btrfs: remove unused btrfs_folio_start_writer_lock()

This function is not really suitable to lock a folio, as it lacks the
proper mapping checks, thus the locked folio may not even belong to
btrfs.

And due to the above reason, the last user inside lock_delalloc_folios()
is already removed, and we can remove this function.

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

2 files changed, 0 insertions, 49 deletions

diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 17bc53a8df01..26d4d05dd165 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -295,26 +295,6 @@ static void btrfs_subpage_clamp_range(struct folio *folio, u64 *start, u32 *len)
 			     orig_start + orig_len) - *start;
 }
 
-static void btrfs_subpage_start_writer(const struct btrfs_fs_info *fs_info,
-				       struct folio *folio, u64 start, u32 len)
-{
-	struct btrfs_subpage *subpage = folio_get_private(folio);
-	const int start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
-	const int nbits = (len >> fs_info->sectorsize_bits);
-	unsigned long flags;
-	int ret;
-
-	btrfs_subpage_assert(fs_info, folio, start, len);
-
-	spin_lock_irqsave(&subpage->lock, flags);
-	ASSERT(atomic_read(&subpage->readers) == 0);
-	ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
-	bitmap_set(subpage->bitmaps, start_bit, nbits);
-	ret = atomic_add_return(nbits, &subpage->writers);
-	ASSERT(ret == nbits);
-	spin_unlock_irqrestore(&subpage->lock, flags);
-}
-
 static bool btrfs_subpage_end_and_test_writer(const struct btrfs_fs_info *fs_info,
 					      struct folio *folio, u64 start, u32 len)
 {
@@ -352,33 +332,6 @@ static bool btrfs_subpage_end_and_test_writer(const struct btrfs_fs_info *fs_inf
 }
 
 /*
- * Lock a folio for delalloc page writeback.
- *
- * Return -EAGAIN if the page is not properly initialized.
- * Return 0 with the page locked, and writer counter updated.
- *
- * Even with 0 returned, the page still need extra check to make sure
- * it's really the correct page, as the caller is using
- * filemap_get_folios_contig(), which can race with page invalidating.
- */
-int btrfs_folio_start_writer_lock(const struct btrfs_fs_info *fs_info,
-				  struct folio *folio, u64 start, u32 len)
-{
-	if (unlikely(!fs_info) || !btrfs_is_subpage(fs_info, folio->mapping)) {
-		folio_lock(folio);
-		return 0;
-	}
-	folio_lock(folio);
-	if (!folio_test_private(folio) || !folio_get_private(folio)) {
-		folio_unlock(folio);
-		return -EAGAIN;
-	}
-	btrfs_subpage_clamp_range(folio, &start, &len);
-	btrfs_subpage_start_writer(fs_info, folio, start, len);
-	return 0;
-}
-
-/*
  * Handle different locked folios:
  *
  * - Non-subpage folio
diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index d16fbddeda68..e4076c5b06bc 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -100,8 +100,6 @@ void btrfs_subpage_start_reader(const struct btrfs_fs_info *fs_info,
 void btrfs_subpage_end_reader(const struct btrfs_fs_info *fs_info,
 			      struct folio *folio, u64 start, u32 len);
 
-int btrfs_folio_start_writer_lock(const struct btrfs_fs_info *fs_info,
-				  struct folio *folio, u64 start, u32 len);
 void btrfs_folio_end_writer_lock(const struct btrfs_fs_info *fs_info,
 				 struct folio *folio, u64 start, u32 len);
 void btrfs_folio_set_writer_lock(const struct btrfs_fs_info *fs_info,