[PATCH v14 6/6] Documentation: path-lookup: mention LOOKUP_MAGICLINK_JUMPED

Aleksa Sarai
2019-10-10T05:41:40Z

Now that we have a special flag to signify magic-link jumps, mention it
within the path-lookup docs. And now that "magic link" is the correct
term for nd_jump_link()-style symlinks, clean up references to this type
of "symlink".

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
Documentation/filesystems/path-lookup.rst | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst
index 434a07b0002b..2c32795389bd 100644
--- a/Documentation/filesystems/path-lookup.rst
+++ b/Documentation/filesystems/path-lookup.rst
@@ -405,6 +405,10 @@ is requested. Keeping a reference in the ``nameidata`` ensures that
only one root is in effect for the entire path walk, even if it races
with a ``chroot()`` system call.

+It should be noted that in the case of ``LOOKUP_IN_ROOT`` or
+``LOOKUP_BENEATH``, the effective root becomes the directory file descriptor
+passed to ``openat2()`` (which exposes these ``LOOKUP_`` flags).
+
The root is needed when either of two conditions holds: (1) either the
pathname or a symbolic link starts with a "'/'", or (2) a "``..``"
component is being handled, since "``..``" from the root must always stay
@@ -1149,7 +1153,7 @@ so ``NULL`` is returned to indicate that the symlink can be released and
the stack frame discarded.

The other case involves things in ``/proc`` that look like symlinks but
-aren't really::
+aren't really (and are therefore commonly referred to as "magic-links")::

$ ls -l /proc/self/fd/1
lrwx------ 1 neilb neilb 64 Jun 13 10:19 /proc/self/fd/1 -> /dev/pts/4
@@ -1310,12 +1314,14 @@ longer needed.
``LOOKUP_JUMPED`` means that the current dentry was chosen not because
it had the right name but for some other reason. This happens when
following "``..``", following a symlink to ``/``, crossing a mount point
-or accessing a "``/proc/$PID/fd/$FD``" symlink. In this case the
-filesystem has not been asked to revalidate the name (with
-``d_revalidate()``). In such cases the inode may still need to be
-revalidated, so ``d_op->d_weak_revalidate()`` is called if
+or accessing a "``/proc/$PID/fd/$FD``" symlink (also known as a "magic
+link"). In this case the filesystem has not been asked to revalidate the
+name (with ``d_revalidate()``). In such cases the inode may still need
+to be revalidated, so ``d_op->d_weak_revalidate()`` is called if
``LOOKUP_JUMPED`` is set when the look completes - which may be at the
-final component or, when creating, unlinking, or renaming, at the penultimate component.
+final component or, when creating, unlinking, or renaming, at the
+penultimate component. ``LOOKUP_MAGICLINK_JUMPED`` is set alongside
+``LOOKUP_JUMPED`` if a magic-link was traversed.

Final-component flags
~~~~~~~~~~~~~~~~~~~~~
--
2.23.0