On Thu, Dec 01 2022 at 11:38P -0500, Peter Korsgaard <peter@xxxxxxxxxxxxx> wrote: > >>>>> "Mike" == Mike Snitzer <snitzer@xxxxxxxxxx> writes: > > Hi, > > >> As mentioned, > >> https://lore.kernel.org/all/20220406154631.277107-1-fabio.aiuto@xxxxxxxxxxxxxxxxxxxx/ > >> is an alternatively (less nice) approach to solve the same issue, so yes > >> - It is useful and needed. > > > OK, so it should be easy for others to say so, right? > > Yes. Fabio, you pointed me to the earlier patch, so you presumably need > something like this as well, right? > > > > My hesitation is that it feels like something that could be papering > > over device specific issues with their async initialization? Even if > > that is the case, it'd be nice to know _why_ this change is needed. > > IMHO, the patch header stops short of offering compelling and informed > > justification. > > Well, it is exactly like the rootwait option we have for normal (non-dm) > root= handling, so it is for the same use cases / issues. > > A lot of embedded / non-initramfs setups use rootwait today because of > the async initialization logic. If those setups want to use root-on-dm > (E.G. for dm-verity) then they need to use this dm_mod.waitfor= instead > of rootwait. > > rootwait was added by: > > commit cc1ed7542c8c26af0f501da8006b9fce03e9aaca > Author: Pierre Ossman <drzeus-list@xxxxxxxxx> > Date: Sun Jul 15 23:40:35 2007 -0700 > > init: wait for asynchronously scanned block devices > > Some buses (e.g. USB and MMC) do their scanning of devices in the > background, causing a race between them and prepare_namespace(). In order > to be able to use these buses without an initrd, we now wait for the device > specified in root= to actually show up. > > If the device never shows up than we will hang in an infinite loop. In > order to not mess with setups that reboot on panic, the feature must be > turned on via the command line option "rootwait". > > [bunk@xxxxxxxxx: root_wait can become static] > Signed-off-by: Pierre Ossman <drzeus@xxxxxxxxx> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > Signed-off-by: Adrian Bunk <bunk@xxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> OK, I'll accept your patch, but will tweak the DMINFO slightly to look more like rootwait's pr_info (e.g. "Waiting for device %s..." and such). I'll also change the msleep(20) to msleep(5) like was introduced with commit 39a0e975c37de ("init: reduce rootwait polling interval time to 5ms") -- checkpatch be damned. ;) Thanks, Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
