[PATCH V4 11/19] famfs_fuse: Basic fuse kernel ABI enablement for famfs

[John Groves <John@Groves.net>]

This patch starts the kernel ABI enablement of famfs in fuse.

- Kconfig: Add FUSE_FAMFS_DAX config parameter, to control
  compilation of famfs within fuse.
- FUSE_DAX_FMAP flag in INIT request/reply
- fuse_conn->famfs_iomap (enable famfs-mapped files) to denote a
  famfs-enabled connection

Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: John Groves <john@groves.net>
---
 fs/fuse/Kconfig           | 14 ++++++++++++++
 fs/fuse/fuse_i.h          |  3 +++
 fs/fuse/inode.c           |  6 ++++++
 include/uapi/linux/fuse.h |  5 +++++
 4 files changed, 28 insertions(+)

diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig
index 3a4ae632c94a..5ca9fae62c7b 100644
--- a/fs/fuse/Kconfig
+++ b/fs/fuse/Kconfig
@@ -76,3 +76,17 @@ config FUSE_IO_URING
 
 	  If you want to allow fuse server/client communication through io-uring,
 	  answer Y
+
+config FUSE_FAMFS_DAX
+	bool "FUSE support for fs-dax filesystems backed by devdax"
+	depends on FUSE_FS
+	depends on DEV_DAX
+	depends on FS_DAX
+	default FUSE_FS
+	help
+	  This enables the fabric-attached memory file system (famfs),
+	  which enables formatting devdax memory as a file system. Famfs
+	  is primarily intended for scale-out shared access to
+	  disaggregated memory.
+
+	  To enable famfs or other fuse/fs-dax file systems, answer Y
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 45e108dec771..2839efb219a9 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..25686f088e6a 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
-- 
2.52.0