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[v3,27/49] btrfs: extent_io: don't allow tree block to cross page boundary for subpage support

Message ID 20200930015539.48867-28-wqu@suse.com
State New, archived
Headers show
Series btrfs: add partial rw support for subpage sector size | expand

Commit Message

Qu Wenruo Sept. 30, 2020, 1:55 a.m. UTC
As a preparation for subpage sector size support (allowing filesystem
with sector size smaller than page size to be mounted) if the sector
size is smaller than page size, we don't allow tree block to be read if
it crosses 64K(*) boundary.

The 64K is selected because:
- We are only going to support 64K page size for subpage for now
- 64K is also the max node size btrfs supports

This ensures that, tree blocks are always contained in one page for a
system with 64K page size, which can greatly simplify the handling.

Or we need to do complex multi-page handling for tree blocks.

Currently the only way to create such tree blocks crossing 64K boundary
is by btrfs-convert, which will get fixed soon and doesn't get
wide-spread usage.

Signed-off-by: Qu Wenruo <wqu@suse.com>
 fs/btrfs/extent_io.c | 7 +++++++
 1 file changed, 7 insertions(+)
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diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 50cd5efc79ab..28188509a206 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5268,6 +5268,13 @@  struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 		btrfs_err(fs_info, "bad tree block start %llu", start);
 		return ERR_PTR(-EINVAL);
+	if (btrfs_is_subpage(fs_info) && round_down(start, PAGE_SIZE) !=
+	    round_down(start + len - 1, PAGE_SIZE)) {
+		btrfs_err(fs_info,
+		"tree block crosses page boundary, start %llu nodesize %lu",
+			  start, len);
+		return ERR_PTR(-EINVAL);
+	}
 	eb = find_extent_buffer(fs_info, start);
 	if (eb)