On Mon, 9 April 2007 12:21:15 -0500, Eric Sandeen wrote: > Phillip Susi wrote: > > > > When the filesystem is told to mount the disk read only, that means it > > should not write to it. > > It means the filesystem should not be writeable when it is mounted. > This is not the same as saying that the filesystem itself should do no > IO in the course of making that read-only mount available. The filesystem has two interfaces. One to the device underneith, one to userspace. Read-only should certainly mean that no writes cross the userspace interface. Traditionally it has implicitly also meant that no writes are crossing the device interface. Whether that was/is an explicit requirement - who knows. Journaling filesystems have introduced this thing called "journal replay". And I have to admit, it makes thing _a lot_ easier to always replay the journal, even when being mounted read-only. But "it is easier" is a pretty lame excuse. > Under all conditions it should be safe to mount a read-only block > device, but that is not the same as mounting a filesystem read-only. In particular, it is a lame excuse when this claim is true. If the block-device is read-only, then journal replay will not work as expected and all the "not so easy" work has to be done anyway. Did I miss anything? Is it actually easier to mount a read-only device with unclean journal than mounting a read-write device and not replay the journal? Jörn -- Joern's library part 8: http://citeseer.ist.psu.edu/plank97tutorial.html - 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
