Date: Fri, 21 Jun 2024 12:07:43 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: chandan.babu@...cle.com, dchinner@...hat.com, hch@....de,
	viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, catherine.hoang@...cle.com,
	martin.petersen@...cle.com
Subject: Re: [PATCH 07/13] xfs: Introduce FORCEALIGN inode flag

On Fri, Jun 21, 2024 at 10:05:34AM +0000, John Garry wrote:
> From: "Darrick J. Wong" <djwong@...nel.org>
> 
> Add a new inode flag to require that all file data extent mappings must
> be aligned (both the file offset range and the allocated space itself)
> to the extent size hint.  Having a separate COW extent size hint is no
> longer allowed.

It might be worth mentioning that for non-rt files, the allocated space
will be aligned to the start of an AG, not necessary the block device,
though the upcoming atomicwrites inode flag will also require that.

Also this should clarify what happens for rt files -- do we allow
forcealign realtime files?  Or only for the sb_rextsize == 1 case?
Or for any sbrextsize?

> The goal here is to enable sysadmins and users to mandate that all space
> mappings in a file must have a startoff/blockcount that are aligned to
> (say) a 2MB alignment and that the startblock/blockcount will follow the
> same alignment.
> 
> Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
> Co-developed-by: John Garry <john.g.garry@...cle.com>
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/xfs/libxfs/xfs_format.h    |  6 +++-
>  fs/xfs/libxfs/xfs_inode_buf.c | 53 +++++++++++++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_inode_buf.h |  3 ++
>  fs/xfs/libxfs/xfs_sb.c        |  2 ++
>  fs/xfs/xfs_inode.c            | 13 +++++++++
>  fs/xfs/xfs_inode.h            | 20 ++++++++++++-
>  fs/xfs/xfs_ioctl.c            | 47 +++++++++++++++++++++++++++++--
>  fs/xfs/xfs_mount.h            |  2 ++
>  fs/xfs/xfs_reflink.h          | 10 -------
>  fs/xfs/xfs_super.c            |  4 +++
>  include/uapi/linux/fs.h       |  2 ++
>  11 files changed, 148 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index 61f51becff4f..b48cd75d34a6 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -353,6 +353,7 @@ xfs_sb_has_compat_feature(
>  #define XFS_SB_FEAT_RO_COMPAT_RMAPBT   (1 << 1)		/* reverse map btree */
>  #define XFS_SB_FEAT_RO_COMPAT_REFLINK  (1 << 2)		/* reflinked files */
>  #define XFS_SB_FEAT_RO_COMPAT_INOBTCNT (1 << 3)		/* inobt block counts */
> +#define XFS_SB_FEAT_RO_COMPAT_FORCEALIGN (1 << 30)	/* aligned file data extents */
>  #define XFS_SB_FEAT_RO_COMPAT_ALL \
>  		(XFS_SB_FEAT_RO_COMPAT_FINOBT | \
>  		 XFS_SB_FEAT_RO_COMPAT_RMAPBT | \
> @@ -1094,16 +1095,19 @@ static inline void xfs_dinode_put_rdev(struct xfs_dinode *dip, xfs_dev_t rdev)
>  #define XFS_DIFLAG2_COWEXTSIZE_BIT   2  /* copy on write extent size hint */
>  #define XFS_DIFLAG2_BIGTIME_BIT	3	/* big timestamps */
>  #define XFS_DIFLAG2_NREXT64_BIT 4	/* large extent counters */
> +/* data extent mappings for regular files must be aligned to extent size hint */
> +#define XFS_DIFLAG2_FORCEALIGN_BIT 5
>  
>  #define XFS_DIFLAG2_DAX		(1 << XFS_DIFLAG2_DAX_BIT)
>  #define XFS_DIFLAG2_REFLINK     (1 << XFS_DIFLAG2_REFLINK_BIT)
>  #define XFS_DIFLAG2_COWEXTSIZE  (1 << XFS_DIFLAG2_COWEXTSIZE_BIT)
>  #define XFS_DIFLAG2_BIGTIME	(1 << XFS_DIFLAG2_BIGTIME_BIT)
>  #define XFS_DIFLAG2_NREXT64	(1 << XFS_DIFLAG2_NREXT64_BIT)
> +#define XFS_DIFLAG2_FORCEALIGN	(1 << XFS_DIFLAG2_FORCEALIGN_BIT)
>  
>  #define XFS_DIFLAG2_ANY \
>  	(XFS_DIFLAG2_DAX | XFS_DIFLAG2_REFLINK | XFS_DIFLAG2_COWEXTSIZE | \
> -	 XFS_DIFLAG2_BIGTIME | XFS_DIFLAG2_NREXT64)
> +	 XFS_DIFLAG2_BIGTIME | XFS_DIFLAG2_NREXT64 | XFS_DIFLAG2_FORCEALIGN)
>  
>  static inline bool xfs_dinode_has_bigtime(const struct xfs_dinode *dip)
>  {
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> index e7a7bfbe75b4..b2c5f466c1a9 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -644,6 +644,15 @@ xfs_dinode_verify(
>  	    !xfs_has_bigtime(mp))
>  		return __this_address;
>  
> +	if (flags2 & XFS_DIFLAG2_FORCEALIGN) {
> +		fa = xfs_inode_validate_forcealign(mp,
> +			be32_to_cpu(dip->di_extsize),
> +			be32_to_cpu(dip->di_cowextsize),
> +			mode, flags, flags2);

