[PATCH v3] erofs: support STATX_DIOALIGN

[Gao Xiang <hsiangkao@linux.alibaba.com>]

From: Hongbo Li via Linux-erofs <linux-erofs@lists.ozlabs.org>

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@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
Hi Hongbo,

I tidy up the patch a bit according to the current codebase,
I will apply this later for this cycle.

Also r-v-bs are always welcome...

Thanks,
Gao Xiang

 fs/erofs/inode.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 5f6439a63af7..43c09aae2afc 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -334,14 +334,29 @@ int erofs_getattr(struct mnt_idmap *idmap, const struct path *path,
 		  unsigned int query_flags)
 {
 	struct inode *const inode = d_inode(path->dentry);
+	bool compressed =
+		erofs_inode_is_data_compressed(EROFS_I(inode)->datalayout);
 
-	if (erofs_inode_is_data_compressed(EROFS_I(inode)->datalayout))
+	if (compressed)
 		stat->attributes |= STATX_ATTR_COMPRESSED;
-
 	stat->attributes |= STATX_ATTR_IMMUTABLE;
 	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
+	 * compressed files, 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) && !compressed) {
+			stat->dio_mem_align =
+				bdev_logical_block_size(inode->i_sb->s_bdev);
+			stat->dio_offset_align = stat->dio_mem_align;
+		}
+	}
 	generic_fillattr(idmap, request_mask, inode, stat);
 	return 0;
 }
-- 
2.43.5