From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: btrfs and /proc/self/mountinfo Date: Mon, 13 Apr 2009 09:40:51 -0400 Message-ID: <1239630051.24841.12.camel@think.oraclecorp.com> References: <7b13a0f80904120735r41736455hb7e226ab8ad30bd7@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-btrfs@vger.kernel.org To: David Zeuthen Return-path: In-Reply-To: <7b13a0f80904120735r41736455hb7e226ab8ad30bd7@mail.gmail.com> List-ID: 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