[PATCH 11/11] fuse: advertise support for iomap

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Darrick J. Wong <djwong@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 fs/fuse/fuse_i.h          |    4 ++++
 include/uapi/linux/fuse.h |   13 +++++++++++++
 fs/fuse/dev.c             |    3 +++
 fs/fuse/file_iomap.c      |   18 ++++++++++++++++++
 4 files changed, 38 insertions(+)


diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 8481b1d0299df0..5b14e8b23f305f 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1683,6 +1683,9 @@ int fuse_iomap_setsize(struct mnt_idmap *idmap, struct dentry *dentry,
 		       struct iattr *iattr);
 int fuse_iomap_fallocate(struct file *file, int mode, loff_t offset,
 			 loff_t length, loff_t new_size);
+
+int fuse_iomap_ioc_support(struct file *file,
+			   struct fuse_iomap_support __user *argp);
 #else
 # define fuse_iomap_enabled(...)		(false)
 # define fuse_has_iomap(...)			(false)
@@ -1706,6 +1709,7 @@ int fuse_iomap_fallocate(struct file *file, int mode, loff_t offset,
 # define fuse_iomap_buffered_write(...)		(-ENOSYS)
 # define fuse_iomap_setsize(...)		(-ENOSYS)
 # define fuse_iomap_fallocate(...)		(-ENOSYS)
+# define fuse_iomap_ioc_support(...)		(-ENOTTY)
 #endif
 
 #endif /* _FS_FUSE_I_H */
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index c9402f2b2a335c..cbef70ae05c73b 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -1135,12 +1135,25 @@ 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)
 #define FUSE_DEV_IOC_BACKING_OPEN	_IOW(FUSE_DEV_IOC_MAGIC, 1, \
 					     struct fuse_backing_map)
 #define FUSE_DEV_IOC_BACKING_CLOSE	_IOW(FUSE_DEV_IOC_MAGIC, 2, uint32_t)
+#define FUSE_DEV_IOC_IOMAP_SUPPORT	_IOR(FUSE_DEV_IOC_MAGIC, 3, \
+					     struct fuse_iomap_support)
 
 struct fuse_lseek_in {
 	uint64_t	fh;
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 9d7064ec170cf6..91beafbbcf7c02 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2620,6 +2620,9 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 	case FUSE_DEV_IOC_BACKING_CLOSE:
 		return fuse_dev_ioctl_backing_close(file, argp);
 
+	case FUSE_DEV_IOC_IOMAP_SUPPORT:
+		return fuse_iomap_ioc_support(file, argp);
+
 	default:
 		return -ENOTTY;
 	}
diff --git a/fs/fuse/file_iomap.c b/fs/fuse/file_iomap.c
index 746d9ae192dc55..60e1242b32fd7c 100644
--- a/fs/fuse/file_iomap.c
+++ b/fs/fuse/file_iomap.c
@@ -1425,3 +1425,21 @@ fuse_iomap_fallocate(
 
 	return 0;
 }
+
+int fuse_iomap_ioc_support(struct file *file,
+			   struct fuse_iomap_support __user *argp)
+{
+	struct fuse_iomap_support ios = { };
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	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;
+}