fuse: advertise support for iomap Advertise our new IO paths programmatically by creating an ioctl that can return the capabilities of the kernel. Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 503d877..06e996c 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c

@@ -2643,6 +2643,8 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 
 	case FUSE_DEV_IOC_IOMAP_DEV_ADD:
 		return fuse_dev_ioctl_iomap_dev_add(file, argp);
+	case FUSE_DEV_IOC_IOMAP_SUPPORT:
+		return fuse_dev_ioctl_iomap_support(file, argp);
 
 	default:
 		return -ENOTTY;

diff --git a/fs/fuse/file_iomap.c b/fs/fuse/file_iomap.c
index c41a28a..4511c60 100644
--- a/fs/fuse/file_iomap.c
+++ b/fs/fuse/file_iomap.c

@@ -1644,3 +1644,18 @@ fuse_iomap_fallocate(
 
 	return 0;
 }
+
+int fuse_dev_ioctl_iomap_support(struct file *file,
+				 struct fuse_iomap_support __user *argp)
+{
+	struct fuse_iomap_support ios = { };
+
+	if (fuse_iomap_enabled())
+		ios.flags = FUSE_IOMAP_SUPPORT_BASICS |
+			    FUSE_IOMAP_SUPPORT_DIRECTIO |
+			    FUSE_IOMAP_SUPPORT_PAGECACHE;
+
+	if (copy_to_user(argp, &ios, sizeof(ios)))
+		return -EFAULT;
+	return 0;
+}

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 760043c..a3d4b00 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h

@@ -1701,6 +1701,9 @@ int fuse_iomap_setsize(struct inode *inode, loff_t newsize);
 void fuse_iomap_set_i_blkbits(struct inode *inode, u8 new_blkbits);
 int fuse_iomap_fallocate(struct file *file, int mode, loff_t offset,
 			 loff_t length, loff_t new_size);
+
+int fuse_dev_ioctl_iomap_support(struct file *file,
+				 struct fuse_iomap_support __user *argp);
 #else
 # define fuse_iomap_enabled(...)		(false)
 # define fuse_has_iomap(...)			(false)
@@ -1728,6 +1731,7 @@ int fuse_iomap_fallocate(struct file *file, int mode, loff_t offset,
 # define fuse_iomap_setsize(...)		(-ENOSYS)
 # define fuse_iomap_set_i_blkbits(...)		((void)0)
 # define fuse_iomap_fallocate(...)		(-ENOSYS)
+# define fuse_dev_ioctl_iomap_support(...)	(-EOPNOTSUPP)
 #endif
 
 #endif /* _FS_FUSE_I_H */

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index db3bf4b..fea829c 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h

@@ -1138,6 +1138,17 @@ struct fuse_backing_map {
 	uint64_t	padding;
 };
 
+/* basic reporting functionality */
+#define FUSE_IOMAP_SUPPORT_BASICS	(1ULL << 0)
+/* fuse driver can do direct io */
+#define FUSE_IOMAP_SUPPORT_DIRECTIO	(1ULL << 1)
+/* fuse driver can do buffered io */
+#define FUSE_IOMAP_SUPPORT_PAGECACHE	(1ULL << 2)
+struct fuse_iomap_support {
+	uint64_t	flags;
+	uint64_t	padding;
+};
+
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
 #define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
@@ -1146,6 +1157,8 @@ struct fuse_backing_map {
 #define FUSE_DEV_IOC_BACKING_CLOSE	_IOW(FUSE_DEV_IOC_MAGIC, 2, uint32_t)
 #define FUSE_DEV_IOC_IOMAP_DEV_ADD	_IOW(FUSE_DEV_IOC_MAGIC, 3, \
 					     struct fuse_backing_map)
+#define FUSE_DEV_IOC_IOMAP_SUPPORT	_IOR(FUSE_DEV_IOC_MAGIC, 4, \
+					     struct fuse_iomap_support)
 
 struct fuse_lseek_in {
 	uint64_t	fh;