Re: btrfs and /proc/self/mountinfo
On Sun, 2009-04-12 at 10:35 -0400, David Zeuthen wrote: Hi, I have a question about how btrfs is supposed to work with /proc/self/mountinfo. It appears that the dev_t isn't matching what one would expect when mounting a btrfs filesystem - here's /dev/sdb2 mounted at /media/usb-fedora # cat /proc/self/mountinfo |grep btrfs 17 19 0:19 / /media/usb-fedora rw,nosuid,nodev,relatime - btrfs /dev/sdb2 rw Yes, this is because I switched to an anonymous super to remove restrictions about which devices could be removed from a mounted filesystem. Today it is possible to do something like this: mkfs.ext3 /dev/sdb mkfs.ext3 /dev/sdc mount /dev/sdb /mnt mount /dev/sdc /mnt Which gives me this in mountinfo: 29 14 8:16 / /mnt rw - ext3 /dev/sdb rw,errors=continue,data=ordered 31 29 8:32 / /mnt rw - ext3 /dev/sdc rw,errors=continue,data=ordered So, applications can already see duplicate device entries for the same mount point. Do they deal with that today? I'm not sure I'll be able to get control over the dev_ts mountinfo spits out just for btrfs, but we can always float a patch. Otherwise, we'll have to use the sysfs goo Kay is working on. -chris -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: btrfs and /proc/self/mountinfo
On Sun, Apr 12, 2009 at 07:35, David Zeuthen zeut...@gmail.com wrote: But we'd still need some kind of way of having the kernel tell user space what devices are currently claimed by the btrfs filesystem instance (and we'd need notifications on changes too). Otherwise we don't have enough information for the desktop shell and partitioning programs to let the user know that /dev/sdb2 or /dev/sdc1 or whatever is currently claimed by the 0:19 btrfs mount at /media/fedora-usb. One idea is to have a pollable file, /proc/fs/btrfs/devs, that maps from the dev_t of the btrfs filesystem instance (as used in /proc/self/mountinfo) to the set of dev_t for block devices currently claimed? E.g. for the example above we'd have /proc/fs/btrfs/devs: 0:19 8:18 Btrfs used to export some information in /sys/fs/btrfs/, this is disabled for now. Maybe we can possibly make it export something like: $ tree /sys/fs/btrfs/ /sys/fs/btrfs/ |-- 969d1386-a002-4c28-94f2-47be23f344e4 | |-- ba1532f3-849b-400b-9c76-2c9aee126c52 | | |-- device - ../../../devices/.../block/sda/sda3 | | |-- attribute1 | | |-- ... | `-- 45645656-849b-400b-9c76-2c9aee126c52 | |-- device - ../../../devices/.../block/sdb/sdb3 | |-- attribute1 | `-- 645645686-a002-4c28-94f2-47be23f344e4 |-- ... So you could look for a device link at the subvolume devices? Or if that does not fit for some reason, we could also add a btrfs class, to export details about the subvolumes. Thanks, Kay -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
