Adding upstream version 2.39.3.upstream/2.39.3

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1935 insertions, 0 deletions

diff --git a/lib/loopdev.c b/lib/loopdev.c
new file mode 100644
index 0000000..dd9ead3
--- /dev/null
+++ b/lib/loopdev.c
@@ -0,0 +1,1935 @@
+
+/*
+ * No copyright is claimed.  This code is in the public domain; do with
+ * it what you wish.
+ *
+ * Written by Karel Zak <kzak@redhat.com>
+ *
+ * -- based on mount/losetup.c
+ *
+ * Simple library for work with loop devices.
+ *
+ *  - requires kernel 2.6.x
+ *  - reads info from /sys/block/loop<N>/loop/<attr> (new kernels)
+ *  - reads info by ioctl
+ *  - supports *unlimited* number of loop devices
+ *  - supports /dev/loop<N> as well as /dev/loop/<N>
+ *  - minimize overhead (fd, loopinfo, ... are shared for all operations)
+ *  - setup (associate device and backing file)
+ *  - delete (dis-associate file)
+ *  - old LOOP_{SET,GET}_STATUS (32bit) ioctls are unsupported
+ *  - extendible
+ */
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <ctype.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <inttypes.h>
+#include <dirent.h>
+
+#include "linux_version.h"
+#include "c.h"
+#include "sysfs.h"
+#include "pathnames.h"
+#include "loopdev.h"
+#include "canonicalize.h"
+#include "blkdev.h"
+#include "debug.h"
+#include "fileutils.h"
+
+#define LOOPDEV_MAX_TRIES	10
+
+/*
+ * Debug stuff (based on include/debug.h)
+ */
+static UL_DEBUG_DEFINE_MASK(loopdev);
+UL_DEBUG_DEFINE_MASKNAMES(loopdev) = UL_DEBUG_EMPTY_MASKNAMES;
+
+#define LOOPDEV_DEBUG_INIT	(1 << 1)
+#define LOOPDEV_DEBUG_CXT	(1 << 2)
+#define LOOPDEV_DEBUG_ITER	(1 << 3)
+#define LOOPDEV_DEBUG_SETUP	(1 << 4)
+
+#define DBG(m, x)       __UL_DBG(loopdev, LOOPDEV_DEBUG_, m, x)
+#define ON_DBG(m, x)    __UL_DBG_CALL(loopdev, LOOPDEV_DEBUG_, m, x)
+
+#define UL_DEBUG_CURRENT_MASK	UL_DEBUG_MASK(loopdev)
+#include "debugobj.h"
+
+static void loopdev_init_debug(void)
+{
+	if (loopdev_debug_mask)
+		return;
+	__UL_INIT_DEBUG_FROM_ENV(loopdev, LOOPDEV_DEBUG_, 0, LOOPDEV_DEBUG);
+}
+
+/*
+ * see loopcxt_init()
+ */
+#define loopcxt_ioctl_enabled(_lc)	(!((_lc)->flags & LOOPDEV_FL_NOIOCTL))
+#define loopcxt_sysfs_available(_lc)	(!((_lc)->flags & LOOPDEV_FL_NOSYSFS)) \
+					 && !loopcxt_ioctl_enabled(_lc)
+
+/*
+ * Calls @x and repeat on EAGAIN
+ */
+#define repeat_on_eagain(x) __extension__ ({			\
+		int _c = 0, _e;					\
+		do {						\
+			errno = 0;				\
+			_e = x;					\
+			if (_e == 0 || errno != EAGAIN)		\
+				break;				\
+			if (_c >= LOOPDEV_MAX_TRIES)		\
+				break;				\
+			xusleep(250000);			\
+			_c++;					\
+		} while (1);					\
+		_e == 0 ? 0 : errno ? -errno : -1;		\
+	})
+
+/*
+ * @lc: context
+ * @device: device name, absolute device path or NULL to reset the current setting
+ *
+ * Sets device, absolute paths (e.g. "/dev/loop<N>") are unchanged, device
+ * names ("loop<N>") are converted to the path (/dev/loop<N> or to
+ * /dev/loop/<N>)
+ *
+ * This sets the device name, but does not check if the device exists!
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_set_device(struct loopdev_cxt *lc, const char *device)
+{
+	if (!lc)
+		return -EINVAL;
+
+	if (lc->fd >= 0) {
+		close(lc->fd);
+		DBG(CXT, ul_debugobj(lc, "closing old open fd"));
+	}
+	lc->fd = -1;
+	lc->mode = 0;
+	lc->blocksize = 0;
+	lc->has_info = 0;
+	lc->info_failed = 0;
+	*lc->device = '\0';
+	memset(&lc->config, 0, sizeof(lc->config));
+
+	/* set new */
+	if (device) {
+		if (*device != '/') {
+			const char *dir = _PATH_DEV;
+
+			/* compose device name for /dev/loop<n> or /dev/loop/<n> */
+			if (lc->flags & LOOPDEV_FL_DEVSUBDIR) {
+				if (strlen(device) < 5)
+					return -1;
+				device += 4;
+				dir = _PATH_DEV_LOOP "/";	/* _PATH_DEV uses tailing slash */
+			}
+			snprintf(lc->device, sizeof(lc->device), "%s%s",
+				dir, device);
+		} else
+			xstrncpy(lc->device, device, sizeof(lc->device));
+
+		DBG(CXT, ul_debugobj(lc, "%s name assigned", device));
+	}
+
+	ul_unref_path(lc->sysfs);
+	lc->sysfs = NULL;
+	return 0;
+}
+
+int loopcxt_has_device(struct loopdev_cxt *lc)
+{
+	return lc && *lc->device;
+}
+
+/*
+ * @lc: context
+ * @flags: LOOPDEV_FL_* flags
+ *
+ * Initialize loop handler.
+ *
+ * We have two sets of the flags:
+ *
+ *	* LOOPDEV_FL_* flags control loopcxt_* API behavior
+ *
+ *	* LO_FLAGS_* are kernel flags used for LOOP_{SET,GET}_STAT64 ioctls
+ *
+ * Note about LOOPDEV_FL_{RDONLY,RDWR} flags. These flags are used for open(2)
+ * syscall to open loop device. By default is the device open read-only.
+ *
+ * The exception is loopcxt_setup_device(), where the device is open read-write
+ * if LO_FLAGS_READ_ONLY flags is not set (see loopcxt_set_flags()).
+ *
+ * Returns: <0 on error, 0 on success.
+ */
+int loopcxt_init(struct loopdev_cxt *lc, int flags)
+{
+	int rc;
+	struct stat st;
+	struct loopdev_cxt dummy = UL_LOOPDEVCXT_EMPTY;
+
+	if (!lc)
+		return -EINVAL;
+
+	loopdev_init_debug();
+	DBG(CXT, ul_debugobj(lc, "initialize context"));
+
+	memcpy(lc, &dummy, sizeof(dummy));
+	lc->flags = flags;
+
+	rc = loopcxt_set_device(lc, NULL);
+	if (rc)
+		return rc;
+
+	if (stat(_PATH_SYS_BLOCK, &st) || !S_ISDIR(st.st_mode)) {
+		lc->flags |= LOOPDEV_FL_NOSYSFS;
+		lc->flags &= ~LOOPDEV_FL_NOIOCTL;
+		DBG(CXT, ul_debugobj(lc, "init: disable /sys usage"));
+	}
+
+	if (!(lc->flags & LOOPDEV_FL_NOSYSFS) &&
+	    get_linux_version() >= KERNEL_VERSION(2,6,37)) {
+		/*
+		 * Use only sysfs for basic information about loop devices
+		 */
+		lc->flags |= LOOPDEV_FL_NOIOCTL;
+		DBG(CXT, ul_debugobj(lc, "init: ignore ioctls"));
+	}
+
+	if (!(lc->flags & LOOPDEV_FL_CONTROL) && !stat(_PATH_DEV_LOOPCTL, &st)) {
+		lc->flags |= LOOPDEV_FL_CONTROL;
+		DBG(CXT, ul_debugobj(lc, "init: loop-control detected "));
+	}
+
+	return 0;
+}
+
+/*
+ * @lc: context
+ *
+ * Deinitialize loop context
+ */
+void loopcxt_deinit(struct loopdev_cxt *lc)
+{
+	int errsv = errno;
+
+	if (!lc)
+		return;
+
+	DBG(CXT, ul_debugobj(lc, "de-initialize"));
+
+	free(lc->filename);
+	lc->filename = NULL;
+
+	ignore_result( loopcxt_set_device(lc, NULL) );
+	loopcxt_deinit_iterator(lc);
+
+	errno = errsv;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns newly allocated device path.
