From: Theodore Ts'o Subject: Re: [PATCH 2/3] mke2fs: print extra information about existing ext2/3/4 file systems Date: Mon, 5 May 2014 10:44:23 -0400 Message-ID: <20140505144423.GG22287@thunk.org> References: <1399295044-24489-1-git-send-email-tytso@mit.edu> <1399295044-24489-2-git-send-email-tytso@mit.edu> <20140505140401.GD22287@thunk.org> <20140505142808.GF22287@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Ext4 Developers List , kzak@redhat.com, linux-fsdevel@vger.kernel.org To: =?utf-8?B?THVrw6HFoQ==?= Czerner Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, May 05, 2014 at 04:38:37PM +0200, Luk=C3=A1=C5=A1 Czerner wrote= : > > % ./misc/mke2fs -t ext4 /dev/sdc3 > > mke2fs 1.42.9 (4-Feb-2014) > > /dev/sdc3 contains a ext4 file system > > last mounted on /SOX-backups on Mon May 5 08:59:53 2014 > > Proceed anyway? (y,n)=20 > >=20 > > ... where this becomes a last-ditch saving through against the > > accidental wiping of the enterprise's Sarbanes-Oxley records. :-) > >=20 >=20 > Yep, it's really useful. I just was not sure what is this all about s= ince > there was not description and I was missing context from the other pa= tches. >=20 > But this makes me think that it would be very useful if blkid could > gather this information for other file system if possible :). This > might be very useful if we can get some overlap with other file > system with the information provided in superblock. Unfortunately, as far as I know, none of the other file systems currently save the location where the file system was last mounted. And to be honest, the way we do it in ext4 is a horrible hack (get out your barf bags!): static int ext4_file_open(struct inode * inode, struct file * filp) { struct super_block *sb =3D inode->i_sb; struct ext4_sb_info *sbi =3D EXT4_SB(inode->i_sb); struct vfsmount *mnt =3D filp->f_path.mnt; struct path path; char buf[64], *cp; if (unlikely(!(sbi->s_mount_flags & EXT4_MF_MNTDIR_SAMPLED) && !(sb->s_flags & MS_RDONLY))) { sbi->s_mount_flags |=3D EXT4_MF_MNTDIR_SAMPLED; /* * Sample where the filesystem has been mounted and * store it in the superblock for sysadmin convenience * when trying to sort through large numbers of block * devices or filesystem images. */ memset(buf, 0, sizeof(buf)); path.mnt =3D mnt; path.dentry =3D mnt->mnt_root; cp =3D d_path(&path, buf, sizeof(buf)); ... What we would need to do is file a feature request in the other file systems to save this information, and then add proper support for to pass this information from the VFS layer into the struct super_operations's mount function, which would be the proper, sane way to provide this functionality. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html