From e04ef476fd330485e5a88c7018d29c55cf411fe2 Mon Sep 17 00:00:00 2001
From: Richard W.M. Jones <rjones@redhat.com>
Date: Tue, 5 Oct 2010 09:54:10 +0100
Subject: [PATCH] Trace reads and writes to qemu block devices.

NB: This patch is not suitable for nor intended to go upstream in
its current form.

When qemu opens a block device, this patch creates a trace file
in /tmp with a name related to the block device.  Reads and writes
to the device cause lines to be written to the trace file:

  S <total_sectors>
  W <sector> <nb_sectors>
  R <sector> <nb_sectors>

'S' is the summary line, printed first which just tells you how
many sectors are on the device.

'W' and 'R' are writes and reads, for the range <sector> through
to <sector> + <nb_sectors> - 1.
---
 block.c     |   29 +++++++++++++++++++++++++++++
 block_int.h |    3 +++
 2 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index ebbc376..26ead5b 100644
--- a/block.c
+++ b/block.c
@@ -474,6 +474,23 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
         goto free_and_fail;
     }
 
+    /* Open trace file in /tmp based on filename. XXX */
+    size_t len = strlen (filename);
+    char *trace_file = qemu_malloc (10 + len);
+    snprintf (trace_file, 10 + len, "/tmp/%s.qtr", filename);
+    size_t i;
+    for (i = 5; i < 5 + len; ++i) {
+        if (trace_file[i] == '/')
+            trace_file[i] = '_';
+    }
+    bs->trace_fp = fopen (trace_file, "w");
+    if (bs->trace_fp) {
+        setlinebuf (bs->trace_fp);
+        fprintf (bs->trace_fp, "S %" PRIi64 "\n", bs->total_sectors);
+    } else {
+        perror (trace_file);
+    }
+
 #ifndef _WIN32
     if (bs->is_temporary) {
         unlink(filename);
@@ -665,6 +682,10 @@ void bdrv_close(BlockDriverState *bs)
             bdrv_close(bs->file);
         }
 
+        if (bs->trace_fp)
+            fclose (bs->trace_fp);
+        bs->trace_fp = NULL;
+
         /* call the change callback */
         bs->media_changed = 1;
         if (bs->change_cb)
@@ -1995,6 +2016,10 @@ BlockDriverAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
 	/* Update stats even though technically transfer has not happened. */
 	bs->rd_bytes += (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
 	bs->rd_ops ++;
+
+        if (bs->trace_fp)
+            fprintf (bs->trace_fp,
+                     "R %" PRIi64 " %d\n", sector_num, nb_sectors);
     }
 
     return ret;
@@ -2028,6 +2053,10 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
         if (bs->wr_highest_sector < sector_num + nb_sectors - 1) {
             bs->wr_highest_sector = sector_num + nb_sectors - 1;
         }
+
+        if (bs->trace_fp)
+            fprintf (bs->trace_fp,
+                     "W %" PRIi64 " %d\n", sector_num, nb_sectors);
     }
 
     return ret;
diff --git a/block_int.h b/block_int.h
index e8e7156..03e7c9b 100644
--- a/block_int.h
+++ b/block_int.h
@@ -178,6 +178,9 @@ struct BlockDriverState {
     uint64_t wr_ops;
     uint64_t wr_highest_sector;
 
+    /* Trace to file. */
+    FILE *trace_fp;
+
     /* Whether the disk can expand beyond total_sectors */
     int growable;
 
-- 
1.7.3.1