Hello, mounting an ext2 (ext3 as well) filesystem seems to modify the block device's EOF behaviour: before the mount the device returned EOF, after the mount it doesn't anymore:
[on a fresh booted system] [EMAIL PROTECTED]:~# uname -a Linux darkside 2.4.27 #1 Sat Jan 15 17:07:20 CET 2005 i686 GNU/Linux [EMAIL PROTECTED]:~# dd if=/dev/hdg7 of=/dev/null 9992366+0 records in 9992366+0 records out 5116091392 bytes transferred in 87,157394 seconds (58699453 bytes/sec) [EMAIL PROTECTED]:~# mke2fs /dev/hdg7 ... Block size=4096 (log=2) Fragment size=4096 (log=2) 625248 inodes, 1249045 blocks ... [EMAIL PROTECTED]:~# dd if=/dev/hdg7 of=/dev/null 9992366+0 records in 9992366+0 records out 5116091392 bytes transferred in 87,439332 seconds (58510184 bytes/sec) [EMAIL PROTECTED]:~# mount -t ext2 -o ro /dev/hdg7 /mnt [EMAIL PROTECTED]:~# umount /dev/hdg7 [EMAIL PROTECTED]:~# dd if=/dev/hdg7 of=/dev/null attempt to access beyond end of device 22:07: rw=0, want=4996184, limit=4996183 dd: reading `/dev/hdg7': Input/output error 9992360+0 records in 9992360+0 records out 5116088320 bytes transferred in 87,145443 seconds (58707468 bytes/sec) [EMAIL PROTECTED]:~# bc 1249045 * 4 4996180 1249045 * 4 * 2 9992360 Could somebody please explain this to me? Is this intentional? I could partly imagine the ext2 mount shrinking the block device's boundaries to the filesystem boundaries - for security reasons perhaps, even if I personally think this isn't the best idea at all, since it would violate layers encapsulation. However, I have no idea why a) if so, this is not reverted at least on umount and why b) the EOF behaviour of the block device changes - before there were an EOF sent to the application (dd) while after there isn't, but an I/O error instead. Kernel is Debian's kernel-source-2.4.27 + kernel-patch-2.4-i2c + kernel-patch-2.4-lm-sensors. It seems there were already some mails regarding this issue suggesting this could have shown up between 2.4.24 and 2.4.25, but it seems they were misunderstood, for example: From: "ProNIC Solutions" <[EMAIL PROTECTED]> Subject: 2.4.25: attempt to access beyond end of device Date: Tue, 16 Mar 2004 09:06:31 -0500 Message-ID: <[EMAIL PROTECTED]> From: "Peter S. Mazinger" <[EMAIL PROTECTED]> Subject: BUG in 2.4.25-rc1: attempt to access beyond end of device Date: Fri, 6 Feb 2004 13:53:40 +0100 (CET) Message-ID: <[EMAIL PROTECTED]> regards Mario -- Independence Day: Fortunately, the alien computer operating system works just fine with the laptop. This proves an important point which Apple enthusiasts have known for years. While the evil empire of Microsoft may dominate the computers of Earth people, more advanced life forms clearly prefer Mac's. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
