[PATCH v2 1/5] fs: fiemap: add physical_length field to extents

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

Some filesystems support compressed extents which have a larger logical
size than physical, and for those filesystems, it can be useful for
userspace to know how much space those extents actually use. For
instance, the compsize [1] tool for btrfs currently uses btrfs-internal,
root-only ioctl to find the actual disk space used by a file; it would
be better and more useful for this information to require fewer
privileges and to be usable on more filesystems. Therefore, use one of
the padding u64s in the fiemap extent structure to return the actual
physical length; and, for now, return this as equal to the logical
length.

[1] https://github.com/kilobyte/compsize

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
 Documentation/filesystems/fiemap.rst | 28 +++++++++++++++++-------
 fs/ioctl.c                           |  3 ++-
 include/uapi/linux/fiemap.h          | 32 ++++++++++++++++++++++------
 3 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/Documentation/filesystems/fiemap.rst b/Documentation/filesystems/fiemap.rst
index 93fc96f760aa..c2bfa107c8d7 100644
--- a/Documentation/filesystems/fiemap.rst
+++ b/Documentation/filesystems/fiemap.rst
@@ -80,14 +80,24 @@ Each extent is described by a single fiemap_extent structure as
 returned in fm_extents::
 
     struct fiemap_extent {
-	    __u64	fe_logical;  /* logical offset in bytes for the start of
-				* the extent */
-	    __u64	fe_physical; /* physical offset in bytes for the start
-				* of the extent */
-	    __u64	fe_length;   /* length in bytes for the extent */
-	    __u64	fe_reserved64[2];
-	    __u32	fe_flags;    /* FIEMAP_EXTENT_* flags for this extent */
-	    __u32	fe_reserved[3];
+            /*
+             * logical offset in bytes for the start of
+             * the extent from the beginning of the file
+             */
+            __u64 fe_logical;
+            /*
+             * physical offset in bytes for the start
+             * of the extent from the beginning of the disk
+             */
+            __u64 fe_physical;
+            /* logical length in bytes for this extent */
+            __u64 fe_logical_length;
+            /* physical length in bytes for this extent */
+            __u64 fe_physical_length;
+            __u64 fe_reserved64[1];
+            /* FIEMAP_EXTENT_* flags for this extent */
+            __u32 fe_flags;
+            __u32 fe_reserved[3];
     };
 
 All offsets and lengths are in bytes and mirror those on disk.  It is valid
@@ -175,6 +185,8 @@ FIEMAP_EXTENT_MERGED
   userspace would be highly inefficient, the kernel will try to merge most
   adjacent blocks into 'extents'.
 
+FIEMAP_EXTENT_HAS_PHYS_LEN
+  This will be set if the file system populated the physical length field.
 
 VFS -> File System Implementation
 ---------------------------------
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 1d5abfdf0f22..850ad46fd923 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -138,7 +138,8 @@ int fiemap_fill_next_extent(struct fiemap_extent_info *fieinfo, u64 logical,
 	memset(&extent, 0, sizeof(extent));
 	extent.fe_logical = logical;
 	extent.fe_physical = phys;
-	extent.fe_length = len;
+	extent.fe_logical_length = len;
+	extent.fe_physical_length = len;
 	extent.fe_flags = flags;
 
 	dest += fieinfo->fi_extents_mapped;
diff --git a/include/uapi/linux/fiemap.h b/include/uapi/linux/fiemap.h
index 24ca0c00cae3..3079159b8e94 100644
--- a/include/uapi/linux/fiemap.h
+++ b/include/uapi/linux/fiemap.h
@@ -14,14 +14,30 @@
 
 #include <linux/types.h>
 
+/*
+ * For backward compatibility, where the member of the struct was called
+ * fe_length instead of fe_logical_length.
+ */
+#define fe_length fe_logical_length
+
 struct fiemap_extent {
-	__u64 fe_logical;  /* logical offset in bytes for the start of
-			    * the extent from the beginning of the file */
-	__u64 fe_physical; /* physical offset in bytes for the start
-			    * of the extent from the beginning of the disk */
-	__u64 fe_length;   /* length in bytes for this extent */
-	__u64 fe_reserved64[2];
-	__u32 fe_flags;    /* FIEMAP_EXTENT_* flags for this extent */
+	/*
+	 * logical offset in bytes for the start of
+	 * the extent from the beginning of the file
+	 */
+	__u64 fe_logical;
+	/*
+	 * physical offset in bytes for the start
+	 * of the extent from the beginning of the disk
+	 */
+	__u64 fe_physical;
+	/* logical length in bytes for this extent */
+	__u64 fe_logical_length;
+	/* physical length in bytes for this extent */
+	__u64 fe_physical_length;
+	__u64 fe_reserved64[1];
+	/* FIEMAP_EXTENT_* flags for this extent */
+	__u32 fe_flags;
 	__u32 fe_reserved[3];
 };
 
@@ -66,5 +82,7 @@ struct fiemap {
 						    * merged for efficiency. */
 #define FIEMAP_EXTENT_SHARED		0x00002000 /* Space shared with other
 						    * files. */
+#define FIEMAP_EXTENT_HAS_PHYS_LEN	0x00004000 /* Physical length is valid
+						    * and set by FS. */
 
 #endif /* _UAPI_LINUX_FIEMAP_H */
-- 
2.43.0