+ */
+char *loopcxt_strdup_device(struct loopdev_cxt *lc)
+{
+	if (!lc || !*lc->device)
+		return NULL;
+	return strdup(lc->device);
+}
+
+/*
+ * @lc: context
+ *
+ * Returns pointer device name in the @lc struct.
+ */
+const char *loopcxt_get_device(struct loopdev_cxt *lc)
+{
+	return lc && *lc->device ? lc->device : NULL;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns pointer to the sysfs context (see lib/sysfs.c)
+ */
+static struct path_cxt *loopcxt_get_sysfs(struct loopdev_cxt *lc)
+{
+	if (!lc || !*lc->device || (lc->flags & LOOPDEV_FL_NOSYSFS))
+		return NULL;
+
+	if (!lc->sysfs) {
+		dev_t devno = sysfs_devname_to_devno(lc->device);
+		if (!devno) {
+			DBG(CXT, ul_debugobj(lc, "sysfs: failed devname to devno"));
+			return NULL;
+		}
+
+		lc->sysfs = ul_new_sysfs_path(devno, NULL, NULL);
+		if (!lc->sysfs)
+			DBG(CXT, ul_debugobj(lc, "sysfs: init failed"));
+	}
+
+	return lc->sysfs;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns: file descriptor to the open loop device or <0 on error. The mode
+ *          depends on LOOPDEV_FL_{RDWR,RDONLY} context flags. Default is
+ *          read-only.
+ */
+int loopcxt_get_fd(struct loopdev_cxt *lc)
+{
+	if (!lc || !*lc->device)
+		return -EINVAL;
+
+	if (lc->fd < 0) {
+		lc->mode = lc->flags & LOOPDEV_FL_RDWR ? O_RDWR : O_RDONLY;
+		lc->fd = open(lc->device, lc->mode | O_CLOEXEC);
+		DBG(CXT, ul_debugobj(lc, "open %s [%s]: %m", lc->device,
+				lc->flags & LOOPDEV_FL_RDWR ? "rw" : "ro"));
+	}
+	return lc->fd;
+}
+
+int loopcxt_set_fd(struct loopdev_cxt *lc, int fd, int mode)
+{
+	if (!lc)
+		return -EINVAL;
+
+	lc->fd = fd;
+	lc->mode = mode;
+	return 0;
+}
+
+/*
+ * @lc: context
+ * @flags: LOOPITER_FL_* flags
+ *
+ * Iterator can be used to scan list of the free or used loop devices.
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_init_iterator(struct loopdev_cxt *lc, int flags)
+{
+	struct loopdev_iter *iter;
+	struct stat st;
+
+	if (!lc)
+		return -EINVAL;
+
+
+	iter = &lc->iter;
+	DBG(ITER, ul_debugobj(iter, "initialize"));
+
+	/* always zeroize
+	 */
+	memset(iter, 0, sizeof(*iter));
+	iter->ncur = -1;
+	iter->flags = flags;
+	iter->default_check = 1;
+
+	if (!lc->extra_check) {
+		/*
+		 * Check for /dev/loop/<N> subdirectory
+		 */
+		if (!(lc->flags & LOOPDEV_FL_DEVSUBDIR) &&
+		    stat(_PATH_DEV_LOOP, &st) == 0 && S_ISDIR(st.st_mode))
+			lc->flags |= LOOPDEV_FL_DEVSUBDIR;
+
+		lc->extra_check = 1;
+	}
+	return 0;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_deinit_iterator(struct loopdev_cxt *lc)
+{
+	struct loopdev_iter *iter;
+
+	if (!lc)
+		return -EINVAL;
+
+	iter = &lc->iter;
+	DBG(ITER, ul_debugobj(iter, "de-initialize"));
+
+	free(iter->minors);
+	if (iter->proc)
+		fclose(iter->proc);
+	if (iter->sysblock)
+		closedir(iter->sysblock);
+
+	memset(iter, 0, sizeof(*iter));
+	return 0;
+}
+
+/*
+ * Same as loopcxt_set_device, but also checks if the device is
+ * associated with any file.
+ *
+ * Returns: <0 on error, 0 on success, 1 device does not match with
+ *         LOOPITER_FL_{USED,FREE} flags.
+ */
+static int loopiter_set_device(struct loopdev_cxt *lc, const char *device)
+{
+	int rc = loopcxt_set_device(lc, device);
+	int used;
+
+	if (rc)
+		return rc;
+
+	if (!(lc->iter.flags & LOOPITER_FL_USED) &&
+	    !(lc->iter.flags & LOOPITER_FL_FREE))
+		return 0;	/* caller does not care about device status */
+
+	if (!is_loopdev(lc->device)) {
+		DBG(ITER, ul_debugobj(&lc->iter, "%s does not exist", lc->device));
+		return -errno;
+	}
+
+	DBG(ITER, ul_debugobj(&lc->iter, "%s exist", lc->device));
+
+	used = loopcxt_get_offset(lc, NULL) == 0;
+
+	if ((lc->iter.flags & LOOPITER_FL_USED) && used)
+		return 0;
+
+	if ((lc->iter.flags & LOOPITER_FL_FREE) && !used)
+		return 0;
+
+	DBG(ITER, ul_debugobj(&lc->iter, "failed to use %s device", lc->device));
+
+	ignore_result( loopcxt_set_device(lc, NULL) );
+	return 1;
+}
+
+static int cmpnum(const void *p1, const void *p2)
+{
+	return (((* (const int *) p1) > (* (const int *) p2)) -
+			((* (const int *) p1) < (* (const int *) p2)));
+}
+
+/*
+ * The classic scandir() is more expensive and less portable.
+ * We needn't full loop device names -- loop numbers (loop<N>)
+ * are enough.
