linux-kernel - [PATCH v2 09/16] doc: update porting, vfs documentation for mmap

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Message-ID: <e50e91a6f6173f81addb838c5049bed2833f7b0d.1757534913.git.lorenzo.stoakes@oracle.com>
Date: Wed, 10 Sep 2025 21:22:04 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, Matthew Wilcox <willy@...radead.org>,
        Guo Ren <guoren@...nel.org>,
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Subject: [PATCH v2 09/16] doc: update porting, vfs documentation for mmap_prepare actions

Now we have introduced the ability to specify that actions should be taken
after a VMA is established via the vm_area_desc->action field as specified
in mmap_prepare, update both the VFS documentation and the porting guide to
describe this.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 Documentation/filesystems/porting.rst | 5 +++++
 Documentation/filesystems/vfs.rst     | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 85f590254f07..6743ed0b9112 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -1285,3 +1285,8 @@ rather than a VMA, as the VMA at this stage is not yet valid.
 The vm_area_desc provides the minimum required information for a filesystem
 to initialise state upon memory mapping of a file-backed region, and output
 parameters for the file system to set this state.
+
+In nearly all cases, this is all that is required for a filesystem. However, if
+a filesystem needs to perform an operation such a pre-population of page tables,
+then that action can be specified in the vm_area_desc->action field, which can
+be configured using the mmap_action_*() helpers.
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 486a91633474..9e96c46ee10e 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -1236,6 +1236,10 @@ otherwise noted.
 	file-backed memory mapping, most notably establishing relevant
 	private state and VMA callbacks.
 
+	If further action such as pre-population of page tables is required,
+	this can be specified by the vm_area_desc->action field and related
+	parameters.
+
 Note that the file operations are implemented by the specific
 filesystem in which the inode resides.  When opening a device node
 (character or block special) most filesystems will call special
-- 
2.51.0