Needs another level of indent.

		fa = xfs_inode_validate_forcealign(mp,
				be32_to_cpu(dip->di_extsize),
				be32_to_cpu(dip->di_cowextsize),
				mode, flags, flags2);

> +		if (fa)
> +			return fa;
> +	}
> +
>  	return NULL;
>  }
>  
> @@ -811,3 +820,47 @@ xfs_inode_validate_cowextsize(
>  
>  	return NULL;
>  }
> +
> +/* Validate the forcealign inode flag */
> +xfs_failaddr_t
> +xfs_inode_validate_forcealign(
> +	struct xfs_mount	*mp,
> +	uint32_t		extsize,
> +	uint32_t		cowextsize,
> +	uint16_t		mode,
> +	uint16_t		flags,
> +	uint64_t		flags2)
> +{
> +	/* superblock rocompat feature flag */
> +	if (!xfs_has_forcealign(mp))
> +		return __this_address;
> +
> +	/* Only regular files and directories */
> +	if (!S_ISDIR(mode) && !S_ISREG(mode))
> +		return __this_address;
> +
> +	/* We require EXTSIZE or EXTSZINHERIT */
> +	if (!(flags & (XFS_DIFLAG_EXTSIZE | XFS_DIFLAG_EXTSZINHERIT)))
> +		return __this_address;
> +
> +	/* We require a non-zero extsize */
> +	if (!extsize)
> +		return __this_address;
> +
> +	/* Reflink'ed disallowed */
> +	if (flags2 & XFS_DIFLAG2_REFLINK)
> +		return __this_address;

This is still a significant limitation to end up encoding in the ondisk
format.  Given that we may some day fix that limitation by teaching
pagecache writeback how to do writeback on entire allocation units,
I think for now you should refuse to mount any filesystem with reflink
and forcealign enabled at the same time.

> +
> +	/* COW extsize disallowed */
> +	if (flags2 & XFS_DIFLAG2_COWEXTSIZE)
> +		return __this_address;
> +
> +	if (cowextsize)
> +		return __this_address;
> +
> +	/* A RT device with sb_rextsize=1 could make use of forcealign */
> +	if (flags & XFS_DIFLAG_REALTIME && mp->m_sb.sb_rextsize != 1)
> +		return __this_address;

Ok, so forcealign and bigrtalloc are not compatible?  I would have
thought they would be ok together since the rest of your code changes
short circuit into the forcealign case before the bigrtalloc case.
All you need here is to validate that i_extsize % sb_rextsize == 0.

