mm/damon: deprecate DAMON debugfs interface

Changes from v1
(https://lore.kernel.org/damon/[email protected]/)
- Split DAMON debugfs file open warning message (Randy Dunlap)

-----

DAMON debugfs interface has announced to be deprecated after >v5.15 LTS kernel is released. And, v6.1.y has announced to be an LTS[1].

Though the announcement was there for a while, some people might not noticed that so far. Also, some users could depend on it and have problems at movng to the alternative (DAMON sysfs interface).

For such cases, keep the code and documents with warning messages and contacts to ask helps for the deprecation.

[1] https://git.kernel.org/pub/scm/docs/kernel/website.git/commit/?id=332e9121320bc7461b2d3a79665caf153e51732c

SeongJae Park (3):
Docs/admin-guide/mm/damon/usage: add DAMON debugfs interface
deprecation notice
mm/damon/Kconfig: add DAMON debugfs interface deprecation notice mm/damon/dbgfs: print DAMON debugfs interface deprecation message

 Documentation/admin-guide/mm/damon/usage.rst | 20 +++++++++++++-------
 mm/damon/Kconfig                             |  7 ++++---
 mm/damon/dbgfs.c                             | 19 +++++++++++++++++++
 3 files changed, 36 insertions(+), 10 deletions(-)

2.25.1

DAMON debugfs interface has announced to be deprecated after >v5.15 LTS kernel is released. And, v6.1.y has announced to be an LTS[1].

Though the announcement was there for a while, some people might not noticed that so far. Also, some users could depend on it and have problems at movng to the alternative (DAMON sysfs interface).

For such cases, note DAMON debugfs interface as deprecated, and contacts to ask helps on the document.

[1] https://git.kernel.org/pub/scm/docs/kernel/website.git/commit/?id=332e9121320bc7461b2d3a79665caf153e51732c

---
 Documentation/admin-guide/mm/damon/usage.rst | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

index 9237d6a25897..9b823fec974d 100644
@@ -25,10 +25,12 @@ DAMON provides below interfaces for different users.
   interface provides only simple :ref:`statistics <damos_stats>` for the
   monitoring results.  For detailed monitoring results, DAMON provides a
   :ref:`tracepoint <tracepoint>`.
-- *debugfs interface.*
+- *debugfs interface. (DEPRECATED!)*
   :ref:`This <debugfs_interface>` is almost identical to :ref:`sysfs interface
-  <sysfs_interface>`.  This will be removed after next LTS kernel is released,
-  so users should move to the :ref:`sysfs interface <sysfs_interface>`.
+  <sysfs_interface>`.  This is deprecated, so users should move to the
+  :ref:`sysfs interface <sysfs_interface>`.  If you depend on this and cannot
+  move, please report your usecase to [email protected] and
+  [email protected].
 - *Kernel Space Programming Interface.*
   :doc:`This </mm/damon/api>` is for kernel space programmers.  Using this,
   users can utilize every feature of DAMON most flexibly and efficiently by

@@ -487,13 +489,17 @@ the files as above.  Above is only for an example.
 
 .. _debugfs_interface:
 
-debugfs Interface
-=================
+debugfs Interface (DEPRECATED!)
+===============================
 
 .. note::
 
-  DAMON debugfs interface will be removed after next LTS kernel is released, so
-  users should move to the :ref:`sysfs interface <sysfs_interface>`.
+  THIS IS DEPRECATED!
+
+  DAMON debugfs interface is deprecated, so users should move to the
+  :ref:`sysfs interface <sysfs_interface>`.  If you depend on this and cannot
+  move, please report your usecase to [email protected] and
+  [email protected].
 
 DAMON exports eight files, ``attrs``, ``target_ids``, ``init_regions``,
 ``schemes``, ``monitor_on``, ``kdamond_pid``, ``mk_contexts`` and

2.25.1

DAMON debugfs interface has announced to be deprecated after >v5.15 LTS kernel is released. And, v6.1.y has announced to be an LTS[1].

Though the announcement was there for a while, some people might not noticed that so far. Also, some users could depend on it and have problems at movng to the alternative (DAMON sysfs interface).

For such cases, note DAMON debugfs interface as deprecated, and contacts to ask helps on the Kconfig.

[1] https://git.kernel.org/pub/scm/docs/kernel/website.git/commit/?id=332e9121320bc7461b2d3a79665caf153e51732c

---
 mm/damon/Kconfig | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

index 7821fcb3f258..436c6b4cb5ec 100644
@@ -60,7 +60,7 @@ config DAMON_SYSFS
 	  the interface for arbitrary data access monitoring.
 
 config DAMON_DBGFS
-	bool "DAMON debugfs interface"
+	bool "DAMON debugfs interface (DEPRECATED!)"
 	depends on DAMON_VADDR && DAMON_PADDR && DEBUG_FS
 	help
 	  This builds the debugfs interface for DAMON.  The user space admins

@@ -68,8 +68,9 @@ config DAMON_DBGFS
 
 	  If unsure, say N.
 
