Ok so in fact the inconsistency is due to "parted" that will try to
probe devices iff the given block device return informations from
stat(), regardless if the block device is available or not.
Seems like the only trigger/criteria is the stat() return. Since the
loop device stat doesn't clear/reset once umounted/detacted, then parted
assume it can go ahead and probe it assuming it is a legit device.
----
# libparted/arch/linux.c
----
618 static int
619 _device_stat (PedDevice* dev, struct stat * dev_stat)
620 {
621 PED_ASSERT (dev != NULL);
622 PED_ASSERT (!dev->external_mode);
623
624 while (1) {
625 if (!stat (dev->path, dev_stat)) {
626 return 1;
627 } else {
628 if (ped_exception_throw (
629 PED_EXCEPTION_ERROR,
630 PED_EXCEPTION_RETRY_CANCEL,
631 _("Could not stat device %s - %s."),
632 dev->path,
633 strerror (errno))
634 != PED_EXCEPTION_RETRY)
635 return 0;
636 }
637 }
638 }
----
Example:
----
# parted -s $(losetup -f) unit s print
Warning: Error fsyncing/closing /dev/loop18: Input/output error
# stat $(losetup -f)
File: /dev/loop18
Size: 0 Blocks: 0 IO Block: 4096 block special file
Device: 6h/6d Inode: 509 Links: 1 Device type: 7,12
Access: (0660/brw-rw----) Uid: ( 0/ root) Gid: ( 6/ disk)
Access: 2019-12-25 13:05:15.543108777 -0500
Modify: 2019-12-25 13:05:15.543108777 -0500
Change: 2019-12-25 13:05:15.543108777 -0500
Birth: -
# parted -s /dev/loop19 unit s print
Error: Could not stat device /dev/loop19 - No such file or directory.
# stat /dev/loop19
stat: cannot stat '/dev/loop19': No such file or directory
----
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https://bugs.launchpad.net/bugs/1856871
Title:
i/o error if next unused loop device is queried
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