> +
> +	return NULL;

You don't check that i_extsize % sb_agblocks == 0 for non-rt files
because that is only required for atomic writes + forcealign, right?

> +}
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.h b/fs/xfs/libxfs/xfs_inode_buf.h
> index 585ed5a110af..b8b65287b037 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.h
> +++ b/fs/xfs/libxfs/xfs_inode_buf.h
> @@ -33,6 +33,9 @@ xfs_failaddr_t xfs_inode_validate_extsize(struct xfs_mount *mp,
>  xfs_failaddr_t xfs_inode_validate_cowextsize(struct xfs_mount *mp,
>  		uint32_t cowextsize, uint16_t mode, uint16_t flags,
>  		uint64_t flags2);
> +xfs_failaddr_t xfs_inode_validate_forcealign(struct xfs_mount *mp,
> +		uint32_t extsize, uint32_t cowextsize, uint16_t mode,
> +		uint16_t flags, uint64_t flags2);
>  
>  static inline uint64_t xfs_inode_encode_bigtime(struct timespec64 tv)
>  {
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index 6b56f0f6d4c1..e56911553edd 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -164,6 +164,8 @@ xfs_sb_version_to_features(
>  		features |= XFS_FEAT_REFLINK;
>  	if (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_INOBTCNT)
>  		features |= XFS_FEAT_INOBTCNT;
> +	if (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_FORCEALIGN)
> +		features |= XFS_FEAT_FORCEALIGN;
>  	if (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_FTYPE)
>  		features |= XFS_FEAT_FTYPE;
>  	if (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_SPINODES)
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index f36091e1e7f5..994fb7e184d9 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -608,6 +608,8 @@ xfs_ip2xflags(
>  			flags |= FS_XFLAG_DAX;
>  		if (ip->i_diflags2 & XFS_DIFLAG2_COWEXTSIZE)
>  			flags |= FS_XFLAG_COWEXTSIZE;
> +		if (ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN)
> +			flags |= FS_XFLAG_FORCEALIGN;
>  	}
>  
>  	if (xfs_inode_has_attr_fork(ip))
> @@ -737,6 +739,8 @@ xfs_inode_inherit_flags2(
>  	}
>  	if (pip->i_diflags2 & XFS_DIFLAG2_DAX)
>  		ip->i_diflags2 |= XFS_DIFLAG2_DAX;
> +	if (pip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN)
> +		ip->i_diflags2 |= XFS_DIFLAG2_FORCEALIGN;
>  
>  	/* Don't let invalid cowextsize hints propagate. */
>  	failaddr = xfs_inode_validate_cowextsize(ip->i_mount, ip->i_cowextsize,
> @@ -745,6 +749,15 @@ xfs_inode_inherit_flags2(
>  		ip->i_diflags2 &= ~XFS_DIFLAG2_COWEXTSIZE;
>  		ip->i_cowextsize = 0;
>  	}
> +
> +	if (ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN) {
> +		failaddr = xfs_inode_validate_forcealign(ip->i_mount,
> +				ip->i_extsize, ip->i_cowextsize,
> +				VFS_I(ip)->i_mode, ip->i_diflags,
> +				ip->i_diflags2);
> +		if (failaddr)
> +			ip->i_diflags2 &= ~XFS_DIFLAG2_FORCEALIGN;
> +	}
>  }
>  
>  /*
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 42f999c1106c..536e646dd055 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -301,6 +301,16 @@ static inline bool xfs_inode_has_cow_data(struct xfs_inode *ip)
>  	return ip->i_cowfp && ip->i_cowfp->if_bytes;
>  }
>  
> +static inline bool xfs_is_always_cow_inode(struct xfs_inode *ip)
> +{
> +	return ip->i_mount->m_always_cow && xfs_has_reflink(ip->i_mount);
> +}
> +
> +static inline bool xfs_is_cow_inode(struct xfs_inode *ip)
> +{
> +	return xfs_is_reflink_inode(ip) || xfs_is_always_cow_inode(ip);
> +}
> +
>  static inline bool xfs_inode_has_bigtime(struct xfs_inode *ip)
>  {
>  	return ip->i_diflags2 & XFS_DIFLAG2_BIGTIME;
> @@ -313,7 +323,15 @@ static inline bool xfs_inode_has_large_extent_counts(struct xfs_inode *ip)
>  
>  static inline bool xfs_inode_has_forcealign(struct xfs_inode *ip)
>  {
> -	return false;
> +	if (!(ip->i_diflags & XFS_DIFLAG_EXTSIZE))
> +		return false;
> +	if (ip->i_extsize <= 1)
> +		return false;
> +	if (xfs_is_cow_inode(ip))
> +		return false;
> +	if (ip->i_diflags & XFS_DIFLAG_REALTIME)
> +		return false;
> +	return ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN;

