On 25.10.2012 16:43, Lukáš Czerner wrote: > On Thu, 25 Oct 2012, Michael Tokarev wrote: > >> Date: Thu, 25 Oct 2012 12:39:57 +0400 >> From: Michael Tokarev <mjt@xxxxxxxxxx> >> To: linux-ext4@xxxxxxxxxxxxxxx >> Cc: sandeen@xxxxxxxxxx, Michael Tokarev <mjt@xxxxxxxxxx> >> Subject: [PATCH] ext4: do not try to write superblock on journal-less readonly >> remount >> >> When a journal-less ext4 filesystem is mounted on a read-only block >> device (blockdev --setro will do), each remount (for other, unrelated, >> flags, like suid=>nosuid etc) results in a series of scary messages >> from kernel telling about I/O errors on the device. > > Hi Michael, > > I am not able to reproduce the problem you're seeing: > > mkfs.ext4 /dev/sdd1 > tune2fs -O ^has_journal /dev/sdd1 > blockdev --setro /dev/sdd1 > mount /dev/sdd1 /mnt/test > > and then > > mount -o remount,suid /dev/sdd1 > mount -o remount,nosuid /dev/sdd1 > mount -o remount,noatime /dev/sdd1 > mount -o remount,relatime /dev/sdd1 > mount -o remount,relatime,commit=20 /dev/sdd1 > > just does not produce any errors. Both /var/log/messages and dmesg > are clear. Interesting. Actual situation where I observed this issue was when the device really was read-only. In my case it was a virtual machine (kvm) with a read-only virtio drive (-drive file=foo,if=virtio,readonly=on). I played with a "live CD"-type system. Now when I look at it, I'm not sure if I were really able to reproduce it with regular /dev/sdNN and blockdev --setro. I *think* it was reproducible, but actually I can't. So it looks like blockdev --setro does not do what it claims to do -- the actual device isn't really set read-only. The errors produced at remount are real, when the device in question really dislikes (reject) writes. Apparently --setro isn't enough -- somewhere at kernel level write for such device are actually succeeded instead of being errored out, when the device itself does not reject writes. So the impact is even less severe when I initially thought. Thanks, /mjt -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
