On 02/07/2011 03:41 PM, James Bottomley wrote: > On Mon, 2011-02-07 at 03:53 -0800, Joel Becker wrote: >> On Mon, Feb 07, 2011 at 12:41:18PM +0100, Bart Van Assche wrote: >>> On Fri, Feb 4, 2011 at 7:45 AM, Nicholas A. Bellinger >>> <nab@xxxxxxxxxxxxxxx> wrote: >>>> Please consider the following patch series for mainline target code. >>>> It consists of predominately configfs bugfixes uncovered with recent SLUB >>>> poison testing, and proper removal of legacy procfs target_core_mib.c code. >>>> Note that the complete set of fabric independent statistics (SCSI MIBs) and >>>> fabric dependent statistics will be included as native configfs group context >>>> 'per value' attribute series during the .39 time frame. >>> >>> I'm still not convinced that using configfs in a storage target as the >>> only interface between kernel space and user space is a good idea. >>> While configfs may satisfy all the needs of an iSCSI target, the use >>> of configfs in combination with hot-pluggable HCAs is really awkward. >>> Whenever a HCA is plugged in, the user has to issue mkdir commands to >>> make these interfaces appear in configfs. And whenever a HCA is >>> removed, stale information will remain present in configfs until the >>> user issues an rmdir command. As we all know, it is not possible for a >>> storage target to make these directories appear / disappear >>> automatically in configfs because of basic configfs design choices. >> >> Any configuration would have to be handled. We have plenty of >> stuff that is handled by userspace hooks out of udev, etc. That's a >> normal hotplug process. >> Essentially, you're not challenging Nick's use of configfs here, >> you're challenging his environment of setting up the target stack from >> userspace. > > I think the overall philosophical point here, and it's a good one > because I've heard it from several sources, is that it's not possible to > separate configuration from status completely. The classic example is > where the kernel has to validate and adjust config information, but the > storage specific one is where events alter the topology. In either > case, the configfs tree gets out of sync with reality if the kernel does > the adjustment.. Just saying we have to use a user space tool to fix it > up is a bit of a cop out because the kernel has already adjusted its own > configuration, so getting userspace to work out what the kernel's done > and adjust configfs is a bit sub optimal. > This sounds exactly like the familiar problem we have on zSeries; devices are being configured via sysfs but require a separate store to hold the information if the device doesn't happen to be present. What we came up with is a) Devices which are not configured won't be activated. Essentially this means you have to have a configuration for each device (_not_ stored in sysfs, obviously), and use this as the primary config. If and when the device becomes available, udev will use this information to configure the device. b) If the device state changes either the device is smart enough to handle it internally or the correct events have to be send out via udev to allow proper configuration here. And yes, without udev that wouldn't work. If you have a problem with this, you can stop reading now. Applying this to configfs we need to define a configuration file format, and a set of udev rules which would use this information to configure the configfs tree. Of course, it would be preferable to have target_core to update the information itself (eg for device removal). If that wouldn't be possible we need to insure that the configfs part doesn't crash if the underlying device is removed but rather returns sensible errors when accessed. But I don't see any principle problem here. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 NÃrnberg GF: Markus Rex, HRB 16746 (AG NÃrnberg) -- 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
