linux-ext4 - [Bug 196405] mkdir mishandles st_nlink in ext4 directory with 64997 subdirectories

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Message-ID: <bug-196405-13602-0nvcojS9I8@https.bugzilla.kernel.org/>
Date:   Sun, 23 Jul 2017 22:55:14 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...nel.org
Subject: [Bug 196405] mkdir mishandles st_nlink in ext4 directory with 64997
 subdirectories

https://bugzilla.kernel.org/show_bug.cgi?id=196405

--- Comment #24 from Theodore Tso (tytso@....edu) ---
An update to e2fsprogs to clarify how dir_nlink works in the ext4 man
page.

                                - Ted

commit 7d8f358cdce948df57b1001b9c278f33519afa86
Author: Theodore Ts'o <tytso@....edu>
Date:   Sun Jul 23 18:51:22 2017 -0400

    Clarify how the description of the dir_nlink feature in the ext4 man page

    Signed-off-by: Theodore Ts'o <tytso@....edu>

diff --git a/misc/ext4.5.in b/misc/ext4.5.in
index c1e67abbc..3511dae62 100644
--- a/misc/ext4.5.in
+++ b/misc/ext4.5.in
@@ -69,7 +69,12 @@ ext2 file systems.
 .TP
 .B dir_nlink
 .br
-This ext4 feature allows more than 65000 subdirectories per directory.
+Normally ext4 allows an inode to have no more than 65,000 hard links.
+This applies to files as well as directories, which means that there can
+be no more than 64,998 subdirectories in a directory (because each of
+the '..' entries counts as a hard link).  This feature lifts this limit
+by causing ext4 to use a links count of 1 to indicate that the number of
+hard links to a directory is not known.
 .TP
 .B encrypt
 .br

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