Hi, James (2011/04/09 0:14), James Bottomley wrote: > On Fri, 2011-04-08 at 07:33 -0700, Hannes Reinecke wrote: >>> The problem I would like to discuss here is that users can not identify >>> a disk from kernel messages when they DIRECTLY refer to these messages. >>> For example, a device name is used instead of a symbolic link names in >>> bootup messages, I/O devices errors and /proc/partitions âetc. >>> >>> In particular, users can not identify an appropriate device from a >>> device name in syslog since different device name may be assigned to it >>> at each boot time. >>> >>> My idea is able to fix this issue with small changes in scsi subsystem. >>> Also, it is implemented as an option. Therefore, it does not affect >>> users who do not select this option. >>> >> We have been discussing this problem several times in the past, and >> indeed on these very mailing list. >> >> The conclusion we arrived at is that the kernel-provided device node >> name is inherently unstable and impossible to fix within the existing >> 'sdX' naming scheme. >> So the choices have been to either move to a totally different naming >> scheme or keep the naming scheme and provide the required information >> by other means. >> We have decided on the latter, and agreed on using udev to provide >> persistent device names. >> We are fully aware that any kernel related messages are subject to >> chance after reboot, but then most kernel related messages are >> (PID number, timestamps, login tty etc). >> And also we are aware that any kernel messages need to be matched >> against the current system layout to figure out any hardware-related >> issue. >> >> But then basically all products requiring to filter out information >> from kernel messages already do so I don't see a problem with that. >> >> Just adding an in-kernel identifier to the LUN will only be an >> incomplete solution, as other identifiers will still be volatile. >> >> So I would prefer by keeping the in-kernel information as small >> as possible to reduce memory consumption and rely on out-of-band >> programs to provide the required mapping. > > So, while I agree totally with the above: udev and userspace is the way > to go, I'm not totally opposed to having a non-invasive mechanism for > indicating a user's preferred name for a device. I think there are a > couple of ways to do this: > > 1. Entirely in userspace: just have udev consult a preferred name > file and create say /dev/disk/by-preferred. Then have all the > tools that normally output device information do the same (i.e. > since real name to preferred name is 1:1, they could all do a > reverse lookup). > 2. have a writeable sysfs preferred_name field, either in the > generic device or just in SCSI. The preferred name would be > used by outbound only (i.e. kernel dev_printk messages and > possibly /proc/partitions). All inbound uses of the device > would come via the standard udev mechanisms > (i.e. /dev/disk/by-preferred would be the usual symlink). This > means from the kernel point of view, no renaming has happened. > We'd just try to print out the preferred name in certain > circumstances, which should solve most of the described problem. > > James > > > I have a question. Why is in-kernel device name necessary? The kernel can identify a device by major/miner number and udev can create a device node of a prefer name. Currently, device names are only used to show to users. Therefore I think that in-kernel device name is unnecessary if we introduce your /dev/disk/by-prefferd idea. thanks, -- Nao NISHIJIMA Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., YOKOHAMA Research Laboratory Emailï nao.nishijima.xt@xxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
