losetup -l
NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE                             DIO LOG-SEC
/dev/loop1         0      0         1  1 /var/lib/snapd/snaps/core_7270.snap     0     512
/dev/loop2         0      0         1  1 /var/lib/snapd/snaps/core_8268.snap     0     512
/dev/loop0         0      0         1  1 /var/lib/snapd/snaps/firefox_287.snap   0     512


# losetup -f
/dev/loop3

# strace parted -s $(losetup -f) unit s print
ioctl(3, BLKSSZGET, [512])              = 0
fadvise64(3, 0, 0, POSIX_FADV_RANDOM)   = 0
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 3), ...}) = 0
ioctl(3, BLKGETSIZE64, [0])             = 0
openat(AT_FDCWD, "/sys/dev/block/7:3", O_RDONLY|O_CLOEXEC) = 4
openat(4, "dm/uuid", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
close(4)                                = 0
ioctl(3, BLKALIGNOFF, [0])              = 0
ioctl(3, BLKIOMIN, [512])               = 0
ioctl(3, BLKIOOPT, [0])                 = 0
ioctl(3, BLKPBSZGET, [512])             = 0
ioctl(3, BLKSSZGET, [512])              = 0
ioctl(3, BLKGETSIZE64, [0])             = 0
ioctl(3, BLKGETSIZE64, [0])             = 0
fsync(3)                                = -1 EIO (Input/output error)
openat(AT_FDCWD, "/usr/share/locale/en_US.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en_US.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en_US.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2, "Warning", 7Warning)                  = 7
write(2, ": ", 2: )                       = 2
write(2, "Error fsyncing/closing /dev/loop"..., 53Error fsyncing/closing /dev/loop3: Input/output error) = 53
write(2, "\n", 1
)                       = 1
close(1)                                = 0
close(2)                                = 0
exit_group(1)                           = ?
+++ exited with 1 +++


# strace parted -s /dev/loop5 unit s print

ioctl(3, BLKSSZGET, [512])              = 0
fadvise64(3, 0, 0, POSIX_FADV_RANDOM)   = 0
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 5), ...}) = 0
ioctl(3, BLKGETSIZE64, [0])             = 0
openat(AT_FDCWD, "/sys/dev/block/7:5", O_RDONLY|O_CLOEXEC) = 4
openat(4, "dm/uuid", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
close(4)                                = 0
ioctl(3, BLKALIGNOFF, [0])              = 0
ioctl(3, BLKIOMIN, [512])               = 0
ioctl(3, BLKIOOPT, [0])                 = 0
ioctl(3, BLKPBSZGET, [512])             = 0
ioctl(3, BLKSSZGET, [512])              = 0
ioctl(3, BLKGETSIZE64, [0])             = 0
ioctl(3, BLKGETSIZE64, [0])             = 0
fsync(3)                                = 0
close(3)                                = 0
close(1)                                = 0
close(2)                                = 0
exit_group(1)                           = ?
+++ exited with 1 +++