Hi, I will try to make my question more clear. I would like to put a box between the client and the storage, and to be fully transparent against the host. All changes on the storage (add/remove/extend devices) should be present automatically to the client. In a direct connection between client and storage the administrator will coordinate between the client and storage before making any changes, in my configuration I do not want to add administration work on my box that stands between the client and the storage. Addition is simple, the application on my box can once in a while scan the SCSI BUS, and then the Linux system will create new sg devices. In removal of a device the Linux system will not remove sg devices after scan. In that case again I can do it from my application, such when I get attention on SCSI command, I can decide to remove the device by echoing to the /sys file system. What do you think ? is this enough or there is better way ? Thanks, Gal. On Mon, 2008-07-28 at 15:10 +0200, Stefan Richter wrote: > Gal Rosen wrote: > > I know that when adding new device there is no problem; > > by echo "- - -" >/sys/class/scsi_host/hostX/scan the SCSI subsystem will > > recognize the new device and new /dev/sgX device will be created, but if > > someone remove a device, scan will only recognize that the report luns > > has changed, but it will not remove the /dev/sgX device. > > If now someone add new device it will mapped to the /dev/sgX that > > previously mapped to the device that just removed. > > > > 1. Why the SCSI subsystem doesn't release devices that removed ? > > Because somewhere someone still holds a reference on the device (for a > good reason, or due to a bug). > > > 2. In the situation that I described above someone can switched devices > > without notifying the application that use those devices. The > > notification will come only when the next SCSI command will return with > > unit attention saying "Power on, reset, or bus device reset occured", or > > if device just removed without adding new device it will return > > "Reported luns data has changed". > > If I have an application that control SCSI devices using sg driver and I > > would like to have the ability to change configuration online, what is > > the preferred way to rescan the bus and update the application that sgX > > that previously controls device Y is now controlling device Z ? > > In other words, what is the best way for the application to identify > > that device has been removed or changed ? > > Hmm, I too am curious what the answer to this would be. > > > 3. I am using Qlogic firmware ability to create virtual ports, and I > > notice that on disconnect and then reconnect the FC cable, the sg > > mapping can changed. If on module load the physical port got sg0, and on > > creating vport it got sg1, now the SCSI subsystem scans the vport first > > and mapped it to sg0 and the physical port gets sg1. > > Is there a way to control the mapping (scanning) ? > > There is currently one canonical way: The low-level userspace (udev, > hal, or even your application) looks at the device representation in > sysfs and fetches persistent and unique properties of the target and > logical unit from there. The target identifier and logical unit > identifier come first to mind as suitable properties. Then the > low-level userspace can for example create symlinks. Most distributions > contain udev scripts which do this for sd devices; see /dev/disk/by-id/. > > Alas there is no standard place where to look for target identifier and > logical unit identifier. At least at the last time when I looked for > them, the paths to respective sysfs attributes are so far implementation > details of the various transport-layer drivers or so-called transport > classes (FC, SAS, iSCSI, SBP-2...). -- 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
