ext4: Add statx support for atomic writes

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@linux.ibm.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 44b0d418143c2e36a55ba857be3f383643c31121..494d443e9fc99607eeae881318151e6990b72e5a 100644 (file)
--- 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 +3859,12 @@ static inline int ext4_buffer_uptodate(struct buffer_head *bh)
        return buffer_uptodate(bh);
 }
 
+static inline bool ext4_inode_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 54bdd4884fe67d4462c13751ffe723d78295a788..3e827cfa762e458239267ef4a4a5131484e84ac8 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5578,6 +5578,18 @@ int ext4_getattr(struct mnt_idmap *idmap, const struct path *path,
                }
        }
 
+       if ((request_mask & STATX_WRITE_ATOMIC) && S_ISREG(inode->i_mode)) {
+               struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+               unsigned int awu_min = 0, awu_max = 0;
+
+               if (ext4_inode_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);
+       }
+
        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 16a4ce704460e141cebba38b88513221ca16461e..ebe1660bd840ae43d371c55790ea19aaef911f7e 100644 (file)
--- 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;