Am 31.05.2012 04:34, schrieb Dan Williams: > On Wed, May 30, 2012 at 4:32 PM, James Bottomley > <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: >> On Wed, 2012-05-30 at 11:26 -0700, Dan Williams wrote: >>> On Mon, May 28, 2012 at 5:07 AM, James Bottomley >>> <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: >>>> On Mon, 2012-05-28 at 10:00 +0000, maximilian attems wrote: >>>>> On Sun, May 27, 2012 at 10:13:46AM +0100, James Bottomley wrote: >>>>>> scsi_wait_scan was introduced with asynchronous host scanning as a hack >>>>>> for distributions that weren't using proper udev based wait for root to >>>>>> appear in their initramfs scripts. In 2.6.30 Commit >>>>> >>>>>> c751085943362143f84346d274e0011419c84202 >>>>>> Author: Rafael J. Wysocki <rjw@xxxxxxx> >>>>>> Date: Sun Apr 12 20:06:56 2009 +0200 >>>>>> >>>>>> PM/Hibernate: Wait for SCSI devices scan to complete during resume >>>>>> >>>>>> Actually broke scsi_wait_scan because it renders >>>>>> scsi_complete_async_scans() a nop for modular SCSI if you include >>>>>> scsi_scans.h (which this module does). >>>>>> >>>>>> The lack of bug reports is sufficient proof that this module is no >>>>>> longer used. >>>>> >>>>> We do use it in initramfs-tools. >>>>> >>>>> There is quite a number of bug reports moaning about having to boot with >>>>> `scsi_mod.scan=sync'. I didn't pass them on, because I didn't knew that >>>>> the module itself got broken, for example: >>>>> http://bugs.debian.org/616689 >>>> >>>> OK, so what these bugs show is the breakage ... basically scsi_wait_scan >>>> isn't really waiting for the scans to complete. I can fix it in stable >>>> so you can close your bug reports, but if I do, can you also transition >>>> away from using it so I can remove it in 3.5? >>> >>> Is there some other method whereby userspace can sync all driver >>> probing actions? >> >> No, but then there never really was. The theory is you know all the >> disks you need (/ /usr and so on) and you just wait for them to appear >> before mounting them and proceeding with boot. >> >>> We won't need scsi_complete_async_scans() after: >>> >>> http://marc.info/?l=linux-scsi&m=133840132007532&w=2 >>> >>> ...but won't initramfs environments still need a way to trigger >>> wait_for_device_probe()? Something like echo "flush" > >>> /sys/devices/async_probe. and maybe reading that file indicates if >>> some async probing is still in-flight? >> >> Why? The job of an initramfs is to mount root. All it has to do is >> wait for root to appear via udev and then proceed. The whole reason for >> doing stuff async initially was to speed boot, so probing can still be >> ongoing even after the initrd exits. >> >> If you think about it, most modern fabrics are hot plug. Just because >> the initial scan has completed there's no guarantee that all the devices >> have appeared yet. > > Fine for single device root, but what about raid and degraded assembly? > > Last time I checked scsi_wait_scan was still being used by dracut in > the case where it decides to stop waiting for all raid members to > appear. It's a "last call" before proceeding with degraded assembly. > > If you immediately assemble and mount root as soon as the root device > could be started it will almost always be a degraded array. Sure the > initramfs can just timeout arrival, but at a minimum that timeout > should be "load module + flush scanning". Without a flush mechanism > it's just a shot in the dark what that minimum timeout should be. > > If ata error recovery is kicking in and needs 10s of seconds to > recover a drive I'd want my initramfs to wait for that process to > quiesce before timing out and moving on. > > -- > Dan For Fedora17 scsi_wait_scan is not used anymore in the normal initramfs. I removed it and raid is only tried to be started in degraded mode after a timeout (several udevadm settle waits plus some extra 10 seconds). -- 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
