xfs: start documenting common units and tags used in tracepoints

Because there are a lot of tracepoints that express numeric data with an associated unit and tag, document what they are to help everyone else keep these thigns straight. Signed-off-by: Darrick J. Wong <[email protected]> Reviewed-by: Dave Chinner <[email protected]> Reviewed-by: Carlos Maiolino <[email protected]>
torvalds · Aug 19, 2021 · e5f2e54 · e5f2e54
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diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
@@ -2,6 +2,10 @@
 /*
  * Copyright (C) 2017 Oracle. All Rights Reserved.
  * Author: Darrick J. Wong <[email protected]>
+ *
+ * NOTE: none of these tracepoints shall be considered a stable kernel ABI
+ * as they can change at any time. See xfs_trace.h for documentation of
+ * specific units found in tracepoint output.
  */
 #undef TRACE_SYSTEM
 #define TRACE_SYSTEM xfs_scrub

diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
@@ -2,6 +2,41 @@
 /*
  * Copyright (c) 2009, Christoph Hellwig
  * All Rights Reserved.
+ *
+ * NOTE: none of these tracepoints shall be considered a stable kernel ABI
+ * as they can change at any time.
+ *
+ * Current conventions for printing numbers measuring specific units:
+ *
+ * agno: allocation group number
+ *
+ * agino: per-AG inode number
+ * ino: filesystem inode number
+ *
+ * agbno: per-AG block number in fs blocks
+ * startblock: physical block number for file mappings. This is either a
+ * segmented fsblock for data device mappings, or a rfsblock
+ * for realtime device mappings
+ * fsbcount: number of blocks in an extent, in fs blocks
+ *
+ * daddr: physical block number in 512b blocks
+ * bbcount: number of blocks in a physical extent, in 512b blocks
+ *
+ * owner: reverse-mapping owner, usually inodes
+ *
+ * fileoff: file offset, in fs blocks
+ * pos: file offset, in bytes
+ * bytecount: number of bytes
+ *
+ * disize: ondisk file size, in bytes
+ * isize: incore file size, in bytes
+ *
+ * forkoff: inode fork offset, in bytes
+ *
+ * ireccount: number of inode records
+ *
+ * Numbers describing space allocations (blocks, extents, inodes) should be
+ * formatted in hexadecimal.
  */
 #undef TRACE_SYSTEM
 #define TRACE_SYSTEM xfs