Re: [PATCH V1 7/9] fs/ext4: Make DAX mount option a tri-state

Darrick J. Wong
2020-05-14T15:11:13Z

On Wed, May 13, 2020 at 11:53:13PM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> We add 'always', 'never', and 'inode' (default). '-o dax' continue to
> operate the same.
>
> Specifically we introduce a 2nd DAX mount flag EXT4_MOUNT2_DAX_NEVER and set
> it and EXT4_MOUNT_DAX_ALWAYS appropriately.
>
> We also force EXT4_MOUNT2_DAX_NEVER if !CONFIG_FS_DAX.
>
> https://lore.kernel.org/lkml/20200405061945.GA94792@iweiny-DESK2.sc.intel.com/
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> Changes from RFC:
> Combine remount check for DAX_NEVER with DAX_ALWAYS
> Update ext4_should_enable_dax()
> ---
> fs/ext4/ext4.h | 1 +
> fs/ext4/inode.c | 2 ++
> fs/ext4/super.c | 43 +++++++++++++++++++++++++++++++++++++------
> 3 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 86a0994332ce..01d1de838896 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1168,6 +1168,7 @@ 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_EXPLICIT_JOURNAL_CHECKSUM 0x00000008 /* User explicitly
> specified journal checksum */
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 23e42a223235..140b1930e2f4 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4400,6 +4400,8 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
>
> static bool ext4_should_enable_dax(struct inode *inode)
> {
> + 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 5ec900fdf73c..e01a040a58a9 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1505,6 +1505,7 @@ enum {
> 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_dax_str,
> 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,
> @@ -1570,6 +1571,7 @@ static const match_table_t tokens = {
> {Opt_barrier, "barrier"},
> {Opt_nobarrier, "nobarrier"},
> {Opt_i_version, "i_version"},
> + {Opt_dax_str, "dax=%s"},
> {Opt_dax, "dax"},
> {Opt_stripe, "stripe=%u"},
> {Opt_delalloc, "delalloc"},
> @@ -1767,6 +1769,7 @@ 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_str, 0, MOPT_STRING},
> {Opt_dax, EXT4_MOUNT_DAX_ALWAYS, MOPT_SET},
> {Opt_stripe, 0, MOPT_GTE0},
> {Opt_resuid, 0, MOPT_GTE0},
> @@ -2076,13 +2079,32 @@ 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_str) {
> #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;
> + char *tmp = match_strdup(&args[0]);
> +
> + if (!tmp || !strcmp(tmp, "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;
> + } else if (!strcmp(tmp, "never")) {
> + sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
> + sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
> + } else if (!strcmp(tmp, "inode")) {
> + sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
> + sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER;
> + } else {
> + ext4_msg(sb, KERN_WARNING, "DAX invalid option.");
> + kfree(tmp);
> + return -1;
> + }
> +
> + kfree(tmp);
> #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
> } else if (token == Opt_data_err_abort) {
> @@ -2306,6 +2328,13 @@ 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_opt2(sb, DAX_NEVER))
> + SEQ_OPTS_PUTS("dax=never");
> + else if (test_opt(sb, DAX_ALWAYS))
> + SEQ_OPTS_PUTS("dax=always");
> + else
> + SEQ_OPTS_PUTS("dax=inode");

dax=inode is the default; do you need to show it?

(Especially since xfs doesn't...)

--D

> +
> ext4_show_quota_options(seq, sb);
> return 0;
> }
> @@ -5425,10 +5454,12 @@ 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) {
> ext4_msg(sb, KERN_WARNING, "warning: refusing change of "
> - "dax flag with busy inodes while remounting");
> + "dax mount option with busy inodes while remounting");
> sbi->s_mount_opt ^= EXT4_MOUNT_DAX_ALWAYS;
> + sbi->s_mount_opt2 ^= EXT4_MOUNT2_DAX_NEVER;
> }
>
> if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)
> --
> 2.25.1
>