From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01A4EC2BD09 for ; Tue, 2 Jul 2024 00:22:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6D7B26B0088; Mon, 1 Jul 2024 20:22:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 687896B008C; Mon, 1 Jul 2024 20:22:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4DA8E6B0092; Mon, 1 Jul 2024 20:22:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 2F5796B0088 for ; Mon, 1 Jul 2024 20:22:14 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id C0250C14CE for ; Tue, 2 Jul 2024 00:22:13 +0000 (UTC) X-FDA: 82292910546.01.5037C4D Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf28.hostedemail.com (Postfix) with ESMTP id E7834C0012 for ; Tue, 2 Jul 2024 00:22:11 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=IYYjhApb; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf28.hostedemail.com: domain of jlayton@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=jlayton@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1719879707; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=zDIIjNjDNZ+zeVd7ZnsACpW4CMz53sV86f9CxGcKU3c=; b=2uqH7Mf104WFokUQjZDrrxre0dtbSgIqIJuxYCi605qWFCLuMqynfOWTZuDKQEQD3ypSbD 1o68x+r7liGQWPP4kxFGEOcTj8N3LPLZ931c68dEDwPEB6ePQ+2XJLH5opx8BA/Ta5P+1/ F5bwlXw5NAvrNMkczT8I99vrLIp2rQU= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1719879707; a=rsa-sha256; cv=none; b=rcXI4zLTccaDa80IhZDP5kLxtZy9EFOj7/ZtHUiSv4t8g6KCEQJBIiROUwXNV8KjJ9VaOY ADeR4BFAc0tBW94n3b2BLxxIm2aKQlJP2jmRpaHc1eb+s4HZat2HZgpdDctbBlfaiHvGVV qyrhpSddBUhHFvkjsV1UmbjE5OcIiYE= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=IYYjhApb; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf28.hostedemail.com: domain of jlayton@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=jlayton@kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id A43E960AFD; Tue, 2 Jul 2024 00:22:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47C20C116B1; Tue, 2 Jul 2024 00:22:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719879730; bh=eilQUQR1hEY1n0+7vh9oO2ffjz4mLnCHXgoFHh9075A=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=IYYjhApbHDW/NxyC5Q3C1G5etBVbKHdmHFdwzcNJFv2Izbhy9mFkpPzBs7YgR3aum 1AaUcEHTDLbxEJPLHmrAYKyrUlW9eX7ZFQA5Wm6Ovs/EwwqwtSDDZbVv2g9t4vCdgP II/UQWgyLap2u/3qfpXg0xt7JFVPt1BqeBm4yGQl1IAXukM5aaRUY4v2SsphfUN41q ShisS2T+OJxZ8snKNBhLFzrVgwyGauII9kRgPWVkcHvS2BAUMpRaqSuHRLUSB6WzcZ YpmKvfjNaZO4Lg1yCO8wXW6pWvLBrVCvqH0fACgBeiC5euBZMq9WkvH7yV8tk/bOKy ubH5Qzu19+jGA== Message-ID: <3042db2f803fbc711575ec4f1c4a273912a50904.camel@kernel.org> Subject: Re: [PATCH 01/10] fs: turn inode ctime fields into a single ktime_t From: Jeff Layton To: "Darrick J. Wong" Cc: Alexander Viro , Christian Brauner , Jan Kara , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Chandan Babu R , Theodore Ts'o , Andreas Dilger , Chris Mason , Josef Bacik , David Sterba , Hugh Dickins , Andrew Morton , kernel-team@fb.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org Date: Mon, 01 Jul 2024 20:22:07 -0400 In-Reply-To: <20240701224941.GE612460@frogsfrogsfrogs> References: <20240626-mgtime-v1-0-a189352d0f8f@kernel.org> <20240626-mgtime-v1-1-a189352d0f8f@kernel.org> <20240701224941.GE612460@frogsfrogsfrogs> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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X-Rspamd-Queue-Id: E7834C0012 X-Stat-Signature: 7cs3qn4ncgnpopeif3c6dznyhjt43394 X-Rspam-User: X-HE-Tag: 1719879731-245161 X-HE-Meta: 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 qM6cvUNb 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Wong wrote: > On Wed, Jun 26, 2024 at 09:00:21PM -0400, Jeff Layton wrote: > > The ctime is not settable to arbitrary values. It always comes from the > > system clock, so we'll never stamp an inode with a value that can't be > > represented there. If we disregard people setting their system clock > > past the year 2262, there is no reason we can't replace the ctime field= s > > with a ktime_t. > >=20 > > Switch the ctime fields to a single ktime_t. Move the i_generation down > > above i_fsnotify_mask and then move the i_version into the resulting 8 > > byte hole. This shrinks struct inode by 8 bytes