+ */
+static int loop_scandir(const char *dirname, int **ary, int hasprefix)
+{
+	DIR *dir;
+	struct dirent *d;
+	unsigned int n, count = 0, arylen = 0;
+
+	if (!dirname || !ary)
+		return 0;
+
+	DBG(ITER, ul_debug("scan dir: %s", dirname));
+
+	dir = opendir(dirname);
+	if (!dir)
+		return 0;
+	free(*ary);
+	*ary = NULL;
+
+	while((d = readdir(dir))) {
+#ifdef _DIRENT_HAVE_D_TYPE
+		if (d->d_type != DT_BLK && d->d_type != DT_UNKNOWN &&
+		    d->d_type != DT_LNK)
+			continue;
+#endif
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+
+		if (hasprefix) {
+			/* /dev/loop<N> */
+			if (sscanf(d->d_name, "loop%u", &n) != 1)
+				continue;
+		} else {
+			/* /dev/loop/<N> */
+			char *end = NULL;
+
+			errno = 0;
+			n = strtol(d->d_name, &end, 10);
+			if (d->d_name == end || (end && *end) || errno)
+				continue;
+		}
+		if (n < LOOPDEV_DEFAULT_NNODES)
+			continue;			/* ignore loop<0..7> */
+
+		if (count + 1 > arylen) {
+			int *tmp;
+
+			arylen += 1;
+
+			tmp = realloc(*ary, arylen * sizeof(int));
+			if (!tmp) {
+				free(*ary);
+				*ary = NULL;
+				closedir(dir);
+				return -1;
+			}
+			*ary = tmp;
+		}
+		if (*ary)
+			(*ary)[count++] = n;
+	}
+	if (count && *ary)
+		qsort(*ary, count, sizeof(int), cmpnum);
+
+	closedir(dir);
+	return count;
+}
+
+/*
+ * Set the next *used* loop device according to /proc/partitions.
+ *
+ * Loop devices smaller than 512 bytes are invisible for this function.
+ */
+static int loopcxt_next_from_proc(struct loopdev_cxt *lc)
+{
+	struct loopdev_iter *iter = &lc->iter;
+	char buf[BUFSIZ];
+
+	DBG(ITER, ul_debugobj(iter, "scan /proc/partitions"));
+
+	if (!iter->proc)
+		iter->proc = fopen(_PATH_PROC_PARTITIONS, "r" UL_CLOEXECSTR);
+	if (!iter->proc)
+		return 1;
+
+	while (fgets(buf, sizeof(buf), iter->proc)) {
+		unsigned int m;
+		char name[128 + 1];
+
+
+		if (sscanf(buf, " %u %*s %*s %128[^\n ]",
+			   &m, name) != 2 || m != LOOPDEV_MAJOR)
+			continue;
+
+		DBG(ITER, ul_debugobj(iter, "checking %s", name));
+
+		if (loopiter_set_device(lc, name) == 0)
+			return 0;
+	}
+
+	return 1;
+}
+
+/*
+ * Set the next *used* loop device according to
+ * /sys/block/loopN/loop/backing_file (kernel >= 2.6.37 is required).
+ *
+ * This is preferred method.
+ */
+static int loopcxt_next_from_sysfs(struct loopdev_cxt *lc)
+{
+	struct loopdev_iter *iter = &lc->iter;
+	struct dirent *d;
+	int fd;
+
+	DBG(ITER, ul_debugobj(iter, "scanning /sys/block"));
+
+	if (!iter->sysblock)
+		iter->sysblock = opendir(_PATH_SYS_BLOCK);
+
+	if (!iter->sysblock)
+		return 1;
+
+	fd = dirfd(iter->sysblock);
+
+	while ((d = readdir(iter->sysblock))) {
+		char name[NAME_MAX + 18 + 1];
+		struct stat st;
+
+		DBG(ITER, ul_debugobj(iter, "check %s", d->d_name));
+
+		if (strcmp(d->d_name, ".") == 0
+		    || strcmp(d->d_name, "..") == 0
+		    || strncmp(d->d_name, "loop", 4) != 0)
+			continue;
+
+		snprintf(name, sizeof(name), "%s/loop/backing_file", d->d_name);
+		if (fstatat(fd, name, &st, 0) != 0)
+			continue;
+
+		if (loopiter_set_device(lc, d->d_name) == 0)
+			return 0;
+	}
+
+	return 1;
+}
+
+/*
+ * @lc: context, has to initialized by loopcxt_init_iterator()
+ *
+ * Returns: 0 on success, < 0 on error, 1 at the end of scanning. The details
+ *          about the current loop device are available by
+ *          loopcxt_get_{fd,backing_file,device,offset, ...} functions.
+ */
+int loopcxt_next(struct loopdev_cxt *lc)
+{
+	struct loopdev_iter *iter;
+
+	if (!lc)
+		return -EINVAL;
+
+
+	iter = &lc->iter;
+	if (iter->done)
+		return 1;
+
+	DBG(ITER, ul_debugobj(iter, "next"));
+
+	/* A) Look for used loop devices in /proc/partitions ("losetup -a" only)
+	 */
+	if (iter->flags & LOOPITER_FL_USED) {
+		int rc;
+
+		if (loopcxt_sysfs_available(lc))
+			rc = loopcxt_next_from_sysfs(lc);
+		else
+			rc = loopcxt_next_from_proc(lc);
+		if (rc == 0)
+			return 0;
+		goto done;
+	}
+
+	/* B) Classic way, try first eight loop devices (default number
+	 *    of loop devices). This is enough for 99% of all cases.
+	 */
+	if (iter->default_check) {
+		DBG(ITER, ul_debugobj(iter, "next: default check"));
+		for (++iter->ncur; iter->ncur < LOOPDEV_DEFAULT_NNODES;
+							iter->ncur++) {
+			char name[16];
+			snprintf(name, sizeof(name), "loop%d", iter->ncur);
+
+			if (loopiter_set_device(lc, name) == 0)
+				return 0;
+		}
+		iter->default_check = 0;
+	}
+
+	/* C) the worst possibility, scan whole /dev or /dev/loop/<N>
+	 */
+	if (!iter->minors) {
+		DBG(ITER, ul_debugobj(iter, "next: scanning /dev"));
+		iter->nminors = (lc->flags & LOOPDEV_FL_DEVSUBDIR) ?
+			loop_scandir(_PATH_DEV_LOOP, &iter->minors, 0) :
+			loop_scandir(_PATH_DEV, &iter->minors, 1);
+		iter->ncur = -1;
+	}
+	for (++iter->ncur; iter->ncur < iter->nminors; iter->ncur++) {
+		char name[16];
+		snprintf(name, sizeof(name), "loop%d", iter->minors[iter->ncur]);
+
+		if (loopiter_set_device(lc, name) == 0)
+			return 0;
+	}
+done:
+	loopcxt_deinit_iterator(lc);
+	return 1;
+}
+
+/*
+ * @device: path to device
+ */
+int is_loopdev(const char *device)
+{
+	struct stat st;
+	int rc = 0;
+
+	if (!device || stat(device, &st) != 0 || !S_ISBLK(st.st_mode))
+		rc = 0;
+	else if (major(st.st_rdev) == LOOPDEV_MAJOR)
+		rc = 1;
+	else if (sysfs_devno_is_wholedisk(st.st_rdev)) {
+		/* It's possible that kernel creates a device with a different
+		 * major number ... check by /sys it's really loop device.
+		 */
+		char name[PATH_MAX], *cn, *p = NULL;
+
+		snprintf(name, sizeof(name), _PATH_SYS_DEVBLOCK "/%d:%d",
+				major(st.st_rdev), minor(st.st_rdev));
+		cn = canonicalize_path(name);
+		if (cn)
+			p = stripoff_last_component(cn);
+		rc = p && startswith(p, "loop");
+		free(cn);
+	}
+
+	if (rc == 0)
+		errno = ENODEV;
+	return rc;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns result from LOOP_GET_STAT64 ioctl or NULL on error.
