[RFC v1] man/man3/readdir.3, man/man3type/stat.3type: Improve documentation about .d_ino and .st_ino

[Alejandro Colomar <alx@kernel.org>]

Suggested-by: Pali Rohár <pali@kernel.org>
Co-authored-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---
 man/man3/readdir.3      | 22 +++++++++++++++++++++-
 man/man3type/stat.3type | 16 +++++++++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/man/man3/readdir.3 b/man/man3/readdir.3
index b9150160b..ad9c76595 100644
--- a/man/man3/readdir.3
+++ b/man/man3/readdir.3
@@ -58,7 +58,27 @@ .SH DESCRIPTION
 structure are as follows:
 .TP
 .I .d_ino
-This is the inode number of the file.
+This is the inode number of the file,
+which belongs to the filesystem
+.I .st_dev
+(see
+.BR stat (3type))
+of the directory on which
+.BR readdir ()
+was called.
+If the directory entry is the mount point,
+then
+.I .d_ino
+differs from
+.IR .st_ino :
+.I .d_ino
+is the inode number of the underlying mount point,
+while
+.I .st_ino
+is the inode number of the mounted file system.
+According to POSIX,
+this Linux behavior is considered to be a bug,
+but is nevertheless conforming.
 .TP
 .I .d_off
 The value returned in
diff --git a/man/man3type/stat.3type b/man/man3type/stat.3type
index ee801bcec..835626775 100644
--- a/man/man3type/stat.3type
+++ b/man/man3type/stat.3type
@@ -66,7 +66,21 @@ .SH DESCRIPTION
 macros may be useful to decompose the device ID in this field.)
 .TP
 .I .st_ino
-This field contains the file's inode number.
+This field contains the file's inode number,
+which belongs to the
+.IR .st_dev .
+If
+.BR stat (2)
+was called on the mount point,
+then
+.I .d_ino
+differs from
+.IR .st_ino :
+.I .d_ino
+is the inode number of the underlying mount point,
+while
+.I .st_ino
+is the inode number of the mounted file system.
 .TP
 .I .st_mode
 This field contains the file type and mode.

Range-diff against v0:
-:  --------- > 1:  c27a2d7f8 man/man3/readdir.3, man/man3type/stat.3type: Improve documentation about .d_ino and .st_ino
-- 
2.49.0