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Message-ID: <20200617181816.GA18315@fieldses.org> Date: Wed, 17 Jun 2020 14:18:16 -0400 From: "J. Bruce Fields" <bfields@...ldses.org> To: Eric Sandeen <sandeen@...deen.net> Cc: "Darrick J. Wong" <darrick.wong@...cle.com>, Christoph Hellwig <hch@...radead.org>, Masayoshi Mizuma <msys.mizuma@...il.com>, Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, Alexander Viro <viro@...iv.linux.org.uk>, Masayoshi Mizuma <m.mizuma@...fujitsu.com>, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-xfs <linux-xfs@...r.kernel.org> Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts On Wed, Jun 17, 2020 at 12:55:24PM -0500, Eric Sandeen wrote: > On 6/17/20 12:24 PM, Darrick J. Wong wrote: > > On Wed, Jun 17, 2020 at 12:14:28PM -0500, Eric Sandeen wrote: > >> > >> > >> On 6/17/20 10:58 AM, J. Bruce Fields wrote: > >>> On Wed, Jun 17, 2020 at 01:03:14AM -0700, Christoph Hellwig wrote: > >>>> On Tue, Jun 16, 2020 at 04:21:23PM -0400, Masayoshi Mizuma wrote: > >>>>> From: Masayoshi Mizuma <m.mizuma@...fujitsu.com> > >>>>> > >>>>> /proc/mounts doesn't show 'i_version' even if iversion > >>>>> mount option is set to XFS. > >>>>> > >>>>> iversion mount option is a VFS option, not ext4 specific option. > >>>>> Move the handler to show_sb_opts() so that /proc/mounts can show > >>>>> 'i_version' on not only ext4 but also the other filesystem. > >>>> > >>>> SB_I_VERSION is a kernel internal flag. XFS doesn't have an i_version > >>>> mount option. > >>> > >>> It probably *should* be a kernel internal flag, but it seems to work as > >>> a mount option too. > >> > >> Not on XFS AFAICT: > >> > >> [600280.685810] xfs: Unknown parameter 'i_version' > > > > Yeah, because the mount option is 'iversion', not 'i_version'. Even if > > unless you're ext4: > > {Opt_i_version, "i_version"}, > > ok "iversion" is what mount(8) takes and translates into MS_I_VERSION (thanks Darrick) > > # strace -vv -emount mount -oloop,iversion fsfile mnt > mount("/dev/loop0", "/tmp/mnt", "xfs", MS_I_VERSION, NULL) = 0 > > FWIW, mount actually seems to pass what it finds in /proc/mounts back in on remount for ext4: > > # strace -vv -emount mount -o remount mnt > mount("/dev/loop0", "/tmp/mnt", 0x55bfcbdca150, MS_REMOUNT|MS_RELATIME, "seclabel,i_version,data=ordered") = 0 > > but it still looks unhandled on remount. Perhaps if /proc/mounts exposed > "iversion" (not "i_version") then mount -o remount would DTRT. I'd rather just eliminate the option, to the extent possible. It was only ever a mount option since it caused a performance regression in some filesystems, but I *think* that was addressed by Jeff Layton's work (f02a9ad1f15d "fs: handle inode->i_version more efficiently"). XFS in particular is just using this flag to tell knfsd that it should use i_version. I don't think it was really intended for userspace to be able to turn this off. --b.
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