In theory we already validated all of these fields when we loaded the
inode, right?  In which case you only need to check diflags2.

>  }
>  
>  /*
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index f0117188f302..5eff8fd9fa3e 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -525,10 +525,48 @@ xfs_flags2diflags2(
>  		di_flags2 |= XFS_DIFLAG2_DAX;
>  	if (xflags & FS_XFLAG_COWEXTSIZE)
>  		di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
> +	if (xflags & FS_XFLAG_FORCEALIGN)
> +		di_flags2 |= XFS_DIFLAG2_FORCEALIGN;
>  
>  	return di_flags2;
>  }
>  
> +/*
> + * Forcealign requires a non-zero extent size hint and a zero cow
> + * extent size hint.  Don't allow set for RT files yet.
> + */
> +static int
> +xfs_ioctl_setattr_forcealign(
> +	struct xfs_inode	*ip,
> +	struct fileattr		*fa)
> +{
> +	struct xfs_mount	*mp = ip->i_mount;
> +
> +	if (!xfs_has_forcealign(mp))
> +		return -EINVAL;
> +
> +	if (xfs_is_reflink_inode(ip))
> +		return -EINVAL;
> +
> +	if (!(fa->fsx_xflags & (FS_XFLAG_EXTSIZE |
> +				FS_XFLAG_EXTSZINHERIT)))
> +		return -EINVAL;
> +
> +	if (fa->fsx_xflags & FS_XFLAG_COWEXTSIZE)
> +		return -EINVAL;
> +
> +	if (!fa->fsx_extsize)
> +		return -EINVAL;
> +
> +	if (fa->fsx_cowextsize)
> +		return -EINVAL;
> +
> +	if (fa->fsx_xflags & FS_XFLAG_REALTIME)
> +		return -EINVAL;

The inode verifier allows realtime files so long as sb_rextsize is
nonzero.

> +
> +	return 0;
> +}
> +
>  static int
>  xfs_ioctl_setattr_xflags(
>  	struct xfs_trans	*tp,
> @@ -537,10 +575,12 @@ xfs_ioctl_setattr_xflags(
>  {
>  	struct xfs_mount	*mp = ip->i_mount;
>  	bool			rtflag = (fa->fsx_xflags & FS_XFLAG_REALTIME);
> +	bool			forcealign = fa->fsx_xflags & FS_XFLAG_FORCEALIGN;
>  	uint64_t		i_flags2;
>  
> -	if (rtflag != XFS_IS_REALTIME_INODE(ip)) {
> -		/* Can't change realtime flag if any extents are allocated. */
> +	/* Can't change RT or forcealign flags if any extents are allocated. */
> +	if (rtflag != XFS_IS_REALTIME_INODE(ip) ||
> +	    forcealign != xfs_inode_has_forcealign(ip)) {
>  		if (ip->i_df.if_nextents || ip->i_delayed_blks)
>  			return -EINVAL;
>  	}
> @@ -561,6 +601,9 @@ xfs_ioctl_setattr_xflags(
>  	if (i_flags2 && !xfs_has_v3inodes(mp))
>  		return -EINVAL;
>  
> +	if (forcealign && (xfs_ioctl_setattr_forcealign(ip, fa) < 0))
> +		return -EINVAL;

Either make xfs_ioctl_setattr_forcealign return a boolean, or extract
the error code and return that; don't just squash
xfs_ioctl_setattr_forcealign's negative errno into -EINVAL.

