On Fri, Jan 09, 2015 at 03:51:23AM +0000, Al Viro wrote: > On Fri, Jan 09, 2015 at 03:44:16AM +0000, Dexuan Cui wrote: > > The 'mount' utility allows me to mount 1 file systems multiple times at different > > mount points, like "mount /dev/sdb1 /a; mount /dev/sdb1 /b". > > > > I tried to write from /a and /b at the same time and it seems everything is OK > > and no data corruption happens. > > I tried only ext4 only. > > > > Can somebody please tell me if this usage is safe? > > Yes. Can you explain under what conditions mounting the same file system twice will work? I guess the kernel is looking up the block device and then sharing the superblock if the file system is already mounted on this block device? If I use two loop devices for the same underlying storage it does not work: # mount -o loop /var/tmp/ext4.img /tmp/a # mount -o loop /var/tmp/ext4.img /tmp/b # touch /tmp/a/a # ls /tmp/b lost+found # umount /tmp/a # umount /tmp/b # mount -o loop /var/tmp/ext4.img /tmp/a [1078357.297245] EXT4-fs error (device loop0): ext4_lookup:1441: inode #2: comm ls: deleted inode referenced: 12 Stefan
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