[PATCH 4/4 v3] Documentation/fiemap: Document the DATA_COMPRESSED flag

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CC: linux-doc@xxxxxxxxxxxxxxx
CC: Rob Landley <rob@xxxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxx>
---
 Documentation/filesystems/fiemap.txt |   17 +++++++++++++----
 1 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/Documentation/filesystems/fiemap.txt b/Documentation/filesystems/fiemap.txt
index 1b805a0..46bfc1c 100644
--- a/Documentation/filesystems/fiemap.txt
+++ b/Documentation/filesystems/fiemap.txt
@@ -80,10 +80,12 @@ 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_physical; /* physical offset in bytes for the start
+			      * of the extent from the beginning of the disk */
 	__u64	fe_length;   /* length in bytes for the extent */
-	__u64	fe_reserved64[2];
+	__u64   fe_phys_length; /* physical length in bytes, undefined if
+			         * DATA_COMPRESSED not set */
+	__u64	fe_reserved64;
 	__u32	fe_flags;    /* FIEMAP_EXTENT_* flags for this extent */
 	__u32	fe_reserved[3];
 };
@@ -93,7 +95,8 @@ for an extents logical offset to start before the request or its logical
 length to extend past the request.  Unless FIEMAP_EXTENT_NOT_ALIGNED is
 returned, fe_logical, fe_physical, and fe_length will be aligned to the
 block size of the file system.  With the exception of extents flagged as
-FIEMAP_EXTENT_MERGED, adjacent extents will not be merged.
+FIEMAP_EXTENT_MERGED, adjacent extents will not be merged.  The value of
+fe_phys_length is valid only if FIEMAP_EXTENT_DATA_COMPRESSED is set.
 
 The fe_flags field contains flags which describe the extent returned.
 A special flag, FIEMAP_EXTENT_LAST is always set on the last extent in
@@ -143,6 +146,12 @@ unmounted, and then only if the FIEMAP_EXTENT_ENCODED flag is
 clear; user applications must not try reading or writing to the
 filesystem via the block device under any other circumstances.
 
+* FIEMAP_EXTENT_DATA_COMPRESSED
+  - This will also set FIEMAP_EXTENT_ENCODED
+The data in this extent has been compressed by the file system. When
+set, fe_phys_length contains the physical extent length in bytes. The
+value may be rounded depending on the filesystem implementation.
+
 * FIEMAP_EXTENT_DATA_ENCRYPTED
   - This will also set FIEMAP_EXTENT_ENCODED
 The data in this extent has been encrypted by the file system.
-- 
1.7.9

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