qemu-img bench: Make start offset configurable

This patch adds an option the specify the offset of the first request
made by qemu-img bench. This allows to benchmark misaligned requests.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NDenis V. Lunev <den@openvz.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

qemu-img-cmds.hx

@@ -10,9 +10,9 @@ STEXI
 ETEXI
 
 DEF("bench", img_bench,
-    "bench [-c count] [-d depth] [-f fmt] [-n] [--pattern=pattern] [-q] [-s buffer_size] [-t cache] [-w] filename")
+    "bench [-c count] [-d depth] [-f fmt] [-n] [-o offset] [--pattern=pattern] [-q] [-s buffer_size] [-t cache] [-w] filename")
 STEXI
-@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [-n] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-t @var{cache}] [-w] @var{filename}
+@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [-n] [-o @var{offset}] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-t @var{cache}] [-w] @var{filename}
 ETEXI
 
 DEF("check", img_check,

qemu-img.c

@@ -3515,6 +3515,7 @@ static int img_bench(int argc, char **argv)
     bool is_write = false;
     int count = 75000;
     int depth = 64;
+    int64_t offset = 0;
     size_t bufsize = 4096;
     int pattern = 0;
     int64_t image_size;
@@ -3532,7 +3533,7 @@ static int img_bench(int argc, char **argv)
             {"pattern", required_argument, 0, OPTION_PATTERN},
             {0, 0, 0, 0}
         };
-        c = getopt_long(argc, argv, "hc:d:f:nqs:t:w", long_options, NULL);
+        c = getopt_long(argc, argv, "hc:d:f:no:qs:t:w", long_options, NULL);
         if (c == -1) {
             break;
         }
@@ -3570,6 +3571,19 @@ static int img_bench(int argc, char **argv)
         case 'n':
             flags |= BDRV_O_NATIVE_AIO;
             break;
+        case 'o':
+        {
+            char *end;
+            errno = 0;
+            offset = qemu_strtosz_suffix(optarg, &end,
+                                         QEMU_STRTOSZ_DEFSUFFIX_B);
+            if (offset < 0|| *end) {
+                error_report("Invalid offset specified");
+                return 1;
+            }
+            break;
+        }
+            break;
         case 'q':
             quiet = true;
             break;
@@ -3639,10 +3653,13 @@ static int img_bench(int argc, char **argv)
         .bufsize    = bufsize,
         .nrreq      = depth,
         .n          = count,
+        .offset     = offset,
         .write      = is_write,
     };
-    printf("Sending %d %s requests, %d bytes each, %d in parallel\n",
-           data.n, data.write ? "write" : "read", data.bufsize, data.nrreq);
+    printf("Sending %d %s requests, %d bytes each, %d in parallel "
+           "(starting at offset %" PRId64 ")\n",
+           data.n, data.write ? "write" : "read", data.bufsize, data.nrreq,
+           data.offset);
 
     data.buf = blk_blockalign(blk, data.nrreq * data.bufsize);
     memset(data.buf, pattern, data.nrreq * data.bufsize);

qemu-img.texi

@@ -131,13 +131,14 @@ Skip the creation of the target volume
 Command description:
 
 @table @option
-@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [-n] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-t @var{cache}] [-w] @var{filename}
+@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [-n] [-o @var{offset}] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-t @var{cache}] [-w] @var{filename}
 
 Run a simple sequential I/O benchmark on the specified image. If @code{-w} is
 specified, a write test is performed, otherwise a read test is performed.
 
 A total number of @var{count} I/O requests is performed, each @var{buffer_size}
-bytes in size, and with @var{depth} requests in parallel.
+bytes in size, and with @var{depth} requests in parallel. The first request
+starts at the position given by @var{offset}.
 
 If @code{-n} is specified, the native AIO backend is used if possible. On
 Linux, this option only works if @code{-t none} or @code{-t directsync} is