Re: [PATCH V4 6/8] fs/ext4: Make DAX mount option a tri-state

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On 2020/5/22 3:13, ira.weiny@intel.com wrote:
> From: Ira Weiny<ira.weiny@intel.com>
> 
> We add 'always', 'never', and 'inode' (default).  '-o dax' continues to
> operate the same which is equivalent to 'always'.  This new
> functionality is limited to ext4 only.
> 
> Specifically we introduce a 2nd DAX mount flag EXT4_MOUNT2_DAX_NEVER and set
> it and EXT4_MOUNT_DAX_ALWAYS appropriately for the mode.
> 
> We also force EXT4_MOUNT2_DAX_NEVER if !CONFIG_FS_DAX.
> 
> Finally, EXT4_MOUNT2_DAX_INODE is used solely to detect if the user
> specified that option for printing.
Hi Ira,

I have two questions when reviewing this patch:
1) After doing mount with the same dax=inode option, ext4/xfs shows
differnt output(i.e. xfs doesn't print 'dax=inode'):
---------------------------------------------------
# mount -o dax=inode /dev/pmem0 /mnt/xfstests/test/
# mount | grep pmem0
/dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel,dax=inode)

# mount -odax=inode /dev/pmem1 /mnt/xfstests/scratch/
# mount | grep pmem1
/dev/pmem1 on /mnt/xfstests/scratch type xfs
(rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota)
----------------------------------------------------
Is this expected output? why don't unify the output?

2) Do mount without dax and mount with -odax=inode have the same behavior?
---------------------------------------------------
# mount /dev/pmem0 /mnt/xfstests/test/
# mount | grep pmem0
/dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel)
# umount /mnt/xfstests/test
# mount -odax=inode /dev/pmem0 /mnt/xfstests/test/
# mount | grep pmem0
/dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel,dax=inode
---------------------------------------------------

BTW: I focus on the support of per-file/directory DAX operations recently.

> 
> Reviewed-by: Jan Kara<jack@suse.cz>
> Signed-off-by: Ira Weiny<ira.weiny@intel.com>
> 
> ---
> Changes from V1:
> 	Fix up mounting options to only show an option if specified
> 	Fix remount to prevent dax changes
> 	Isolate behavior to ext4 only
> 
> Changes from RFC:
> 	Combine remount check for DAX_NEVER with DAX_ALWAYS
> 	Update ext4_should_enable_dax()
> ---
>   fs/ext4/ext4.h  |  2 ++
>   fs/ext4/inode.c |  2 ++
>   fs/ext4/super.c | 67 +++++++++++++++++++++++++++++++++++++++++--------
>   3 files changed, 61 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index f5291693ce6e..65ffb831b2b9 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1168,6 +1168,8 @@ struct ext4_inode_info {
>   						      blocks */
>   #define EXT4_MOUNT2_HURD_COMPAT		0x00000004 /* Support HURD-castrated
>   						      file systems */
> +#define EXT4_MOUNT2_DAX_NEVER		0x00000008 /* Do not allow Direct Access */
> +#define EXT4_MOUNT2_DAX_INODE		0x00000010 /* For printing options only */
> 
>   #define EXT4_MOUNT2_EXPLICIT_JOURNAL_CHECKSUM	0x00000008 /* User explicitly
>   						specified journal checksum */
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 01636cf5f322..68fac9289109 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4402,6 +4402,8 @@ static bool ext4_should_enable_dax(struct inode *inode)
>   {
>   	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> 
> +	if (test_opt2(inode->i_sb, DAX_NEVER))
> +		return false;
>   	if (!S_ISREG(inode->i_mode))
>   		return false;
>   	if (ext4_should_journal_data(inode))
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 80eb814c47eb..5e056aa20ce9 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1512,7 +1512,8 @@ enum {
>   	Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
>   	Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_jqfmt_vfsv1, Opt_quota,
>   	Opt_noquota, Opt_barrier, Opt_nobarrier, Opt_err,
> -	Opt_usrquota, Opt_grpquota, Opt_prjquota, Opt_i_version, Opt_dax,
> +	Opt_usrquota, Opt_grpquota, Opt_prjquota, Opt_i_version,
> +	Opt_dax, Opt_dax_always, Opt_dax_inode, Opt_dax_never,
>   	Opt_stripe, Opt_delalloc, Opt_nodelalloc, Opt_warn_on_error,
>   	Opt_nowarn_on_error, Opt_mblk_io_submit,
>   	Opt_lazytime, Opt_nolazytime, Opt_debug_want_extra_isize,
> @@ -1579,6 +1580,9 @@ static const match_table_t tokens = {
>   	{Opt_nobarrier, "nobarrier"},
>   	{Opt_i_version, "i_version"},
>   	{Opt_dax, "dax"},
> +	{Opt_dax_always, "dax=always"},
> +	{Opt_dax_inode, "dax=inode"},
> +	{Opt_dax_never, "dax=never"},
>   	{Opt_stripe, "stripe=%u"},
>   	{Opt_delalloc, "delalloc"},
>   	{Opt_warn_on_error, "warn_on_error"},
> @@ -1726,6 +1730,7 @@ static int clear_qf_name(struct super_block *sb, int qtype)
>   #define MOPT_NO_EXT3	0x0200
>   #define MOPT_EXT4_ONLY	(MOPT_NO_EXT2 | MOPT_NO_EXT3)
>   #define MOPT_STRING	0x0400
> +#define MOPT_SKIP	0x0800
> 
>   static const struct mount_opts {
>   	int	token;
> @@ -1775,7 +1780,13 @@ static const struct mount_opts {
>   	{Opt_min_batch_time, 0, MOPT_GTE0},
>   	{Opt_inode_readahead_blks, 0, MOPT_GTE0},
>   	{Opt_init_itable, 0, MOPT_GTE0},
> -	{Opt_dax, EXT4_MOUNT_DAX_ALWAYS, MOPT_SET},
> +	{Opt_dax, EXT4_MOUNT_DAX_ALWAYS, MOPT_SET | MOPT_SKIP},
> +	{Opt_dax_always, EXT4_MOUNT_DAX_ALWAYS,
> +		MOPT_EXT4_ONLY | MOPT_SET | MOPT_SKIP},
> +	{Opt_dax_inode, EXT4_MOUNT2_DAX_INODE,
> +		MOPT_EXT4_ONLY | MOPT_SET | MOPT_SKIP},
> +	{Opt_dax_never, EXT4_MOUNT2_DAX_NEVER,
> +		MOPT_EXT4_ONLY | MOPT_SET | MOPT_SKIP},
>   	{Opt_stripe, 0, MOPT_GTE0},
>   	{Opt_resuid, 0, MOPT_GTE0},
>   	{Opt_resgid, 0, MOPT_GTE0},
> @@ -2084,13 +2095,32 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
>   		}
>   		sbi->s_jquota_fmt = m->mount_opt;
>   #endif
> -	} else if (token == Opt_dax) {
> +	} else if (token == Opt_dax || token == Opt_dax_always ||
> +		   token == Opt_dax_inode || token == Opt_dax_never) {
>   #ifdef CONFIG_FS_DAX
> -		ext4_msg(sb, KERN_WARNING,
> -		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
> -		sbi->s_mount_opt |= m->mount_opt;
> +		switch (token) {
> +		case Opt_dax:
> +		case Opt_dax_always:
> +			ext4_msg(sb, KERN_WARNING,
> +				"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
> +			sbi->s_mount_opt |= EXT4_MOUNT_DAX_ALWAYS;
> +			sbi->s_mount_opt2&= ~EXT4_MOUNT2_DAX_NEVER;
> +			break;
> +		case Opt_dax_never:
> +			sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
> +			sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
> +			break;
> +		case Opt_dax_inode:
> +			sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
> +			sbi->s_mount_opt2&= ~EXT4_MOUNT2_DAX_NEVER;
> +			/* Strictly for printing options */
> +			sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_INODE;
> +			break;
> +		}
>   #else
>   		ext4_msg(sb, KERN_INFO, "dax option not supported");
> +		sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
> +		sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
>   		return -1;
>   #endif

