE;
				bb_perror_msg("can't unmount %s", zapit);
			}
		} else {
			// De-allocate the loop device.  This ioctl should be ignored on
			// any non-loop block devices.
			if (ENABLE_FEATURE_MOUNT_LOOP && (opt & OPT_FREELOOP) && m)
				del_loop(m->device);
			if (ENABLE_FEATURE_MTAB_SUPPORT && !(opt & OPT_NO_MTAB) && m)
				erase_mtab(m->dir);
		}

		// Find next matching mtab entry for -a or umount /dev
		// Note this means that "umount /dev/blah" will unmount all instances
		// of /dev/blah, not just the most recent.
		if (m) {
			while ((m = m->next) != NULL)
				// NB: if m is non-NULL, path is non-NULL as well
				if ((opt & OPT_ALL) || strcmp(path, m->device) == 0)
					break;
		}
		free(path);
	}

	// Free mtab list if necessary
	if (ENABLE_FEATURE_CLEAN_UP) {
		while (mtl) {
			m = mtl->next;
			free(mtl->device);
			free(mtl->dir);
			free(mtl);
			mtl = m;
		}
	}

	return status;
}