linux-kernel - [PATCH V3 12/21] famfs_fuse: Basic fuse kernel ABI enablement for famfs

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Message-ID: <20260107153332.64727-13-john@groves.net>
Date: Wed,  7 Jan 2026 09:33:21 -0600
From: John Groves <John@...ves.net>
To: John Groves <John@...ves.net>,
	Miklos Szeredi <miklos@...redi.hu>,
	Dan Williams <dan.j.williams@...el.com>,
	Bernd Schubert <bschubert@....com>,
	Alison Schofield <alison.schofield@...el.com>
Cc: John Groves <jgroves@...ron.com>,
	Jonathan Corbet <corbet@....net>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	David Hildenbrand <david@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	"Darrick J . Wong" <djwong@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Jeff Layton <jlayton@...nel.org>,
	Amir Goldstein <amir73il@...il.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
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	Joanne Koong <joannelkoong@...il.com>,
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	Bagas Sanjaya <bagasdotme@...il.com>,
	Chen Linxuan <chenlinxuan@...ontech.com>,
	James Morse <james.morse@....com>,
	Fuad Tabba <tabba@...gle.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Shivank Garg <shivankg@....com>,
	Ackerley Tng <ackerleytng@...gle.com>,
	Gregory Price <gourry@...rry.net>,
	Aravind Ramesh <arramesh@...ron.com>,
	Ajay Joshi <ajayjoshi@...ron.com>,
	venkataravis@...ron.com,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	linux-cxl@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	John Groves <john@...ves.net>
Subject: [PATCH V3 12/21] famfs_fuse: Basic fuse kernel ABI enablement for famfs

* FUSE_DAX_FMAP flag in INIT request/reply

* fuse_conn->famfs_iomap (enable famfs-mapped files) to denote a
  famfs-enabled connection

Signed-off-by: John Groves <john@...ves.net>
---
 fs/fuse/fuse_i.h          | 3 +++
 fs/fuse/inode.c           | 6 ++++++
 include/uapi/linux/fuse.h | 5 +++++
 3 files changed, 14 insertions(+)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 17736c0a6d2f..ec2446099010 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -921,6 +921,9 @@ struct fuse_conn {
 	/* Is synchronous FUSE_INIT allowed? */
 	unsigned int sync_init:1;
 
+	/* dev_dax_iomap support for famfs */
+	unsigned int famfs_iomap:1;
+
 	/* Use io_uring for communication */
 	unsigned int io_uring;
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index ed667920997f..acabf92a11f8 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1456,6 +1456,10 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 
 			if (flags & FUSE_REQUEST_TIMEOUT)
 				timeout = arg->request_timeout;
+
+			if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) &&
+			    flags & FUSE_DAX_FMAP)
+				fc->famfs_iomap = 1;
 		} else {
 			ra_pages = fc->max_read / PAGE_SIZE;
 			fc->no_lock = 1;
@@ -1517,6 +1521,8 @@ static struct fuse_init_args *fuse_new_init(struct fuse_mount *fm)
 		flags |= FUSE_SUBMOUNTS;
 	if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
 		flags |= FUSE_PASSTHROUGH;
+	if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
+		flags |= FUSE_DAX_FMAP;
 
 	/*
 	 * This is just an information flag for fuse server. No need to check
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index c13e1f9a2f12..5e2c93433823 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -240,6 +240,9 @@
  *  - add FUSE_COPY_FILE_RANGE_64
  *  - add struct fuse_copy_file_range_out
  *  - add FUSE_NOTIFY_PRUNE
+ *
+ *  7.46
+ *    - Add FUSE_DAX_FMAP capability - ability to handle in-kernel fsdax maps
  */
 
 #ifndef _LINUX_FUSE_H
@@ -448,6 +451,7 @@ struct fuse_file_lock {
  * FUSE_OVER_IO_URING: Indicate that client supports io-uring
  * FUSE_REQUEST_TIMEOUT: kernel supports timing out requests.
  *			 init_out.request_timeout contains the timeout (in secs)
+ * FUSE_DAX_FMAP: kernel supports dev_dax_iomap (aka famfs) fmaps
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -495,6 +499,7 @@ struct fuse_file_lock {
 #define FUSE_ALLOW_IDMAP	(1ULL << 40)
 #define FUSE_OVER_IO_URING	(1ULL << 41)
 #define FUSE_REQUEST_TIMEOUT	(1ULL << 42)
+#define FUSE_DAX_FMAP		(1ULL << 43)
 
 /**
  * CUSE INIT request/reply flags
-- 
2.49.0