+ */
+struct loop_info64 *loopcxt_get_info(struct loopdev_cxt *lc)
+{
+	int fd;
+
+	if (!lc || lc->info_failed) {
+		errno = EINVAL;
+		return NULL;
+	}
+	errno = 0;
+	if (lc->has_info)
+		return &lc->config.info;
+
+	fd = loopcxt_get_fd(lc);
+	if (fd < 0)
+		return NULL;
+
+	if (ioctl(fd, LOOP_GET_STATUS64, &lc->config.info) == 0) {
+		lc->has_info = 1;
+		lc->info_failed = 0;
+		DBG(CXT, ul_debugobj(lc, "reading loop_info64 OK"));
+		return &lc->config.info;
+	}
+
+	lc->info_failed = 1;
+	DBG(CXT, ul_debugobj(lc, "reading loop_info64 FAILED"));
+
+	return NULL;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns (allocated) string with path to the file associated
+ * with the current loop device.
+ */
+char *loopcxt_get_backing_file(struct loopdev_cxt *lc)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+	char *res = NULL;
+
+	if (sysfs)
+		/*
+		 * This is always preferred, the loop_info64
+		 * has too small buffer for the filename.
+		 */
+		ul_path_read_string(sysfs, &res, "loop/backing_file");
+
+	if (!res && loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+
+		if (lo) {
+			lo->lo_file_name[LO_NAME_SIZE - 2] = '*';
+			lo->lo_file_name[LO_NAME_SIZE - 1] = '\0';
+			res = strdup((char *) lo->lo_file_name);
+		}
+	}
+
+	DBG(CXT, ul_debugobj(lc, "get_backing_file [%s]", res));
+	return res;
+}
+
+/*
+ * @lc: context
+ * @offset: returns offset number for the given device
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_get_offset(struct loopdev_cxt *lc, uint64_t *offset)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+	int rc = -EINVAL;
+
+	if (sysfs)
+		if (ul_path_read_u64(sysfs, offset, "loop/offset") == 0)
+			rc = 0;
+
+	if (rc && loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+		if (lo) {
+			if (offset)
+				*offset = lo->lo_offset;
+			rc = 0;
+		} else
+			rc = -errno;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "get_offset [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * @lc: context
+ * @blocksize: returns logical blocksize for the given device
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_get_blocksize(struct loopdev_cxt *lc, uint64_t *blocksize)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+	int rc = -EINVAL;
+
+	if (sysfs)
+		if (ul_path_read_u64(sysfs, blocksize, "queue/logical_block_size") == 0)
+			rc = 0;
+
+	/* Fallback based on BLKSSZGET ioctl */
+	if (rc) {
+		int fd = loopcxt_get_fd(lc);
+		int sz = 0;
+
+		if (fd < 0)
+			return -EINVAL;
+		rc = blkdev_get_sector_size(fd, &sz);
+		if (rc)
+			return rc;
+
+		*blocksize = sz;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "get_blocksize [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * @lc: context
+ * @sizelimit: returns size limit for the given device
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_get_sizelimit(struct loopdev_cxt *lc, uint64_t *size)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+	int rc = -EINVAL;
+
+	if (sysfs)
+		if (ul_path_read_u64(sysfs, size, "loop/sizelimit") == 0)
+			rc = 0;
+
+	if (rc && loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+		if (lo) {
+			if (size)
+				*size = lo->lo_sizelimit;
+			rc = 0;
+		} else
+			rc = -errno;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "get_sizelimit [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * @lc: context
+ * @devno: returns encryption type
+ *
+ * Cryptoloop is DEPRECATED!
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_get_encrypt_type(struct loopdev_cxt *lc, uint32_t *type)
+{
+	struct loop_info64 *lo = loopcxt_get_info(lc);
+	int rc;
+
+	/* not provided by sysfs */
+	if (lo) {
+		if (type)
+			*type = lo->lo_encrypt_type;
+		rc = 0;
+	} else
+		rc = -errno;
+
+	DBG(CXT, ul_debugobj(lc, "get_encrypt_type [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * @lc: context
+ * @devno: returns crypt name
+ *
+ * Cryptoloop is DEPRECATED!
+ *
+ * Returns: <0 on error, 0 on success
+ */
+const char *loopcxt_get_crypt_name(struct loopdev_cxt *lc)
+{
+	struct loop_info64 *lo = loopcxt_get_info(lc);
+
+	if (lo)
+		return (char *) lo->lo_crypt_name;
+
+	DBG(CXT, ul_debugobj(lc, "get_crypt_name failed"));
+	return NULL;
+}
+
+/*
+ * @lc: context
+ * @devno: returns backing file devno
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_get_backing_devno(struct loopdev_cxt *lc, dev_t *devno)
+{
+	struct loop_info64 *lo = loopcxt_get_info(lc);
+	int rc;
+
+	if (lo) {
+		if (devno)
+			*devno = lo->lo_device;
+		rc = 0;
+	} else
+		rc = -errno;
+
+	DBG(CXT, ul_debugobj(lc, "get_backing_devno [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * @lc: context
+ * @ino: returns backing file inode
+ *
+ * Returns: <0 on error, 0 on success
+ */
+int loopcxt_get_backing_inode(struct loopdev_cxt *lc, ino_t *ino)
+{
+	struct loop_info64 *lo = loopcxt_get_info(lc);
+	int rc;
+
+	if (lo) {
+		if (ino)
+			*ino = lo->lo_inode;
+		rc = 0;
+	} else
+		rc = -errno;
+
+	DBG(CXT, ul_debugobj(lc, "get_backing_inode [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * Check if the kernel supports partitioned loop devices.
+ *
+ * Notes:
+ *   - kernels < 3.2 support partitioned loop devices and PT scanning
+ *     only if max_part= module parameter is non-zero
+ *
+ *   - kernels >= 3.2 always support partitioned loop devices
+ *
+ *   - kernels >= 3.2 always support BLKPG_{ADD,DEL}_PARTITION ioctls
+ *
+ *   - kernels >= 3.2 enable PT scanner only if max_part= is non-zero or if the
+ *     LO_FLAGS_PARTSCAN flag is set for the device. The PT scanner is disabled
+ *     by default.
+ *
+ *  See kernel commit e03c8dd14915fabc101aa495828d58598dc5af98.
+ */
+int loopmod_supports_partscan(void)
+{
+	int rc, ret = 0;
+	FILE *f;
+
+	if (get_linux_version() >= KERNEL_VERSION(3,2,0))
+		return 1;
+
+	f = fopen("/sys/module/loop/parameters/max_part", "r" UL_CLOEXECSTR);
+	if (!f)
+		return 0;
+	rc = fscanf(f, "%d", &ret);
+	fclose(f);
+	return rc == 1 ? ret : 0;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns: 1 if the partscan flags is set *or* (for old kernels) partitions
+ * scanning is enabled for all loop devices.
+ */
+int loopcxt_is_partscan(struct loopdev_cxt *lc)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+
+	if (sysfs) {
+		/* kernel >= 3.2 */
+		int fl;
+		if (ul_path_read_s32(sysfs, &fl, "loop/partscan") == 0)
+			return fl;
+	}
+
+	/* old kernels (including kernels without loopN/loop/<flags> directory */
+	return loopmod_supports_partscan();
+}
+
+/*
+ * @lc: context
+ *
+ * Returns: 1 if the autoclear flags is set.
+ */
+int loopcxt_is_autoclear(struct loopdev_cxt *lc)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+
+	if (sysfs) {
+		int fl;
+		if (ul_path_read_s32(sysfs, &fl, "loop/autoclear") == 0)
+			return fl;
+	}
+
+	if (loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+		if (lo)
+			return lo->lo_flags & LO_FLAGS_AUTOCLEAR;
+	}
+	return 0;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns: 1 if the readonly flags is set.
