[PATCH v2 8/8] fuse: add support for striped backing

[Miklos Szeredi <mszeredi@redhat.com>]

Add the FUSE_BACKING_MAP_CYCLIC flag for FUSE_NOTIFY_BACKING_MAP
notifications to enable creating striped maps.

This is just a set of regular extents that repeats after the end of the
last extent using a striping pattern (i.e. on the target backings the
stripes have a contiguous footprint).

Two additional limits apply compared to non-cyclic extent map population:

 - the size of the extents (chunk size) must be equal

 - the extents must start from zero offset and follow each other without
   gaps.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/fuse/ext_map.c         | 27 ++++++++++++++++++++++++---
 fs/fuse/fuse_i.h          |  1 +
 fs/fuse/notify.c          |  2 +-
 include/uapi/linux/fuse.h |  5 ++++-
 4 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/ext_map.c b/fs/fuse/ext_map.c
index 61cb22e821b6..356a5ec4f5e1 100644
--- a/fs/fuse/ext_map.c
+++ b/fs/fuse/ext_map.c
@@ -101,12 +101,18 @@ static int fuse_ext_map_iomap_begin(struct inode *inode, loff_t offset, loff_t l
 {
 	struct fuse_backing *fb = fuse_inode_backing(get_fuse_inode(inode));
 	struct fuse_iext *fie;
+	u64 ncycle = 0, seq_off = 0, addr, tmp;
 	loff_t ext_len;
 
 	if (!fb || fb->type != FUSE_BACKING_EXTMAP)
 		return fuse_EIO("missing or wrong type backing");
 
-	fie = fuse_find_extent(&fb->extents, offset);
+	if (fb->cycle_length) {
+		ncycle = div64_u64(offset, fb->cycle_length);
+		seq_off = ncycle * fb->cycle_length;
+	}
+
+	fie = fuse_find_extent(&fb->extents, offset - seq_off);
 	if (!fie)
 		return fuse_EIO("missing mapping");
 
@@ -119,9 +125,12 @@ static int fuse_ext_map_iomap_begin(struct inode *inode, loff_t offset, loff_t l
 	}
 
 	ext_len = fie->end - fie->start;
+	addr = fie->backing_offset;
+	if (check_mul_overflow(ncycle, ext_len, &tmp) || check_add_overflow(addr, tmp, &addr))
+		return fuse_EIO("extent address overflow");
 
-	iomap->offset = fie->start;
-	iomap->addr = fie->backing_offset;
+	iomap->offset = fie->start + seq_off;
+	iomap->addr = addr;
 	iomap->length = ext_len;
 	iomap->dax_dev = fie->backing->dax_dev;
 	iomap->type = IOMAP_MAPPED;
@@ -242,6 +251,7 @@ int fuse_ext_map_populate(struct fuse_conn *fc, struct fuse_notify_backing_map_o
 	struct fuse_backing *fb;
 	unsigned int i;
 	int err;
+	u64 chunk_size = 0;
 
 	if (!arg->num_extents)
 		return fuse_EIO("no extents");
@@ -259,7 +269,18 @@ int fuse_ext_map_populate(struct fuse_conn *fc, struct fuse_notify_backing_map_o
 		return -EINVAL;
 	}
 
+	if (arg->flags & FUSE_BACKING_MAP_CYCLIC) {
+		chunk_size = ext[0].length;
+		err = -EINVAL;
+		if (check_mul_overflow(chunk_size, arg->num_extents, &fb->cycle_length))
+			goto err_put;
+	}
+
 	for (i = 0; i < arg->num_extents; i++) {
+		err = -EINVAL;
+		if (chunk_size && (ext[i].offset != chunk_size * i || ext[i].length != chunk_size))
+			goto err_put;
+
 		err = fuse_add_extent(fc, &fb->extents, &ext[i]);
 		if (err)
 			goto err_put;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 7248588b45c4..83cc1dd67cef 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -110,6 +110,7 @@ struct fuse_backing {
 		};
 		struct {
 			struct rb_root extents;
+			u64 cycle_length;
 		};
 	};
 	u64 backing_id;
diff --git a/fs/fuse/notify.c b/fs/fuse/notify.c
index 3bfedd0cdbdd..31172de72477 100644
--- a/fs/fuse/notify.c
+++ b/fs/fuse/notify.c
@@ -461,7 +461,7 @@ static int fuse_notify_map(struct fuse_conn *fc, unsigned int size,
 	if (outarg.reserved[0] != 0 || outarg.reserved[1] != 0)
 		return -EINVAL;
 
-	if (outarg.flags & ~FUSE_BACKING_MAP_CREATE)
+	if (outarg.flags & ~(FUSE_BACKING_MAP_CREATE | FUSE_BACKING_MAP_CYCLIC))
 		return -EINVAL;
 
 	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index b17786492f0b..f371acb73cda 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -255,7 +255,8 @@
  *  - add FUSE_DEV_IOC_BACKING_CREATE, struct fuse_backing_create_in
  *  - add FUSE_NOTIFY_BACKING_REMOVE, struct fuse_notify_backing_remove_out
  *  - add backing_id_64 to fuse_open_out
- *  - add FUSE_NOTIFY_BACKING_MAP, fuse_notify_backing_map_out, fuse_extent, FUSE_BACKING_MAP_CREATE
+ *  - add FUSE_NOTIFY_BACKING_MAP, fuse_notify_backing_map_out, fuse_extent
+ *  - add FUSE_BACKING_MAP_CREATE, FUSE_BACKING_MAP_CYCLIC
  */
 
 #ifndef _LINUX_FUSE_H
@@ -1219,8 +1220,10 @@ struct fuse_notify_backing_remove_out {
  * notify_map flags
  *
  * FUSE_BACKING_MAP_CREATE:	create backing with the supplied ID
+ * FUSE_BACKING_MAP_CYCLIC:	map repeats after last extent
  */
 #define FUSE_BACKING_MAP_CREATE	(1 << 0)
+#define FUSE_BACKING_MAP_CYCLIC	(1 << 1)
 
 struct fuse_notify_backing_map_out {
 	uint64_t	backing_id;
-- 
2.54.0