Hi there, I'm the author of Upstart (the init system used by Ubuntu, and other distributions) and was directed to the following page in order to update compatibility with newer kernels and libata: http://linux-ata.org/shutdown.html Unfortunately after reading this, things still aren't entirely clear to me. Right now, Upstart is using roughly the same halt/reboot code as sysvinit -- this has rather a lot of baggage, so I've been trying to slim it down recently, and thus reading the same code paths you seem to have been. If you could help me through my confusion, that would be greatly appreciated. "In ATA, this is achieved by issuing FLUSH CACHE followed by STANDBYNOW and the IDE drivers (drivers/ide/*) have always issued the sequence prior to powering off." This is the code path I've been looking through, and I concur with your assessment. IDE drives using the IDE subsystem are powered down (by generic_ide_suspend() called by ide_device_shutdown) The sysvinit in Debian (and Upstart in Ubuntu) use the following procedure during shutdown: * sync() * Open /proc/ide, iterate all hd* devices found there * Check /proc/ide/*/media is "disk" * Open the device in /dev * Issue WIN_STANDBYNOW1 * Issue WIN_STANDBYNOW2 No attempt is made to flush the disk cache, other than calling sync(). Firstly, since it appears that the kernel already takes care of flushing the cache and standbying the disk, it would appear that this code in our halt/reboot binary is entirely useless. In some cases this would mean that the drive was placed into standby, before the kernel flushes its caches, bringing the drive out of standby with the clicking sound. (For the *IDE* subsystem, not libata). Can we simply drop this code entirely? (I've been of the opinion we can, but it's nice to get expert confirmation). Secondly, we've never attempted any workarounds for libata. Our halt/reboot only iterates /proc/ide, which should be empty for libata-based systems - therefore we've never issued FLUSH CACHE or STANDBYNOW on libata drives from userspace. In this case, how should we proceed? * Check whether /sys/modules/libata/parameters/spindown_compat exists. If it does, write 0 to it. Since we've never been broken, can we not arrange for this to be always zero? Perhaps just writing to it on boot? For each libata harddisk * Check whether /sys/class/scsi_disk/h:c:i:l/manage_start_stop exists. If it doesn't, synchronize cache and spin the disk down as before. If it does, do nothing and continue to the next disk. The file is also accessible as /sys/block/sdX/device/scsi_disk:*/manage_start_stop. What's the reason for needing to flush the cache and standby the disk by hand? What are the circumstances where the manage_start_stop will not exist? Obviously I'd rather our halt/reboot binary was literally a thin wrapper around the reboot() system call, without special logic. Since we're going to have to code the above logic, I'd like to make sure it's going in the right place. Also what's the canon way to synchronise the cache and spin the disk down? How do we iterate libata harddisks, and map to the correct name in /dev ? Scott -- Scott James Remnant Ubuntu Development Manager scott@xxxxxxxxxx
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