+ */
+int loopcxt_is_readonly(struct loopdev_cxt *lc)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+
+	if (sysfs) {
+		int fl;
+		if (ul_path_read_s32(sysfs, &fl, "ro") == 0)
+			return fl;
+	}
+
+	if (loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+		if (lo)
+			return lo->lo_flags & LO_FLAGS_READ_ONLY;
+	}
+	return 0;
+}
+
+/*
+ * @lc: context
+ *
+ * Returns: 1 if the dio flags is set.
+ */
+int loopcxt_is_dio(struct loopdev_cxt *lc)
+{
+	struct path_cxt *sysfs = loopcxt_get_sysfs(lc);
+
+	if (sysfs) {
+		int fl;
+		if (ul_path_read_s32(sysfs, &fl, "loop/dio") == 0)
+			return fl;
+	}
+	if (loopcxt_ioctl_enabled(lc)) {
+		struct loop_info64 *lo = loopcxt_get_info(lc);
+		if (lo)
+			return lo->lo_flags & LO_FLAGS_DIRECT_IO;
+	}
+	return 0;
+}
+
+/*
+ * @lc: context
+ * @st: backing file stat or NULL
+ * @backing_file: filename
+ * @offset: offset (use LOOPDEV_FL_OFFSET if specified)
+ * @sizelimit: size limit (use LOOPDEV_FL_SIZELIMIT if specified)
+ * @flags: LOOPDEV_FL_{OFFSET,SIZELIMIT}
+ *
+ * Returns 1 if the current @lc loopdev is associated with the given backing
+ * file. Note that the preferred way is to use devno and inode number rather
+ * than filename. The @backing_file filename is poor solution usable in case
+ * that you don't have rights to call stat().
+ *
+ * LOOPDEV_FL_SIZELIMIT requires LOOPDEV_FL_OFFSET being set as well.
+ *
+ * Don't forget that old kernels provide very restricted (in size) backing
+ * filename by LOOP_GET_STAT64 ioctl only.
+ */
+int loopcxt_is_used(struct loopdev_cxt *lc,
+		    struct stat *st,
+		    const char *backing_file,
+		    uint64_t offset,
+		    uint64_t sizelimit,
+		    int flags)
+{
+	ino_t ino = 0;
+	dev_t dev = 0;
+
+	if (!lc)
+		return 0;
+
+	DBG(CXT, ul_debugobj(lc, "checking %s vs. %s",
+				loopcxt_get_device(lc),
+				backing_file));
+
+	if (st && loopcxt_get_backing_inode(lc, &ino) == 0 &&
+		  loopcxt_get_backing_devno(lc, &dev) == 0) {
+
+		if (ino == st->st_ino && dev == st->st_dev)
+			goto found;
+
+		/* don't use filename if we have devno and inode */
+		return 0;
+	}
+
+	/* poor man's solution */
+	if (backing_file) {
+		char *name = loopcxt_get_backing_file(lc);
+		int rc = name && strcmp(name, backing_file) == 0;
+
+		free(name);
+		if (rc)
+			goto found;
+	}
+
+	return 0;
+found:
+	if (flags & LOOPDEV_FL_OFFSET) {
+		uint64_t off = 0;
+
+		int rc = loopcxt_get_offset(lc, &off) == 0 && off == offset;
+
+		if (rc && flags & LOOPDEV_FL_SIZELIMIT) {
+			uint64_t sz = 0;
+
+			return loopcxt_get_sizelimit(lc, &sz) == 0 && sz == sizelimit;
+		}
+		return rc;
+	}
+	return 1;
+}
+
+/*
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ */
+int loopcxt_set_offset(struct loopdev_cxt *lc, uint64_t offset)
+{
+	if (!lc)
+		return -EINVAL;
+	lc->config.info.lo_offset = offset;
+
+	DBG(CXT, ul_debugobj(lc, "set offset=%jd", offset));
+	return 0;
+}
+
+/*
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ */
+int loopcxt_set_sizelimit(struct loopdev_cxt *lc, uint64_t sizelimit)
+{
+	if (!lc)
+		return -EINVAL;
+	lc->config.info.lo_sizelimit = sizelimit;
+
+	DBG(CXT, ul_debugobj(lc, "set sizelimit=%jd", sizelimit));
+	return 0;
+}
+
+/*
+ * The blocksize will be used by loopcxt_set_device(). For already exiting
+ * devices use  loopcxt_ioctl_blocksize().
+ *
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ */
+int loopcxt_set_blocksize(struct loopdev_cxt *lc, uint64_t blocksize)
+{
+	if (!lc)
+		return -EINVAL;
+	lc->blocksize = blocksize;
+
+	DBG(CXT, ul_debugobj(lc, "set blocksize=%jd", blocksize));
+	return 0;
+}
+
+/*
+ * @lc: context
+ * @flags: kernel LO_FLAGS_{READ_ONLY,USE_AOPS,AUTOCLEAR} flags
+ *
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ *
+ * Returns: 0 on success, <0 on error.
+ */
+int loopcxt_set_flags(struct loopdev_cxt *lc, uint32_t flags)
+{
+	if (!lc)
+		return -EINVAL;
+	lc->config.info.lo_flags = flags;
+
+	DBG(CXT, ul_debugobj(lc, "set flags=%u", (unsigned) flags));
+	return 0;
+}
+
+/*
+ * @lc: context
+ * @filename: backing file path (the path will be canonicalized)
+ *
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ *
+ * Returns: 0 on success, <0 on error.
+ */
+int loopcxt_set_backing_file(struct loopdev_cxt *lc, const char *filename)
+{
+	if (!lc)
+		return -EINVAL;
+
+	lc->filename = canonicalize_path(filename);
+	if (!lc->filename)
+		return -errno;
+
+	xstrncpy((char *)lc->config.info.lo_file_name, lc->filename, LO_NAME_SIZE);
+
+	DBG(CXT, ul_debugobj(lc, "set backing file=%s", lc->config.info.lo_file_name));
+	return 0;
+}
+
+/*
+ * In kernels prior to v3.9, if the offset or sizelimit options
+ * are used, the block device's size won't be synced automatically.
+ * blockdev --getsize64 and filesystems will use the backing
+ * file size until the block device has been re-opened or the
+ * LOOP_SET_CAPACITY ioctl is called to sync the sizes.
+ *
+ * Since mount -oloop uses the LO_FLAGS_AUTOCLEAR option and passes
+ * the open file descriptor to the mount system call, we need to use
+ * the ioctl. Calling losetup directly doesn't have this problem since
+ * it closes the device when it exits and whatever consumes the device
+ * next will re-open it, causing the resync.
