[PATCH v2] erofs: support STATX_DIOALIGN

[Hongbo Li]

Add support for STATX_DIOALIGN to erofs, so that direct I/O
alignment restrictions are exposed to userspace in a generic
way.

[Before]
```
./statx_test /mnt/erofs/testfile
statx(/mnt/erofs/testfile) = 0
dio mem align:0
dio offset align:0
```

[After]
```
./statx_test /mnt/erofs/testfile
statx(/mnt/erofs/testfile) = 0
dio mem align:512
dio offset align:512
```

Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>

---
v2:
  - Removing the non-bdev case for obtaining the bsize.

v1: https://lore.kernel.org/all/afe7b51b-b235-4ad5-80a5-16e0e61e149e@linux.alibaba.com/T/
---
 fs/erofs/inode.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 5f6439a63af7..7c1163e47cb7 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -342,6 +342,23 @@ int erofs_getattr(struct mnt_idmap *idmap, const struct path *path,
 	stat->attributes_mask |= (STATX_ATTR_COMPRESSED |
 				  STATX_ATTR_IMMUTABLE);
 
+	/*
+	 * Return the DIO alignment restrictions if requested.
+	 *
+	 * In erofs, STATX_DIOALIGN is not supported in ondemand mode and
+	 * the compressed file, so in these cases we report no DIO support.
+	 */
+	if ((request_mask & STATX_DIOALIGN) && S_ISREG(inode->i_mode)) {
+		stat->result_mask |= STATX_DIOALIGN;
+		if (!erofs_is_fscache_mode(inode->i_sb) &&
+			!erofs_inode_is_data_compressed(EROFS_I(inode)->datalayout)) {
+			struct block_device *bdev = inode->i_sb->s_bdev;
+
+			stat->dio_mem_align = bdev_logical_block_size(bdev);
+			stat->dio_offset_align = stat->dio_mem_align;
+		}
+	}
+
 	generic_fillattr(idmap, request_mask, inode, stat);
 	return 0;
 }
-- 
2.34.1