fs: add i_state helpers

The i_state member is an unsigned long so that it can be used with the
wait bit infrastructure which expects unsigned long. This wastes 4 bytes
which we're unlikely to ever use. Switch to using the var event wait
mechanism using the address of the bit. Thanks to Linus for the address
idea.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index cda1f2545ea0..d35de348d2ec 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -744,6 +744,21 @@ struct inode {
 	void			*i_private; /* fs or device private pointer */
 } __randomize_layout;
 
+/*
+ * Get bit address from inode->i_state to use with wait_var_event()
+ * infrastructre.
+ */
+#define inode_state_wait_address(inode, bit) ((char *)&(inode)->i_state + (bit))
+
+struct wait_queue_head *inode_bit_waitqueue(struct wait_bit_queue_entry *wqe,
+					    struct inode *inode, u32 bit);
+
+static inline void inode_wake_up_bit(struct inode *inode, u32 bit)
+{
+	/* Caller is responsible for correct memory barriers. */
+	wake_up_var(inode_state_wait_address(inode, bit));
+}
+
 struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode);
 
 static inline unsigned int i_blocksize(const struct inode *node)