For s_mount_opt/s_mount_opt2, could we make the code more readable by
using set_opt()/set_opt2()/clear_opt()/clear_opt2() macros?

Thanks,
Xiao Yang
>   	} else if (token == Opt_data_err_abort) {
> @@ -2254,7 +2284,7 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
>   	for (m = ext4_mount_opts; m->token != Opt_err; m++) {
>   		int want_set = m->flags&  MOPT_SET;
>   		if (((m->flags&  (MOPT_SET|MOPT_CLEAR)) == 0) ||
> -		    (m->flags&  MOPT_CLEAR_ERR))
> +		    (m->flags&  MOPT_CLEAR_ERR) || m->flags&  MOPT_SKIP)
>   			continue;
>   		if (!nodefs&&  !(m->mount_opt&  (sbi->s_mount_opt ^ def_mount_opt)))
>   			continue; /* skip if same as the default */
> @@ -2314,6 +2344,17 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
>   	if (DUMMY_ENCRYPTION_ENABLED(sbi))
>   		SEQ_OPTS_PUTS("test_dummy_encryption");
> 
> +	if (test_opt(sb, DAX_ALWAYS)) {
> +		if (IS_EXT2_SB(sb))
> +			SEQ_OPTS_PUTS("dax");
> +		else
> +			SEQ_OPTS_PUTS("dax=always");
> +	} else if (test_opt2(sb, DAX_NEVER)) {
> +		SEQ_OPTS_PUTS("dax=never");
> +	} else if (test_opt2(sb, DAX_INODE)) {
> +		SEQ_OPTS_PUTS("dax=inode");
> +	}
> +
>   	ext4_show_quota_options(seq, sb);
>   	return 0;
>   }
> @@ -5436,10 +5477,16 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>   		goto restore_opts;
>   	}
> 
> -	if ((sbi->s_mount_opt ^ old_opts.s_mount_opt)&  EXT4_MOUNT_DAX_ALWAYS) {
> +	if ((sbi->s_mount_opt ^ old_opts.s_mount_opt)&  EXT4_MOUNT_DAX_ALWAYS ||
> +	    (sbi->s_mount_opt2 ^ old_opts.s_mount_opt2)&  EXT4_MOUNT2_DAX_NEVER ||
> +	    (sbi->s_mount_opt2 ^ old_opts.s_mount_opt2)&  EXT4_MOUNT2_DAX_INODE) {
>   		ext4_msg(sb, KERN_WARNING, "warning: refusing change of "
> -			"dax flag with busy inodes while remounting");
> -		sbi->s_mount_opt ^= EXT4_MOUNT_DAX_ALWAYS;
> +			"dax mount option with busy inodes while remounting");
> +		sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
> +		sbi->s_mount_opt |= old_opts.s_mount_opt&  EXT4_MOUNT_DAX_ALWAYS;
> +		sbi->s_mount_opt2&= ~(EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE);
> +		sbi->s_mount_opt2 |= old_opts.s_mount_opt2&
> +				     (EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE);
>   	}
> 
>   	if (sbi->s_mount_flags&  EXT4_MF_FS_ABORTED)