Date: Thu, 01 Sep 2005 23:49:27 -0500 From: Nathan Lay <nslay@comcast.net> To: freebsd-bugs@freebsd.org Subject: umount -f Message-ID: <4317D9D7.3020801@comcast.net>
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Hi, I noticed a slight problem with umount -f. Now, as I understand it, -f implies forceful which should (you would think) work regardless of whether the associated device is connected or not. Take for example, a USB storage device...its a simple work around to just remember to unmount the file system before unplugging it, but why should it matter if its unplugged or not, umount -f should at least work no? The system will still appear to think the file system is mounted and on a shutdown try to flush the write buffers onto a device thats no longer connected (at least if it was read/write). Its tempting to blame the kernel, but I think it is more umount's fault. I'm pressed on time so I haven't had a chance to look at how umount works, but shouldn't umount -f at least delete those write buffers if the disk isn't connected? That way the system won't fatal trap at halt... See problem recreation below. I was also thinking about trying to write a USB storage daemon (unless someone else is doing it/has done it), umassd, that would monitor connects and record file system information and the associated nodes and even determine how to mount the file system (ie. Suppose you have multiple USB storage devices and you want them to mount in specific places according to fstab, I imagine you can differentiate between them with their volume information) and on disconnect act on the appropriate nodes associated to a specific umass interface. fstab info: /dev/da0s1d /backup ufs rw,noauto 0 0 For (not that it really matters): reeBSD LIGHTBULB.LOCAL 5.4-RELEASE-p6 FreeBSD 5.4-RELEASE-p6 #8: Wed Aug 31 19:39:09 EST 2005 root@LIGHTBULB.LOCAL:/usr/src/sys/i386/compile/LIGHTBULB i386 Observe: LIGHTBULB# lsvfs Filesystem Refs Flags -------------------------------- ----- --------------- msdosfs 0 ufs 4 devfs 1 synthetic cd9660 0 read-only LIGHTBULB# mount /backup LIGHTBULB# lsvfs Filesystem Refs Flags -------------------------------- ----- --------------- msdosfs 0 ufs 5 devfs 1 synthetic cd9660 0 read-only LIGHTBULB# umount -f /backup umount: unmount of /backup failed: Input/output error LIGHTBULB# lsvfs Filesystem Refs Flags -------------------------------- ----- --------------- msdosfs 0 ufs 5 devfs 1 synthetic cd9660 0 read-only After mounting /backup, I unplugged my device and tried to "forcefully" (and this should unmount it even if its disconnected you would think) unmount it and failed, the system still thinks its mounted. Now at halt, the system will try to flush the write buffer to that mount, which doesn't exist, it will timeout and fatal trap (without unmounting the other disks first?) Best Regards, Nathan Lay
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