[PATCH 2/7] bcachefs: Stash a pointer to the filesystem for blk_holder_ops

[Kent Overstreet <kent.overstreet@linux.dev>]

Note that we open block devices before we allocate bch_fs, but once
attached to a filesystem they will be closed before the bch_fs is torn
down - so stashing a pointer without a refcount looks incorrect but it's
not.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 fs/bcachefs/super-io.c    | 2 +-
 fs/bcachefs/super.c       | 7 +++++++
 fs/bcachefs/super_types.h | 8 +++++++-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index 28724aee2c09..bd24b4f7eeb6 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -748,7 +748,7 @@ static int __bch2_read_super(const char *path, struct bch_opts *opts,
 	memset(sb, 0, sizeof(*sb));
 	sb->mode	= BLK_OPEN_READ;
 	sb->have_bio	= true;
-	sb->holder	= kmalloc(1, GFP_KERNEL);
+	sb->holder	= kzalloc(sizeof(*sb->holder), GFP_KERNEL);
 	if (!sb->holder)
 		return -ENOMEM;
 
diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index 10c281ad96eb..b653dd480591 100644
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -1431,6 +1431,13 @@ static int __bch2_dev_attach_bdev(struct bch_dev *ca, struct bch_sb_handle *sb)
 	ca->disk_sb = *sb;
 	memset(sb, 0, sizeof(*sb));
 
+	/*
+	 * Stash pointer to the filesystem for blk_holder_ops - note that once
+	 * attached to a filesystem, we will always close the block device
+	 * before tearing down the filesystem object.
+	 */
+	ca->disk_sb.holder->c = ca->fs;
+
 	ca->dev = ca->disk_sb.bdev->bd_dev;
 
 	percpu_ref_reinit(&ca->io_ref);
diff --git a/fs/bcachefs/super_types.h b/fs/bcachefs/super_types.h
index 368a63d938cf..3a899f799d1d 100644
--- a/fs/bcachefs/super_types.h
+++ b/fs/bcachefs/super_types.h
@@ -2,13 +2,19 @@
 #ifndef _BCACHEFS_SUPER_TYPES_H
 #define _BCACHEFS_SUPER_TYPES_H
 
+struct bch_fs;
+
+struct bch_sb_handle_holder {
+	struct bch_fs		*c;
+};
+
 struct bch_sb_handle {
 	struct bch_sb		*sb;
 	struct file		*s_bdev_file;
 	struct block_device	*bdev;
 	char			*sb_name;
 	struct bio		*bio;
-	void			*holder;
+	struct bch_sb_handle_holder *holder;
 	size_t			buffer_size;
 	blk_mode_t		mode;
 	unsigned		have_layout:1;
-- 
2.47.2