+ */
+static int loopcxt_check_size(struct loopdev_cxt *lc, int file_fd)
+{
+	uint64_t size, expected_size;
+	int dev_fd;
+	struct stat st;
+
+	if (!lc->config.info.lo_offset && !lc->config.info.lo_sizelimit)
+		return 0;
+
+	if (fstat(file_fd, &st)) {
+		DBG(CXT, ul_debugobj(lc, "failed to fstat backing file"));
+		return -errno;
+	}
+	if (S_ISBLK(st.st_mode)) {
+		if (blkdev_get_size(file_fd,
+				(unsigned long long *) &expected_size)) {
+			DBG(CXT, ul_debugobj(lc, "failed to determine device size"));
+			return -errno;
+		}
+	} else
+		expected_size = st.st_size;
+
+	if (expected_size == 0 || expected_size <= lc->config.info.lo_offset) {
+		DBG(CXT, ul_debugobj(lc, "failed to determine expected size"));
+		return 0;	/* ignore this error */
+	}
+
+	if (lc->config.info.lo_offset > 0)
+		expected_size -= lc->config.info.lo_offset;
+
+	if (lc->config.info.lo_sizelimit > 0 && lc->config.info.lo_sizelimit < expected_size)
+		expected_size = lc->config.info.lo_sizelimit;
+
+	dev_fd = loopcxt_get_fd(lc);
+	if (dev_fd < 0) {
+		DBG(CXT, ul_debugobj(lc, "failed to get loop FD"));
+		return -errno;
+	}
+
+	if (blkdev_get_size(dev_fd, (unsigned long long *) &size)) {
+		DBG(CXT, ul_debugobj(lc, "failed to determine loopdev size"));
+		return -errno;
+	}
+
+	/* It's block device, so, align to 512-byte sectors */
+	if (expected_size % 512) {
+		DBG(CXT, ul_debugobj(lc, "expected size misaligned to 512-byte sectors"));
+		expected_size = (expected_size >> 9) << 9;
+	}
+
+	if (expected_size != size) {
+		DBG(CXT, ul_debugobj(lc, "warning: loopdev and expected "
+				      "size mismatch (%ju/%ju)",
+				      size, expected_size));
+
+		if (loopcxt_ioctl_capacity(lc)) {
+			/* ioctl not available */
+			if (errno == ENOTTY || errno == EINVAL)
+				errno = ERANGE;
+			return -errno;
+		}
+
+		if (blkdev_get_size(dev_fd, (unsigned long long *) &size))
+			return -errno;
+
+		if (expected_size != size) {
+			errno = ERANGE;
+			DBG(CXT, ul_debugobj(lc, "failed to set loopdev size, "
+					"size: %ju, expected: %ju",
+					size, expected_size));
+			return -errno;
+		}
+	}
+
+	return 0;
+}
+
+
+/*
+ * @lc: context
+ *
+ * Associate the current device (see loopcxt_{set,get}_device()) with
+ * a file (see loopcxt_set_backing_file()).
+ *
+ * The device is initialized read-write by default. If you want read-only
+ * device then set LO_FLAGS_READ_ONLY by loopcxt_set_flags(). The LOOPDEV_FL_*
+ * flags are ignored and modified according to LO_FLAGS_*.
+ *
+ * If the device is already open by loopcxt_get_fd() then this setup device
+ * function will re-open the device to fix read/write mode.
+ *
+ * The device is also initialized read-only if the backing file is not
+ * possible to open read-write (e.g. read-only FS).
+ *
+ * Returns: <0 on error, 0 on success.
+ */
+int loopcxt_setup_device(struct loopdev_cxt *lc)
+{
+	int file_fd, dev_fd, mode = O_RDWR, flags = O_CLOEXEC;
+	int rc = -1, cnt = 0;
+	int errsv = 0;
+	int fallback = 0;
+
+	if (!lc || !*lc->device || !lc->filename)
+		return -EINVAL;
+
+	DBG(SETUP, ul_debugobj(lc, "device setup requested"));
+
+	/*
+	 * Open backing file and device
+	 */
+	if (lc->config.info.lo_flags & LO_FLAGS_READ_ONLY)
+		mode = O_RDONLY;
+
+	if (lc->config.info.lo_flags & LO_FLAGS_DIRECT_IO)
+		flags |= O_DIRECT;
+
+	if ((file_fd = open(lc->filename, mode | flags)) < 0) {
+		if (mode != O_RDONLY && (errno == EROFS || errno == EACCES))
+			file_fd = open(lc->filename, (mode = O_RDONLY) | flags);
+
+		if (file_fd < 0) {
+			DBG(SETUP, ul_debugobj(lc, "open backing file failed: %m"));
+			return -errno;
+		}
+	}
+	DBG(SETUP, ul_debugobj(lc, "backing file open: OK"));
+
+	if (lc->fd != -1 && lc->mode != mode) {
+		DBG(SETUP, ul_debugobj(lc, "closing already open device (mode mismatch)"));
+		close(lc->fd);
+		lc->fd = -1;
+		lc->mode = 0;
+	}
+
+	if (mode == O_RDONLY) {
+		lc->flags |= LOOPDEV_FL_RDONLY;			/* open() mode */
+		lc->config.info.lo_flags |= LO_FLAGS_READ_ONLY;	/* kernel loopdev mode */
+	} else {
+		lc->flags |= LOOPDEV_FL_RDWR;			/* open() mode */
+		lc->config.info.lo_flags &= ~LO_FLAGS_READ_ONLY;
+		lc->flags &= ~LOOPDEV_FL_RDONLY;
+	}
+
+	do {
+		errno = 0;
+		dev_fd = loopcxt_get_fd(lc);
+		if (dev_fd >= 0 || lc->control_ok == 0)
+			break;
+		if (errno != EACCES && errno != ENOENT)
+			break;
+		/* We have permissions to open /dev/loop-control, but open
+		 * /dev/loopN failed with EACCES, it's probably because udevd
+		 * does not applied chown yet. Let's wait a moment. */
+		xusleep(25000);
+	} while (cnt++ < 16);
+
+	if (dev_fd < 0) {
+		rc = -errno;
+		goto err;
+	}
+
+	DBG(SETUP, ul_debugobj(lc, "device open: OK"));
+
+	/*
+	 * Atomic way to configure all by one ioctl call
+	 * -- since Linux v5.8-rc1, commit 3448914e8cc550ba792d4ccc74471d1ca4293aae
+	 */
+	lc->config.fd = file_fd;
+	if (lc->blocksize > 0)
+		lc->config.block_size = lc->blocksize;
+
+	rc = repeat_on_eagain( ioctl(dev_fd, LOOP_CONFIGURE, &lc->config) );
+	if (rc != 0) {
+		errsv = errno;
+		if (errno != EINVAL && errno != ENOTTY && errno != ENOSYS) {
+			DBG(SETUP, ul_debugobj(lc, "LOOP_CONFIGURE failed: %m"));
+			goto err;
+		}
+		fallback = 1;
+	} else {
+		DBG(SETUP, ul_debugobj(lc, "LOOP_CONFIGURE: OK"));
+	}
+
+	/*
+	 * Old deprecated way; first assign backing file FD and then in the
+	 * second step set loop device properties.
+	 */
+	if (fallback) {
+		if (ioctl(dev_fd, LOOP_SET_FD, file_fd) < 0) {
+			rc = -errno;
+			errsv = errno;
+			DBG(SETUP, ul_debugobj(lc, "LOOP_SET_FD failed: %m"));
+			goto err;
+		}
+
+		DBG(SETUP, ul_debugobj(lc, "LOOP_SET_FD: OK"));
+
+		if (lc->blocksize > 0
+			&& (rc = loopcxt_ioctl_blocksize(lc, lc->blocksize)) < 0) {
+			errsv = -rc;
+			goto err;
+		}
+
+		if ((rc = loopcxt_ioctl_status(lc)) < 0) {
+			errsv = -rc;
+			goto err;
+		}
+	}
+
+	if ((rc = loopcxt_check_size(lc, file_fd)))
+		goto err;
+
+	close(file_fd);
+
+	memset(&lc->config, 0, sizeof(lc->config));
+	lc->has_info = 0;
+	lc->info_failed = 0;
+
+	DBG(SETUP, ul_debugobj(lc, "success [rc=0]"));
+	return 0;
+err:
+	if (file_fd >= 0)
+		close(file_fd);
+	if (dev_fd >= 0 && rc != -EBUSY)
+		ioctl(dev_fd, LOOP_CLR_FD, 0);
+	if (errsv)
+		errno = errsv;
+
+	DBG(SETUP, ul_debugobj(lc, "failed [rc=%d]", rc));
+	return rc;
+}
+
+
+/*
+ * @lc: context
+ *
+ * Update status of the current device (see loopcxt_{set,get}_device()).
