Commit 53d66608 authored by J. R. Okajima's avatar J. R. Okajima Committed by Linus Torvalds
Browse files

loop: add ioctl to resize a loop device



Add the ability to 'resize' the loop device on the fly.

One practical application is a loop file with XFS filesystem, already
mounted: You can easily enlarge the file (append some bytes) and then call
ioctl(fd, LOOP_SET_CAPACITY, new); The loop driver will learn about the
new size and you can use xfs_growfs later on, which will allow you to use
full capacity of the loop file without the need to unmount.

Test app:

#include <linux/fs.h>
#include <linux/loop.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define _GNU_SOURCE
#include <getopt.h>

char *me;

void usage(FILE *f)
{
	fprintf(f, "%s [options] loop_dev [backend_file]\n"
		"-s, --set new_size_in_bytes\n"
		"\twhen backend_file is given, "
		"it will be expanded too while keeping the original contents\n",
		me);
}

struct option opts[] = {
	{
		.name		= "set",
		.has_arg	= 1,
		.flag		= NULL,
		.val		= 's'
	},
	{
		.name		= "help",
		.has_arg	= 0,
		.flag		= NULL,
		.val		= 'h'
	}
};

void err_size(char *name, __u64 old)
{
	fprintf(stderr, "size must be larger than current %s (%llu)\n",
		name, old);
}

int main(int argc, char *argv[])
{
	int fd, err, c, i, bfd;
	ssize_t ssz;
	size_t sz;
	__u64 old, new, append;
	char a[BUFSIZ];
	struct stat st;
	FILE *out;
	char *backend, *dev;

	err = EINVAL;
	out = stderr;
	me = argv[0];
	new = 0;
	while ((c = getopt_long(argc, argv, "s:h", opts, &i)) != -1) {
		switch (c) {
		case 's':
			errno = 0;
			new = strtoull(optarg, NULL, 0);
			if (errno) {
				err = errno;
				perror(argv[i]);
				goto out;
			}
			break;

		case 'h':
			err = 0;
			out = stdout;
			goto err;

		default:
			perror(argv[i]);
			goto err;
		}
	}

	if (optind < argc)
		dev = argv[optind++];
	else
		goto err;

	fd = open(dev, O_RDONLY);
	if (fd < 0) {
		err = errno;
		perror(dev);
		goto out;
	}

	err = ioctl(fd, BLKGETSIZE64, &old);
	if (err) {
		err = errno;
		perror("ioctl BLKGETSIZE64");
		goto out;
	}

	if (!new) {
		printf("%llu\n", old);
		goto out;
	}

	if (new < old) {
		err = EINVAL;
		err_size(dev, old);
		goto out;
	}

	if (optind < argc) {
		backend = argv[optind++];
		bfd = open(backend, O_WRONLY|O_APPEND);
		if (bfd < 0) {
			err = errno;
			perror(backend);
			goto out;
		}
		err = fstat(bfd, &st);
		if (err) {
			err = errno;
			perror(backend);
			goto out;
		}
		if (new < st.st_size) {
			err = EINVAL;
			err_size(backend, st.st_size);
			goto out;
		}
		append = new - st.st_size;
		sz = sizeof(a);
		while (append > 0) {
			if (append < sz)
				sz = append;
			ssz = write(bfd, a, sz);
			if (ssz != sz) {
				err = errno;
				perror(backend);
				goto out;
			}
			append -= sz;
		}
		err = fsync(bfd);
		if (err) {
			err = errno;
			perror(backend);
			goto out;
		}
	}

	err = ioctl(fd, LOOP_SET_CAPACITY, new);
	if (err) {
		err = errno;
		perror("ioctl LOOP_SET_CAPACITY");
	}
	goto out;

 err:
	usage(out);
 out:
	return err;
}
Signed-off-by: default avatarJ. R. Okajima <hooanon05@yahoo.co.jp>
Signed-off-by: default avatarTomas Matejicek <tomas@slax.org>
Cc: <util-linux-ng@vger.kernel.org>
Cc: Karel Zak <kzak@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 65bd6a9b
......@@ -1192,6 +1192,30 @@ loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
return err;
}
static int loop_set_capacity(struct loop_device *lo, struct block_device *bdev)
{
int err;
sector_t sec;
loff_t sz;
err = -ENXIO;
if (unlikely(lo->lo_state != Lo_bound))
goto out;
err = figure_loop_size(lo);
if (unlikely(err))
goto out;
sec = get_capacity(lo->lo_disk);
/* the width of sector_t may be narrow for bit-shift */
sz = sec;
sz <<= 9;
mutex_lock(&bdev->bd_mutex);
bd_set_size(bdev, sz);
mutex_unlock(&bdev->bd_mutex);
out:
return err;
}
static int lo_ioctl(struct block_device *bdev, fmode_t mode,
unsigned int cmd, unsigned long arg)
{
......@@ -1224,6 +1248,11 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
case LOOP_GET_STATUS64:
err = loop_get_status64(lo, (struct loop_info64 __user *) arg);
break;
case LOOP_SET_CAPACITY:
err = -EPERM;
if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
err = loop_set_capacity(lo, bdev);
break;
default:
err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
}
......@@ -1371,6 +1400,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
lo, (struct compat_loop_info __user *) arg);
mutex_unlock(&lo->lo_ctl_mutex);
break;
case LOOP_SET_CAPACITY:
case LOOP_CLR_FD:
case LOOP_GET_STATUS64:
case LOOP_SET_STATUS64:
......
......@@ -160,5 +160,6 @@ int loop_unregister_transfer(int number);
#define LOOP_SET_STATUS64 0x4C04
#define LOOP_GET_STATUS64 0x4C05
#define LOOP_CHANGE_FD 0x4C06
#define LOOP_SET_CAPACITY 0x4C07
#endif
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