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

Xiao Yang
2020-05-27T05:55:07Z

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)