+ *
+ * Note that once initialized, kernel accepts only selected changes:
+ * LO_FLAGS_AUTOCLEAR and LO_FLAGS_PARTSCAN
+ * For more see linux/drivers/block/loop.c:loop_set_status()
+ *
+ * Returns: <0 on error, 0 on success.
+ */
+int loopcxt_ioctl_status(struct loopdev_cxt *lc)
+{
+	int dev_fd, rc;
+
+	errno = 0;
+	dev_fd = loopcxt_get_fd(lc);
+
+	if (dev_fd < 0)
+		return -errno;
+
+	DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_STATUS64"));
+
+	rc = repeat_on_eagain( ioctl(dev_fd, LOOP_SET_STATUS64, &lc->config.info) );
+	if (rc != 0) {
+		DBG(SETUP, ul_debugobj(lc, "LOOP_SET_STATUS64 failed: %m"));
+		return rc;
+	}
+
+	DBG(SETUP, ul_debugobj(lc, "LOOP_SET_STATUS64: OK"));
+	return 0;
+}
+
+int loopcxt_ioctl_capacity(struct loopdev_cxt *lc)
+{
+	int rc, fd = loopcxt_get_fd(lc);
+
+	if (fd < 0)
+		return -EINVAL;
+
+	DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_CAPACITY"));
+
+	/* Kernels prior to v2.6.30 don't support this ioctl */
+	rc = repeat_on_eagain( ioctl(fd, LOOP_SET_CAPACITY, 0) );
+	if (rc != 0) {
+		DBG(CXT, ul_debugobj(lc, "LOOP_SET_CAPACITY failed: %m"));
+		return rc;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "capacity set"));
+	return 0;
+}
+
+int loopcxt_ioctl_dio(struct loopdev_cxt *lc, unsigned long use_dio)
+{
+	int rc, fd = loopcxt_get_fd(lc);
+
+	if (fd < 0)
+		return -EINVAL;
+
+	DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_DIRECT_IO"));
+
+	/* Kernels prior to v4.4 don't support this ioctl */
+	rc = repeat_on_eagain( ioctl(fd, LOOP_SET_DIRECT_IO, use_dio) );
+	if (rc != 0) {
+		DBG(CXT, ul_debugobj(lc, "LOOP_SET_DIRECT_IO failed: %m"));
+		return rc;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "direct io set"));
+	return 0;
+}
+
+/*
+ * Kernel uses "unsigned long" as ioctl arg, but we use u64 for all sizes to
+ * keep loopdev internal API simple.
+ */
+int loopcxt_ioctl_blocksize(struct loopdev_cxt *lc, uint64_t blocksize)
+{
+	int rc, fd = loopcxt_get_fd(lc);
+
+	if (fd < 0)
+		return -EINVAL;
+
+	DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_BLOCK_SIZE"));
+
+	rc = repeat_on_eagain(
+		ioctl(fd, LOOP_SET_BLOCK_SIZE, (unsigned long) blocksize) );
+	if (rc != 0) {
+		DBG(CXT, ul_debugobj(lc, "LOOP_SET_BLOCK_SIZE failed: %m"));
+		return rc;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "logical block size set"));
+	return 0;
+}
+
+int loopcxt_delete_device(struct loopdev_cxt *lc)
+{
+	int rc, fd = loopcxt_get_fd(lc);
+
+	if (fd < 0)
+		return -EINVAL;
+
+	DBG(SETUP, ul_debugobj(lc, "calling LOOP_SET_CLR_FD"));
+
+	rc = repeat_on_eagain( ioctl(fd, LOOP_CLR_FD, 0) );
+	if (rc != 0) {
+		DBG(CXT, ul_debugobj(lc, "LOOP_CLR_FD failed: %m"));
+		return rc;
+	}
+
+	DBG(CXT, ul_debugobj(lc, "device removed"));
+	return 0;
+}
+
+int loopcxt_add_device(struct loopdev_cxt *lc)
+{
+	int rc = -EINVAL;
+	int ctl, nr = -1;
+	const char *p, *dev = loopcxt_get_device(lc);
+
+	if (!dev)
+		goto done;
+
+	if (!(lc->flags & LOOPDEV_FL_CONTROL)) {
+		rc = -ENOSYS;
+		goto done;
+	}
+
+	p = strrchr(dev, '/');
+	if (!p || (sscanf(p, "/loop%d", &nr) != 1 && sscanf(p, "/%d", &nr) != 1)
+	       || nr < 0)
+		goto done;
+
+	ctl = open(_PATH_DEV_LOOPCTL, O_RDWR|O_CLOEXEC);
+	if (ctl >= 0) {
+		DBG(CXT, ul_debugobj(lc, "add_device %d", nr));
+		rc = ioctl(ctl, LOOP_CTL_ADD, nr);
+		close(ctl);
+	}
+	lc->control_ok = rc >= 0 ? 1 : 0;
+done:
+	DBG(CXT, ul_debugobj(lc, "add_device done [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * Note that LOOP_CTL_GET_FREE ioctl is supported since kernel 3.1. In older
+ * kernels we have to check all loop devices to found unused one.
+ *
+ * See kernel commit 770fe30a46a12b6fb6b63fbe1737654d28e8484.
+ *
+ * Returns: 0 = success, < 0 error
+ */
+int loopcxt_find_unused(struct loopdev_cxt *lc)
+{
+	int rc = -1;
+
+	DBG(CXT, ul_debugobj(lc, "find_unused requested"));
+
+	if (lc->flags & LOOPDEV_FL_CONTROL) {
+		int ctl;
+
+		DBG(CXT, ul_debugobj(lc, "using loop-control"));
+
+		ctl = open(_PATH_DEV_LOOPCTL, O_RDWR|O_CLOEXEC);
+		if (ctl >= 0)
+			rc = ioctl(ctl, LOOP_CTL_GET_FREE);
+		else
+			rc = -errno;
+		if (rc >= 0) {
+			char name[16];
+			snprintf(name, sizeof(name), "loop%d", rc);
+
+			rc = loopiter_set_device(lc, name);
+		}
+		lc->control_ok = ctl >= 0 && rc == 0 ? 1 : 0;
+		if (ctl >= 0)
+			close(ctl);
+		DBG(CXT, ul_debugobj(lc, "find_unused by loop-control [rc=%d]", rc));
+	}
+
+	if (rc < 0) {
+		DBG(CXT, ul_debugobj(lc, "using loop scan"));
+		rc = loopcxt_init_iterator(lc, LOOPITER_FL_FREE);
+		if (rc)
+			return rc;
+
+		rc = loopcxt_next(lc);
+		loopcxt_deinit_iterator(lc);
+		DBG(CXT, ul_debugobj(lc, "find_unused by scan [rc=%d]", rc));
+		if (rc)
+			return -ENOENT;
+	}
+	return rc;
+}
+
+
+
+/*
+ * Return: TRUE/FALSE
+ */
+int loopdev_is_autoclear(const char *device)
+{
+	struct loopdev_cxt lc;
+	int rc;
+
+	if (!device)
+		return 0;
+
+	rc = loopcxt_init(&lc, 0);
+	if (!rc)
+		rc = loopcxt_set_device(&lc, device);
+	if (!rc)
+		rc = loopcxt_is_autoclear(&lc);
+
+	loopcxt_deinit(&lc);
+	return rc;
+}
+
+char *loopdev_get_backing_file(const char *device)
+{
+	struct loopdev_cxt lc;
+	char *res = NULL;
+
+	if (!device)
+		return NULL;
+	if (loopcxt_init(&lc, 0))
+		return NULL;
+	if (loopcxt_set_device(&lc, device) == 0)
+		res = loopcxt_get_backing_file(&lc);
+
+	loopcxt_deinit(&lc);
+	return res;
+}
+