> +
>  	ip->i_diflags = xfs_flags2diflags(ip, fa->fsx_xflags);
>  	ip->i_diflags2 = i_flags2;
>  
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index d0567dfbc036..30228fea908d 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -299,6 +299,7 @@ typedef struct xfs_mount {
>  #define XFS_FEAT_NEEDSREPAIR	(1ULL << 25)	/* needs xfs_repair */
>  #define XFS_FEAT_NREXT64	(1ULL << 26)	/* large extent counters */
>  #define XFS_FEAT_EXCHANGE_RANGE	(1ULL << 27)	/* exchange range */
> +#define XFS_FEAT_FORCEALIGN	(1ULL << 28)	/* aligned file data extents */
>  
>  /* Mount features */
>  #define XFS_FEAT_NOATTR2	(1ULL << 48)	/* disable attr2 creation */
> @@ -385,6 +386,7 @@ __XFS_ADD_V4_FEAT(projid32, PROJID32)
>  __XFS_HAS_V4_FEAT(v3inodes, V3INODES)
>  __XFS_HAS_V4_FEAT(crc, CRC)
>  __XFS_HAS_V4_FEAT(pquotino, PQUOTINO)
> +__XFS_HAS_FEAT(forcealign, FORCEALIGN)
>  
>  /*
>   * Mount features
> diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
> index 65c5dfe17ecf..fb55e4ce49fa 100644
> --- a/fs/xfs/xfs_reflink.h
> +++ b/fs/xfs/xfs_reflink.h
> @@ -6,16 +6,6 @@
>  #ifndef __XFS_REFLINK_H
>  #define __XFS_REFLINK_H 1
>  
> -static inline bool xfs_is_always_cow_inode(struct xfs_inode *ip)
> -{
> -	return ip->i_mount->m_always_cow && xfs_has_reflink(ip->i_mount);
> -}
> -
> -static inline bool xfs_is_cow_inode(struct xfs_inode *ip)
> -{
> -	return xfs_is_reflink_inode(ip) || xfs_is_always_cow_inode(ip);
> -}
> -
>  extern int xfs_reflink_trim_around_shared(struct xfs_inode *ip,
>  		struct xfs_bmbt_irec *irec, bool *shared);
>  int xfs_bmap_trim_cow(struct xfs_inode *ip, struct xfs_bmbt_irec *imap,
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 27e9f749c4c7..852bbfb21506 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1721,6 +1721,10 @@ xfs_fs_fill_super(
>  		mp->m_features &= ~XFS_FEAT_DISCARD;
>  	}
>  
> +	if (xfs_has_forcealign(mp))
> +		xfs_warn(mp,
> +"EXPERIMENTAL forced data extent alignment feature in use. Use at your own risk!");

Here would be the place to fail the mount if reflink is enabled.

--D

> +
>  	if (xfs_has_reflink(mp)) {
>  		if (mp->m_sb.sb_rblocks) {
>  			xfs_alert(mp,
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 45e4e64fd664..8af304c0e29a 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -158,6 +158,8 @@ struct fsxattr {
>  #define FS_XFLAG_FILESTREAM	0x00004000	/* use filestream allocator */
>  #define FS_XFLAG_DAX		0x00008000	/* use DAX for IO */
>  #define FS_XFLAG_COWEXTSIZE	0x00010000	/* CoW extent size allocator hint */
> +/* data extent mappings for regular files must be aligned to extent size hint */
> +#define FS_XFLAG_FORCEALIGN	0x00020000
>  #define FS_XFLAG_HASATTR	0x80000000	/* no DIFLAG for this	*/
>  
>  /* the read-only stuff doesn't really belong here, but any other place is
> -- 
> 2.31.1
> 
> 

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