mjhjmtu

I am trying to improve an installation script with interactive selection of source and destination disks. It currently gets the list of entries from /sys/block and filters it through sr[0-9]|sd[a-z]|hd[a-z]|scd[0-5] — effecively excluding other appropriate types of devices. My idea was to remove the hardcoded mask and approach with more general method. As an example of satisfying result, lsblk works as needed by default, and I thought it will be that simple to merely look into its sources to copy the logic, but that was not the case as it turned out.

According to set_cxt() function, the device is excluded if it has size of zero, or is non-SCSI, which in turn is checked by sysfs_blkdev_scsi_get_hctl() — the one I could not get totally through: it is supposed to inspect something (namely, HCTL — Host, Channel, Target, LUN) in the device subtree, which is probably represented by scsi_device and scsi_disk directories, however there is no scsi at all in hda subtree of a memory card device, for example, neither there is a device subtree in etherd!e42.0 of an ATA-over-Ethernet storage, yet they are included in lsblk output by default.

What else may one check to reliably filter out dummy devices like ram15? Those are pre-created in big numbers, having size > 0 and ro = 0, making it hard to distinguish them from regular disks. In simple terms, the result should ideally be identical to lsblk -d -n -o NAME — as a last resort I will just parse that output, but I just wanted to understand the things better myself.