On 4/19/22 20:55, Jens Axboe wrote: > On 4/19/22 5:00 AM, Damien Le Moal wrote: >> Currently, the directory name used to create a nullb device through >> sysfs is not used as the device name, potentially causing headaches for >> users if devices are already created through the modprobe operation >> withe the nr_device module parameter not set to 0. E.g. a user can do >> "mkdir /sys/kernel/config/nullb/nullb0" to create a nullb device while >> /dev/nullb0 wasalready created from modprobe. In this case, the configfs > ^^^ > > space Re-sending to fix this. Also realized that using "#define pr_fmt" would simplify patch 3. Updating that. > >> nullb device will be named nullb1, causing confusion for the user. >> >> Simplify this by using the configfs directory name as the nullb device >> name, always, unless another nullb device is already using the same >> name. E.g. if modprobe created nullb0, then: >> >> $ mkdir /sys/kernel/config/nullb/nullb0 >> mkdir: cannot create directory '/sys/kernel/config/nullb/nullb0': File >> exists >> >> will be reported to th user. >> >> To implement this, the function null_find_dev_by_name() is added to >> check for the existence of a nullb device with the name used for a new >> configfs device directory. nullb_group_make_item() uses this new >> function to check if the directory name can be used as the disk name. >> Finally, null_add_dev() is modified to use the device config item name >> as the disk name for new nullb device, for devices created using >> configfs. The naming of devices created though modprobe remains >> unchanged. >> >> Of note is that it is possible for a user to create through configfs a >> nullb device with the same name as an existing device. E.g. > > This is nice, and solves both the confusing part of having > pre-configured devices, but also using the actual directory name as the > device name even if they are not ordered. > > Only odd bit is you can create a device name where a special file of > that name already exists, but I don't think that's solvable in a clean > way and we just need to ignore that. That's arguably a user error, don't > pick names that already exist. Yes. add_disk() will fail if the device name already exist within the "block" device class, but will not complain about anything if the existing device belongs to another class. I could add a "block" class wide check for device name existence in null_find_dev_by_name() instead of only checking the nullb list ? -- Damien Le Moal Western Digital Research
