On Tue 13-12-11 12:01:39, Joerg Schilling wrote: > And BTW: given the fact that Linux supports programs like "df", I would guess > that it is possible to do that mapping. Note that unless you do something > really weird (which would be in conflict with the POSIX standard), you always > know the vfs structure for a file and a vfs structure of course has an > associated mount point. Given the fact that in an FS that does not support > hard links to directories (UDF does not, so you are on the easy side) there is > exactly one way to traverse the directory tree upwards, As a result, there is > always exactly one mountpoint related to any leaf fs object. > > AFAIK, Linux does getcwd() in kernel as Solaris does, so it should be possible > to get the path for a mount point, in case that path was not kept during the > mount(2) operation. Jorg, maybe I'm missing something but look: quack:/tmp/foo # l total 700 drwxr-xr-x 2 root root 4096 2011-12-13 16:54 ./ drwxrwxrwt 74 root root 712704 2011-12-13 16:54 ../ quack:/tmp/foo # mkdir -p bar/baz quack:/tmp/foo # mkdir bar2 quack:/tmp/foo # mount -t ext3 -o loop ~jack/fs-images/ext3-image bar/baz/ quack:/tmp/foo # mkdir bar/baz/dir quack:/tmp/foo # touch bar/baz/dir/some_file quack:/tmp/foo # mount --bind bar/baz/dir/ bar2 quack:/tmp/foo # ls bar2 some_file quack:/tmp/foo # ls bar/baz/ aquota.group aquota.user dir quack:/tmp/foo # mount -t ext2 -o loop ~jack/fs-images/ext2-image bar/ quack:/tmp/foo # l bar total 18 drwxr-xr-x 4 10005 users 1024 2011-02-24 12:18 ./ drwxr-xr-x 4 root root 4096 2011-12-13 16:55 ../ drwx------ 2 root root 12288 2010-03-10 12:21 lost+found/ drwxrwxrwx 6 root root 1024 2011-02-24 12:18 t/ quack:/tmp/foo # So to summarize we have directory structure like: /tmp | foo / \ bar bar2 | | here is ext2_image here is subtree of 'dir' from ext3_image And yes, df doesn't work for ext3_image if you do this: quack:/tmp/foo # df Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda2 24843384 8170984 15410424 35% / devtmpfs 488488 240 488248 1% /dev tmpfs 489924 544 489380 1% /dev/shm /dev/mapper/cr_sda3 50007768 36910580 10556904 78% /crypted df: `/tmp/foo/bar/baz': No such file or directory /dev/loop1 63461 63461 0 100% /tmp/foo/bar And yes, if I get into bar/baz and then mount a filesystem over bar, getcwd returns a path which is not resolvable: quack:/tmp/foo/bar/baz # pwd /tmp/foo/bar/baz quack:/tmp/foo/bar/baz # cd /tmp/foo/bar/baz bash: cd: /tmp/foo/bar/baz: No such file or directory So you can do rather insane stuff with directory tree under linux. Most admins don't but e.g. container guys do and linux dcache is designed to accomodate this which makes answering some otherwise simple questions rather complicated. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
