btrfs: enhance error messages for delalloc range failure

When running emulated write error tests like generic/475, we can hit
error messages like this:

 BTRFS error (device dm-12 state EA): run_delalloc_nocow failed, root=596 inode=264 start=1605632 len=73728: -5
 BTRFS error (device dm-12 state EA): failed to run delalloc range, root=596 ino=264 folio=1605632 submit_bitmap=0-7 start=1605632 len=73728: -5

Which is normally buried by direct IO error messages.

However above error messages are not enough to determine which is the
real range that caused the error.
Considering we can have multiple different extents in one delalloc
range (e.g. some COW extents along with some NOCOW extents), just
outputting the error at the end of run_delalloc_nocow() is not enough.

To enhance the error messages:

- Remove the rate limit on the existing error messages
  In the generic/475 example, most error messages are from direct IO,
  not really from the delalloc range.
  Considering how useful the delalloc range error messages are, we don't
  want they to be rate limited.

- Add extra @cur_offset output for cow_file_range()
- Add extra variable output for run_delalloc_nocow()
  This is especially important for run_delalloc_nocow(), as there
  are extra error paths where we can hit error without into
  nocow_one_range() nor fallback_to_cow().

- Add an error message for nocow_one_range()
  That's the missing part.
  For fallback_to_cow(), we have error message from cow_file_range()
  already.

- Constify the @len and @EnD local variables for nocow_one_range()
  This makes it much easier to make sure @len and @EnD are not modified
  at runtime.

Reviewed-by: Boris Burkov <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: adam900710

fs/btrfs/inode.c

@@ -1534,10 +1534,11 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 		btrfs_qgroup_free_data(inode, NULL, start + cur_alloc_size,
 				       end - start - cur_alloc_size + 1, NULL);
 	}
-	btrfs_err_rl(fs_info,
-		     "%s failed, root=%llu inode=%llu start=%llu len=%llu: %d",
-		     __func__, btrfs_root_id(inode->root),
-		     btrfs_ino(inode), orig_start, end + 1 - orig_start, ret);
+	btrfs_err(fs_info,
+		  "%s failed, root=%llu inode=%llu start=%llu len=%llu cur_offset=%llu cur_alloc_size=%llu: %d",
+		  __func__, btrfs_root_id(inode->root),
+		  btrfs_ino(inode), orig_start, end + 1 - orig_start,
+		  start, cur_alloc_size, ret);
 	return ret;
 }
 
@@ -1969,8 +1970,8 @@ static int nocow_one_range(struct btrfs_inode *inode, struct folio *locked_folio
 			   u64 file_pos, bool is_prealloc)
 {
 	struct btrfs_ordered_extent *ordered;
-	u64 len = nocow_args->file_extent.num_bytes;
-	u64 end = file_pos + len - 1;
+	const u64 len = nocow_args->file_extent.num_bytes;
+	const u64 end = file_pos + len - 1;
 	int ret = 0;
 
 	btrfs_lock_extent(&inode->io_tree, file_pos, end, cached);
@@ -2017,8 +2018,13 @@ static int nocow_one_range(struct btrfs_inode *inode, struct folio *locked_folio
 	 * We do not clear the folio Dirty flags because they are set and
 	 * cleaered by the caller.
 	 */
-	if (ret < 0)
+	if (ret < 0) {
 		btrfs_cleanup_ordered_extents(inode, file_pos, len);
+		btrfs_err(inode->root->fs_info,
+			  "%s failed, root=%lld inode=%llu start=%llu len=%llu: %d",
+			  __func__, btrfs_root_id(inode->root), btrfs_ino(inode),
+			  file_pos, len, ret);
+	}
 	return ret;
 }
 
@@ -2306,10 +2312,11 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 		btrfs_qgroup_free_data(inode, NULL, untouched_start, untouched_len, NULL);
 	}
 	btrfs_free_path(path);
-	btrfs_err_rl(fs_info,
-		     "%s failed, root=%llu inode=%llu start=%llu len=%llu: %d",
-		     __func__, btrfs_root_id(inode->root),
-		     btrfs_ino(inode), start, end + 1 - start, ret);
+	btrfs_err(fs_info,
+"%s failed, root=%llu inode=%llu start=%llu len=%llu cur_offset=%llu oe_cleanup=%llu oe_cleanup_len=%llu untouched_start=%llu untouched_len=%llu: %d",
+		  __func__, btrfs_root_id(inode->root), btrfs_ino(inode),
+		  start, end + 1 - start, cur_offset, oe_cleanup_start, oe_cleanup_len,
+		  untouched_start, untouched_len, ret);
 	return ret;
 }