On Mon, 12 Jan 2015, Karel Zak wrote: > Date: Mon, 12 Jan 2015 14:00:58 +0100 > From: Karel Zak <kzak@xxxxxxxxxx> > To: Lukáš Czerner <lczerner@xxxxxxxxxx> > Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>, Al Viro <viro@xxxxxxxxxxxxxxxxxx>, > Dexuan Cui <decui@xxxxxxxxxxxxx>, > "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, > 'linux-ext4' <linux-ext4@xxxxxxxxxxxxxxx> > Subject: Re: Can one file system be R/W mounted multiple times in Linux? > > On Fri, Jan 09, 2015 at 04:52:11PM +0100, Lukáš Czerner wrote: > > Now the question is, whether 'mount' can be a bit smarter than that > > and just mount the already existing block device instead of creating > > new one ? Karel ? > > Well, the question is how smart is too smart :-) And Al is right, problem > is in races. > > Anyway, I'd like to avoid complex FS specific code in mount(8). IMHO > it's FS driver responsibility to avoid (or support) FS sharing between > more block devices. > > BTW, for ext4 you can enable ETX4_FEATURE_INCOMPAT_MMP to protect > against multi-mount. > > Karel Hi Karel, that's not what I meant at all. Yes, things like MMP should help. But what I was suggesting was not FS specific. mount(8) could in case of '-o loop' look whether there is already a block device associated with the file and if so use it instead of creating new one. However this might race with device removal among other things and I am not sure whether there is any easy solution. Thanks! -Lukas
