[PATCH 1/3] fs: add physical_length field to fiemap 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 | 26 ++++++++++++++++++--------
 fs/ioctl.c                           |  1 +
 include/uapi/linux/fiemap.h          | 24 +++++++++++++++++-------
 3 files changed, 36 insertions(+), 15 deletions(-)

diff --git a/Documentation/filesystems/fiemap.rst b/Documentation/filesystems/fiemap.rst
index 93fc96f760aa..e3e84573b087 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;
+            /* length in bytes for this extent */
+            __u64 fe_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
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 1d5abfdf0f22..f8e5d6dfc62d 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -139,6 +139,7 @@ int fiemap_fill_next_extent(struct fiemap_extent_info *fieinfo, u64 logical,
 	extent.fe_logical = logical;
 	extent.fe_physical = phys;
 	extent.fe_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..fd3c7d380666 100644
--- a/include/uapi/linux/fiemap.h
+++ b/include/uapi/linux/fiemap.h
@@ -15,13 +15,23 @@
 #include <linux/types.h>
 
 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;
+	/* length in bytes for this extent */
+	__u64 fe_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];
 };
 
-- 
2.44.0