+/*
+ * Returns: TRUE/FALSE
+ */
+int loopdev_has_backing_file(const char *device)
+{
+	char *tmp = loopdev_get_backing_file(device);
+
+	if (tmp) {
+		free(tmp);
+		return 1;
+	}
+	return 0;
+}
+
+/*
+ * Returns: TRUE/FALSE
+ */
+int loopdev_is_used(const char *device, const char *filename,
+		    uint64_t offset, uint64_t sizelimit, int flags)
+{
+	struct loopdev_cxt lc;
+	struct stat st;
+	int rc = 0;
+
+	if (!device || !filename)
+		return 0;
+
+	rc = loopcxt_init(&lc, 0);
+	if (!rc)
+		rc = loopcxt_set_device(&lc, device);
+	if (rc)
+		return rc;
+
+	rc = !stat(filename, &st);
+	rc = loopcxt_is_used(&lc, rc ? &st : NULL, filename, offset, sizelimit, flags);
+
+	loopcxt_deinit(&lc);
+	return rc;
+}
+
+/*
+ * Returns: 0 = success, < 0 error
+ */
+int loopdev_delete(const char *device)
+{
+	struct loopdev_cxt lc;
+	int rc;
+
+	if (!device)
+		return -EINVAL;
+
+	rc = loopcxt_init(&lc, 0);
+	if (!rc)
+		rc = loopcxt_set_device(&lc, device);
+	if (!rc)
+		rc = loopcxt_delete_device(&lc);
+	loopcxt_deinit(&lc);
+	return rc;
+}
+
+/*
+ * Returns: 0 = success, < 0 error, 1 not found
+ */
+int loopcxt_find_by_backing_file(struct loopdev_cxt *lc, const char *filename,
+				 uint64_t offset, uint64_t sizelimit, int flags)
+{
+	int rc, hasst;
+	struct stat st;
+
+	if (!filename)
+		return -EINVAL;
+
+	hasst = !stat(filename, &st);
+
+	rc = loopcxt_init_iterator(lc, LOOPITER_FL_USED);
+	if (rc)
+		return rc;
+
+	while ((rc = loopcxt_next(lc)) == 0) {
+
+		if (loopcxt_is_used(lc, hasst ? &st : NULL,
+				    filename, offset, sizelimit, flags))
+			break;
+	}
+
+	loopcxt_deinit_iterator(lc);
+	return rc;
+}
+
+/*
+ * Returns: 0 = not found, < 0 error, 1 found, 2 found full size and offset match
+ */
+int loopcxt_find_overlap(struct loopdev_cxt *lc, const char *filename,
+			   uint64_t offset, uint64_t sizelimit)
+{
+	int rc, hasst;
+	struct stat st;
+
+	if (!filename)
+		return -EINVAL;
+
+	DBG(CXT, ul_debugobj(lc, "find_overlap requested"));
+	hasst = !stat(filename, &st);
+
+	rc = loopcxt_init_iterator(lc, LOOPITER_FL_USED);
+	if (rc)
+		return rc;
+
+	while ((rc = loopcxt_next(lc)) == 0) {
+		uint64_t lc_sizelimit, lc_offset;
+
+		rc = loopcxt_is_used(lc, hasst ? &st : NULL,
+				     filename, offset, sizelimit, 0);
+		/*
+		 * Either the loopdev is unused or we've got an error which can
+		 * happen when we are racing with device autoclear. Just ignore
+		 * this loopdev...
+		 */
+		if (rc <= 0)
+			continue;
+
+		DBG(CXT, ul_debugobj(lc, "found %s backed by %s",
+			loopcxt_get_device(lc), filename));
+
+		rc = loopcxt_get_offset(lc, &lc_offset);
+		if (rc) {
+			DBG(CXT, ul_debugobj(lc, "failed to get offset for device %s",
+				loopcxt_get_device(lc)));
+			continue;
+		}
+		rc = loopcxt_get_sizelimit(lc, &lc_sizelimit);
+		if (rc) {
+			DBG(CXT, ul_debugobj(lc, "failed to get sizelimit for device %s",
+				loopcxt_get_device(lc)));
+			continue;
+		}
+
+		/* full match */
+		if (lc_sizelimit == sizelimit && lc_offset == offset) {
+			DBG(CXT, ul_debugobj(lc, "overlapping loop device %s (full match)",
+						loopcxt_get_device(lc)));
+			rc = 2;
+			goto found;
+		}
+
+		/* overlap */
+		if (lc_sizelimit != 0 && offset >= lc_offset + lc_sizelimit)
+			continue;
+		if (sizelimit != 0 && offset + sizelimit <= lc_offset)
+			continue;
+
+		DBG(CXT, ul_debugobj(lc, "overlapping loop device %s",
+			loopcxt_get_device(lc)));
+			rc = 1;
+			goto found;
+	}
+
+	if (rc == 1)
+		rc = 0;	/* not found */
+found:
+	loopcxt_deinit_iterator(lc);
+	DBG(CXT, ul_debugobj(lc, "find_overlap done [rc=%d]", rc));
+	return rc;
+}
+
+/*
+ * Returns allocated string with device name
+ */
+char *loopdev_find_by_backing_file(const char *filename, uint64_t offset, uint64_t sizelimit, int flags)
+{
+	struct loopdev_cxt lc;
+	char *res = NULL;
+
+	if (!filename)
+		return NULL;
+
+	if (loopcxt_init(&lc, 0))
+		return NULL;
+	if (loopcxt_find_by_backing_file(&lc, filename, offset, sizelimit, flags) == 0)
+		res = loopcxt_strdup_device(&lc);
+	loopcxt_deinit(&lc);
+
+	return res;
+}
+
+/*
+ * Returns number of loop devices associated with @file, if only one loop
+ * device is associated with the given @filename and @loopdev is not NULL then
+ * @loopdev returns name of the device.
+ */
+int loopdev_count_by_backing_file(const char *filename, char **loopdev)
+{
+	struct loopdev_cxt lc;
+	int count = 0, rc;
+
+	if (!filename)
+		return -1;
+
+	rc = loopcxt_init(&lc, 0);
+	if (rc)
+		return rc;
+	if (loopcxt_init_iterator(&lc, LOOPITER_FL_USED))
+		return -1;
+
+	while(loopcxt_next(&lc) == 0) {
+		char *backing = loopcxt_get_backing_file(&lc);
+
+		if (!backing || strcmp(backing, filename) != 0) {
+			free(backing);
+			continue;
+		}
+
+		free(backing);
+		if (loopdev && count == 0)
+			*loopdev = loopcxt_strdup_device(&lc);
+		count++;
+	}
+
+	loopcxt_deinit(&lc);
+
+	if (loopdev && count > 1) {
+		free(*loopdev);
+		*loopdev = NULL;
+	}
+	return count;
+}
+
+#ifdef TEST_PROGRAM_LOOPDEV
+int main(int argc, char *argv[])
+{
+	if (argc < 2)
+		goto usage;
+
+	if (strcmp(argv[1], "--is-loopdev") == 0 && argc == 3)
+		printf("%s: %s\n", argv[2], is_loopdev(argv[2]) ? "OK" : "FAIL");
+	else
+		goto usage;
+
+	return EXIT_SUCCESS;
+usage:
+	fprintf(stderr, "usage: %1$s --is-loopdev <dev>\n",
+			program_invocation_short_name);
+	return EXIT_FAILURE;
+}
+#endif
+