On Fri, Feb 25, 2022 at 07:09:03PM +0100, Christoph Hellwig wrote: > Linux plans to deprecate the auto-creation of block devices based on > access to the devic node starting from kernel 5.18. Without that feature > losetup will fail to create the loop device if a device node already > exists, but the loop device to back it in the kernel does not exist yet. > This is a scenario that should not happen in modern udev based > distributions, but apparently there still are various scripts around that > manually call the superflous mknod. > > Change losetup to unconditionally call loopcxt_add_device when a specific > device node is specified on the command line. If the loop device > already exists the LOOP_CTL_ADD ioctl will fail, but given that losetup > ignores the return value from loopcxt_add_device that failure has no > further effect. I think it would help to explain what the issue is, with a simple example on the commit log. By default loading the loop module we'll create only 8 loopback devices. Prior to the new CONFIG_BLOCK_LEGACY_AUTOLOAD which intends to deprecate the whole oldschool probe functionality which used try to load the respective block driver (loop in this case) when the driver is not present but the nodes are created manually, the following piece of code would work: losetup -D modprobe -r loop modprobe loop rm -f foo.img truncate -s 10M foo.img # Note: /dev/loop8 by default won't exist as we default to 7 # loop devices rm -f /dev/loop8 mknod /dev/loop8 b 7 8 losetup /dev/loop8 foo.img When deprecating this probe --> module load logic, if the mknod is run we'd currently fail at the last step. With this fix the last step will still work. However please note that CONFIG_BLOCK_LEGACY_AUTOLOAD goes away the above will require manually loading the loop module. Scripts which fail to load the loop module prior to mknod will fail by definition of the deprecation effort. > Reported-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > Signed-off-by: Christoph Hellwig <hch@xxxxxx> With that said: Tested-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> Luis > --- > sys-utils/losetup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/sys-utils/losetup.c b/sys-utils/losetup.c > index c400cbf12..09c028b6b 100644 > --- a/sys-utils/losetup.c > +++ b/sys-utils/losetup.c > @@ -522,7 +522,7 @@ static int create_loop(struct loopdev_cxt *lc, > } > } > > - if (hasdev && !is_loopdev(loopcxt_get_device(lc))) > + if (hasdev) > loopcxt_add_device(lc); > > /* losetup --noverlap /dev/loopN file.img */ > -- > 2.30.2 >
