Patch "btrfs: put initial index value of a directory in a constant" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    btrfs: put initial index value of a directory in a constant

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     btrfs-put-initial-index-value-of-a-directory-in-a-co.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b98bf60ba7f3f2a51fd3ffa649259d93fdf58fc1
Author: Filipe Manana <fdmanana@xxxxxxxx>
Date:   Wed Dec 15 12:19:59 2021 +0000

    btrfs: put initial index value of a directory in a constant
    
    [ Upstream commit 528ee697126fddaff448897c2d649bd756153c79 ]
    
    At btrfs_set_inode_index_count() we refer twice to the number 2 as the
    initial index value for a directory (when it's empty), with a proper
    comment explaining the reason for that value. In the next patch I'll
    have to use that magic value in the directory logging code, so put
    the value in a #define at btrfs_inode.h, to avoid hardcoding the
    magic value again at tree-log.c.
    
    Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
    Signed-off-by: David Sterba <dsterba@xxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 76ee1452c57ba..37ceea85b871c 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -13,6 +13,13 @@
 #include "ordered-data.h"
 #include "delayed-inode.h"
 
+/*
+ * Since we search a directory based on f_pos (struct dir_context::pos) we have
+ * to start at 2 since '.' and '..' have f_pos of 0 and 1 respectively, so
+ * everybody else has to start at 2 (see btrfs_real_readdir() and dir_emit_dots()).
+ */
+#define BTRFS_DIR_START_INDEX 2
+
 /*
  * ordered_data_close is set by truncate when a file that used
  * to have good data has been truncated to zero.  When it is set
@@ -164,8 +171,9 @@ struct btrfs_inode {
 	u64 disk_i_size;
 
 	/*
-	 * if this is a directory then index_cnt is the counter for the index
-	 * number for new files that are created
+	 * If this is a directory then index_cnt is the counter for the index
+	 * number for new files that are created. For an empty directory, this
+	 * must be initialized to BTRFS_DIR_START_INDEX.
 	 */
 	u64 index_cnt;
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ac6ba984973c0..26a4acb856a38 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6396,14 +6396,8 @@ static int btrfs_set_inode_index_count(struct btrfs_inode *inode)
 		goto out;
 	ret = 0;
 
-	/*
-	 * MAGIC NUMBER EXPLANATION:
-	 * since we search a directory based on f_pos we have to start at 2
-	 * since '.' and '..' have f_pos of 0 and 1 respectively, so everybody
-	 * else has to start at 2
-	 */
 	if (path->slots[0] == 0) {
-		inode->index_cnt = 2;
+		inode->index_cnt = BTRFS_DIR_START_INDEX;
 		goto out;
 	}
 
@@ -6414,7 +6408,7 @@ static int btrfs_set_inode_index_count(struct btrfs_inode *inode)
 
 	if (found_key.objectid != btrfs_ino(inode) ||
 	    found_key.type != BTRFS_DIR_INDEX_KEY) {
-		inode->index_cnt = 2;
+		inode->index_cnt = BTRFS_DIR_START_INDEX;
 		goto out;
 	}