-	  This will be removed after >5.15.y LTS kernel is released, so users
-	  should move to the sysfs interface (DAMON_SYSFS).
+	  This is deprecated, so users should move to the sysfs interface
+	  (DAMON_SYSFS).  If you depend on this and cannot move, please report
+	  your usecase to [email protected] and [email protected].
 
 config DAMON_DBGFS_KUNIT_TEST
 	bool "Test for damon debugfs interface" if !KUNIT_ALL_TESTS

2.25.1

DAMON debugfs interface has announced to be deprecated after >v5.15 LTS kernel is released. And, v6.1.y has announced to be an LTS[1].

Though the announcement was there for a while, some people might not noticed that so far. Also, some users could depend on it and have problems at movng to the alternative (DAMON sysfs interface).

For such cases, warn DAMON debugfs interface deprecation with contacts to ask helps when any DAMON debugfs interface file is opened.

[1] https://git.kernel.org/pub/scm/docs/kernel/website.git/commit/?id=332e9121320bc7461b2d3a79665caf153e51732c

---
 mm/damon/dbgfs.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

index b3f454a5c682..124f0f8c97b7 100644
@@ -20,6 +20,14 @@ static int dbgfs_nr_ctxs;
 static struct dentry **dbgfs_dirs;
 static DEFINE_MUTEX(damon_dbgfs_lock);
 
+static void damon_dbgfs_warn_deprecation(void)
+{
+	pr_warn_once("DAMON debugfs interface is deprecated, "
+		     "so users should move to DAMON_SYSFS. If you cannot, "
+		     "please report your usecase to [email protected] and "
+		     "[email protected].\n");
+}
+
 /*
  * Returns non-empty string on success, negative error code otherwise.
  */

@@ -711,6 +719,8 @@ static ssize_t dbgfs_kdamond_pid_read(struct file *file,
 
 static int damon_dbgfs_open(struct inode *inode, struct file *file)
 {
+	damon_dbgfs_warn_deprecation();
+
 	file->private_data = inode->i_private;
 
 	return nonseekable_open(inode, file);

@@ -1039,15 +1049,24 @@ static ssize_t dbgfs_monitor_on_write(struct file *file,
 	return ret;
 }
 
+static int damon_dbgfs_static_file_open(struct inode *inode, struct file *file)
+{
+	damon_dbgfs_warn_deprecation();
+	return nonseekable_open(inode, file);
+}
+
 static const struct file_operations mk_contexts_fops = {
+	.open = damon_dbgfs_static_file_open,
 	.write = dbgfs_mk_context_write,
 };
 
 static const struct file_operations rm_contexts_fops = {
+	.open = damon_dbgfs_static_file_open,
 	.write = dbgfs_rm_context_write,
 };
 
 static const struct file_operations monitor_on_fops = {
+	.open = damon_dbgfs_static_file_open,
 	.read = dbgfs_monitor_on_read,
 	.write = dbgfs_monitor_on_write,
 };

2.25.1

I usually sent this kind of update for after-merged-into-mm-unstable tree patches individusally as fixup, but this time I sent whole patchset as a new version, because I was out of my mind.

For someone who may prefer the usual for-fixup individual patch, attaching the version below.

Thanks,
SJ

================================= 8< ==========================================
From: SeongJae Park <[email protected]>
Date: Fri, 10 Feb 2023 04:37:19 +0000
Subject: [PATCH mm-unstable] mm/damon/dbgfs: break too long deprecation
warning message

DAMON debugfs interface deprecation message, which is introduced by commit 234a68e24b12 ("mm/damon/dbgfs: print DAMON debugfs interface deprecation message") of mm-unstable, is too long. Break down into multiple strings for better code readability.

---
 mm/damon/dbgfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

index e551a20b35e3..124f0f8c97b7 100644
@@ -22,7 +22,10 @@ static DEFINE_MUTEX(damon_dbgfs_lock);
 
 static void damon_dbgfs_warn_deprecation(void)
 {
-       pr_warn_once("DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).  If you depend on this and cannot move, please report your usecase to [email protected] and [email protected].\n");
+       pr_warn_once("DAMON debugfs interface is deprecated, "
+                    "so users should move to DAMON_SYSFS. If you cannot, "
+                    "please report your usecase to [email protected] and "
+                    "[email protected].\n");
 }
 
 /*

--
2.25.1