On Wed, Oct 30, 2024 at 09:27:38PM +0530, Ritesh Harjani (IBM) wrote:
> This patch adds base support for atomic writes via statx getattr.
> On bs < ps systems, we can create FS with say bs of 16k. That means
> both atomic write min and max unit can be set to 16k for supporting
> atomic writes.
>
> Co-developed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
> ---
> fs/ext4/ext4.h | 9 +++++++++
> fs/ext4/inode.c | 14 ++++++++++++++
> fs/ext4/super.c | 31 +++++++++++++++++++++++++++++++
> 3 files changed, 54 insertions(+)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 44b0d418143c..6ee49aaacd2b 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1729,6 +1729,10 @@ struct ext4_sb_info {
> */
> struct work_struct s_sb_upd_work;
>
> + /* Atomic write unit values in bytes */
> + unsigned int s_awu_min;
> + unsigned int s_awu_max;
> +
> /* Ext4 fast commit sub transaction ID */
> atomic_t s_fc_subtid;
>
> @@ -3855,6 +3859,11 @@ static inline int ext4_buffer_uptodate(struct buffer_head *bh)
> return buffer_uptodate(bh);
> }
>
> +static inline bool ext4_can_atomic_write(struct super_block *sb)
> +{
> + return EXT4_SB(sb)->s_awu_min > 0;
Huh, I was expecting you to stick to passing in the struct inode,
and then you end up with:
static inline bool ext4_can_atomic_write(struct inode *inode)
{
return S_ISREG(inode->i_mode) &&
EXT4_SB(inode->i_sb)->s_awu_min > 0);
}
> +}
> +
> extern int ext4_block_write_begin(handle_t *handle, struct folio *folio,
> loff_t pos, unsigned len,
> get_block_t *get_block);
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 54bdd4884fe6..fcdee27b9aa2 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5578,6 +5578,20 @@ int ext4_getattr(struct mnt_idmap *idmap, const struct path *path,
> }
> }
>
> + if (S_ISREG(inode->i_mode) && (request_mask & STATX_WRITE_ATOMIC)) {
...and then the callsites become:
if (request_mask & STATX_WRITE_ATOMIC) {
unsigned int awu_min = 0, awu_max = 0;
if (ext4_can_atomic_write(inode)) {
awu_min = sbi->s_awu_min;
awu_max = sbi->s_awu_max;
}
generic_fill_statx_atomic_writes(stat, awu_min, awu_max);
}
(I forget, is it bad if statx to a directory returns STATX_WRITE_ATOMIC
even with awu_{min,max} set to zero?)
Other than that nit, this looks good to me.
--D
> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> + unsigned int awu_min, awu_max;
> +
> + if (ext4_can_atomic_write(inode->i_sb)) {
> + awu_min = sbi->s_awu_min;
> + awu_max = sbi->s_awu_max;
> + } else {
> + awu_min = awu_max = 0;
> + }
> +
> + generic_fill_statx_atomic_writes(stat, awu_min, awu_max);
> + }
> +
> flags = ei->i_flags & EXT4_FL_USER_VISIBLE;
> if (flags & EXT4_APPEND_FL)
> stat->attributes |= STATX_ATTR_APPEND;
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 16a4ce704460..ebe1660bd840 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4425,6 +4425,36 @@ static int ext4_handle_clustersize(struct super_block *sb)
> return 0;
> }
>
> +/*
> + * ext4_atomic_write_init: Initializes filesystem min & max atomic write units.
> + * @sb: super block
> + * TODO: Later add support for bigalloc
> + */
> +static void ext4_atomic_write_init(struct super_block *sb)
> +{
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct block_device *bdev = sb->s_bdev;
> +
> + if (!bdev_can_atomic_write(bdev))
> + return;
> +
> + if (!ext4_has_feature_extents(sb))
> + return;
> +
> + sbi->s_awu_min = max(sb->s_blocksize,
> + bdev_atomic_write_unit_min_bytes(bdev));
> + sbi->s_awu_max = min(sb->s_blocksize,
> + bdev_atomic_write_unit_max_bytes(bdev));
> + if (sbi->s_awu_min && sbi->s_awu_max &&
> + sbi->s_awu_min <= sbi->s_awu_max) {
> + ext4_msg(sb, KERN_NOTICE, "Supports (experimental) DIO atomic writes awu_min: %u, awu_max: %u",
> + sbi->s_awu_min, sbi->s_awu_max);
> + } else {
> + sbi->s_awu_min = 0;
> + sbi->s_awu_max = 0;
> + }
> +}
> +
> static void ext4_fast_commit_init(struct super_block *sb)
> {
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> @@ -5336,6 +5366,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>
> spin_lock_init(&sbi->s_bdev_wb_lock);
>
> + ext4_atomic_write_init(sb);
> ext4_fast_commit_init(sb);
>
> sb->s_root = NULL;
> --
> 2.46.0
>
>