total, and should > > improve the cache footprint as the i_version and ctime are usually > > updated together. > >=20 > > The one downside I can see to switching to a ktime_t is that if someone > > has a filesystem with files on it that has ctimes outside the ktime_t > > range (before ~1678 AD or after ~2262 AD), we won't be able to display > > them properly in stat() without some special treatment in the > > filesystem. The operating assumption here is that that is not a > > practical problem. >=20 > What happens if a filesystem with the ability to store ctimes beyond > whatever ktime_t supports (AFAICT 2^63-1 nanonseconds on either side of > the Unix epoch)? I think the behavior with your patch is that ktime_set > clamps the ctime on iget because the kernel can't handle it? >=20 > It's a little surprising that the ctime will suddenly jump back in time > to 2262, but maybe you're right that nobody will notice or care? ;) >=20 >=20 Yeah, it'd be clamped at KTIME_MAX when we pull in the inode from disk, a'la ktime_set. I think it's important to note that the ctime is not settable from userland, so if an on-disk ctime is outside of the ktime_t range, there are only two possibilities: 1) the system clock was set to some time (far) in the future when the file's metadata was last altered (bad clock? time traveling fs?). ...or... 2) the filesystem has been altered (fuzzing? deliberate doctoring?). None of these seem like legitimate use cases so I'm arguing that we shouldn't worry about them. (...ok maybe the time travel one could be legit, but someone needs to step up and make a case for it, if so.) > >=20 > > Signed-off-by: Jeff Layton > > --- > > include/linux/fs.h | 26 +++++++++++--------------- > > 1 file changed, 11 insertions(+), 15 deletions(-) > >=20 > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > index 5ff362277834..5139dec085f2 100644 > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -662,11 +662,10 @@ struct inode { > > loff_t i_size; > > time64_t i_atime_sec; > > time64_t i_mtime_sec; > > - time64_t i_ctime_sec; > > u32 i_atime_nsec; > > u32 i_mtime_nsec; > > - u32 i_ctime_nsec; > > - u32 i_generation; > > + ktime_t __i_ctime; > > + atomic64_t i_version; > > spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */ > > unsigned short i_bytes; > > u8 i_blkbits; > > @@ -701,7 +700,6 @@ struct inode { > > struct hlist_head i_dentry; > > struct rcu_head i_rcu; > > }; > > - atomic64_t i_version; > > atomic64_t i_sequence; /* see futex */ > > atomic_t i_count; > > atomic_t i_dio_count; > > @@ -724,6 +722,8 @@ struct inode { > > }; > > =20 > > =20 > > + u32 i_generation; > > + > > #ifdef CONFIG_FSNOTIFY > > __u32 i_fsnotify_mask; /* all events this inode cares about */ > > /* 32-bit hole reserved for expanding i_fsnotify_mask */ > > @@ -1608,29 +1608,25 @@ static inline struct timespec64 inode_set_mtime= (struct inode *inode, > > return inode_set_mtime_to_ts(inode, ts); > > } > > =20 > > -static inline time64_t inode_get_ctime_sec(const struct inode *inode) > > +static inline struct timespec64 inode_get_ctime(const struct inode *in= ode) > > { > > - return inode->i_ctime_sec; > > + return ktime_to_timespec64(inode->__i_ctime); > > } > > =20 > > -static inline long inode_get_ctime_nsec(const struct inode *inode) > > +static inline time64_t inode_get_ctime_sec(const struct inode *inode) > > { > > - return inode->i_ctime_nsec; > > + return inode_get_ctime(inode).tv_sec; > > } > > =20 > > -static inline struct timespec64 inode_get_ctime(const struct inode *in= ode) > > +static inline long inode_get_ctime_nsec(const struct inode *inode) > > { > > - struct timespec64 ts =3D { .tv_sec =3D inode_get_ctime_sec(inode), > > - .tv_nsec =3D inode_get_ctime_nsec(inode) }; > > - > > - return ts; > > + return inode_get_ctime(inode).tv_nsec; > > } > > =20 > > static inline struct timespec64 inode_set_ctime_to_ts(struct inode *in= ode, > > struct timespec64 ts) > > { > > - inode->i_ctime_sec =3D ts.tv_sec; > > - inode->i_ctime_nsec =3D ts.tv_nsec; > > + inode->__i_ctime =3D ktime_set(ts.tv_sec, ts.tv_nsec); > > return ts; > > } > > =20 > >=20 > > --=20 > > 2.45.2 > >=20 > >=20 --=20 Jeff Layton