On 27/10/2024 18:17, 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;
+}
+
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)) {
+ 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..d6e3201a48be 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))
this check is duplicated, since bdev_atomic_write_unit_{min,
max}_bytes() has this check
+ 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) {
This looks a bit complicated. I would just follow the XFS example and
ensure bdev_atomic_write_unit_min_bytes() <= sb->s_blocksize <=
bdev_atomic_write_unit_max_bytes() [which you are doing, but in a
complicated way]
+ ext4_msg(sb, KERN_NOTICE, "Supports 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;
